Monitor and results computer system

Abstract

System used for aiding the operation of processes occurring in a power generation plant is disclosed which includes a logging technique for transforming input data from various pickup points into a universal, named system variable format usable by all system functions. Specified changes in time or in any system variable can cause a given log to be triggered into a storing state, or an outputting state wherein the stored data is outputted by a printer in a page oriented log print-out format. Also included in the system is a sequence of events interrupt technique wherein the detection devices located within the protective circuits are corrected for their respective time delays between the sensing time of a measured condition and the actuation time of the associated switching contacts. The correction is achieved by storing the predetermined values of the time delays associated with each of the detection devices, and subtracting such stored time delay values from the system detected times of actuation of the respective switching contacts, thereby deriving a corrected sequence of events indicating the correct order of occurrence of the events at the detection devices and, consequently, the initial cause of the event. The system also includes an alarming technique wherein alarm limit values are assigned for a measured system variable at a given point in the system, and realarm values are calculated so that realarming occurs when the measured system variable departs from the last alarmed value by a significant amount of change, thereby employing system discretion in selecting only the most important alarm conditions to be outputted. A CRT device is used for displaying the alarm information and operates with a reduced line format for those alarms acknowledged by the operator. Entry, removal and presentation of alarm data on the CRT screen is designed to present the data in a simple and easily understandable manner while maximizing the amount of data presented.

Parent Case Text

This application is a division of U.S. Pat. Application Ser. No. 308,770, filed on Nov. 22, 1972, and now U.S. Pat. Ser. No. 3,855,456, issued on Dec. 17, 1974.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a monitor and results computer system, and more particularly to a system which provides operation, performance and historical data for continuously aiding the operation of a power plant.

2. Description of the Prior Art

The conventional manner of handling log information to an operator is to have a scanning device, that is program controlled to convey information into the memory unit of a CPU. The log is a group of data which you identify by designating the log number. The log has a list of points and a value. The logging device can type out the identification of the log, time, point Identification Number(s), and the value(s). The storage of the logging device is the piece of paper. If one is activating the log every 5 minutes, 5 minutes later the log program will be scheduled to gather the data for the log. From the operator's standpoint, the human standpoint, he sees what is going on by looking back at the lines on the piece of paper. To accomplish this may require one typewriter per log which is impractical.

In such state of the art printing devices used for printing log data, a large number n are placed in a format wherein generally a single log occupies a line on the printer. A log having a large number, such as 100 variables, would extend across the single line and the resultant printing paper was very wide. On the next line, a different log was printed. As a result of this type of format, a relatively complicated program is required with new headings being retyped for each new time a log is outputted. It is noted that other than the time dependent presentation of a printout, a demand dependent or a demand-on-program type of printout could be employed. For example, in a demand dependent set up, a user requests a log which is then assembled in a computer and then printed out on a typewriter. This typewriter was, according to the state of the art, conventionally a wide-carriage typewriter employing mechanical printing and the printed record on paper was the memory. The mechanical typewriters are used because of their adaptability to printing of a character at a time. On the other hand, printers using non-impact printing techniques are perhaps more ideally suited from the standpoint of the relative freedom from the high maintenance associated with the impact type printers and from the standpoint of speed. However, non-impact printers are not suitable to the applications in the conventional log data storage and printing systems because such systems have a printout format which involves the writing of a character at a time. This character at a time printout format is incompatible with the non-impact printers because the chemical preparation and development processes on such non-impact printers generally requires a relatively short interval of time between the chemical preparation and development steps of printing. Thus, when employing the state of the art non-impact printer in the conventional log data system, if the time interval between the printing of adjacent line is too long, then the chemical bath would overdevelop and wash out those lines which were not removed from development in time.

According to some prior art log printinig formats, a new heading comprising the various names identifications is retyped for each new line. Also, in logging systems used therewith, a demand panel is used to operate in conjunction with a program and special log programs containing lists for each special log. The program consisted of lists in the memory of the members (the names). These lists in the computer memory consisted essentially only of the names while a directory contained the addresses or locations of the names in the memory. A secondary memory device, such as a drum, contains the contents or value of data associated with the names in the memory.

Also, in many supervisory and control systems existent in power plants, overload and protective devices are employed. These devices are connected within a protective circuit and, upon their actuation, provide the system with an indication as to the source of a problem within the power plant, such as a loss of generator power or a boiler trip. Contact changes from the protective circuit network, including the overload devices and protective relays, were incorporated into computer systems and attempts to program the computer to indicate the relays or other protective devices which were activated and the times of activation of their switching contacts have met with common problems.

The protective circuits commonly include a multiplicity of trip devices, such as relays and switches. When a trip condition exists, one or more relays or trip devices are energized and their associated contacts are switched. For each given relay that is activated by a plant condition, there often is one or more auxiliary relays within the protective network that is also activated directly or indirectly as a result of the actuation of the first relay. For example, a first relay switch may have switching contacts which cascade into auxiliary switches which eventually cause a further relay to be activated. Therefore, even though a trip condition is initially sensed at a first relay, signals may be produced in the system which cause an auxiliary relay(s) or trip(s) to occur which may, in turn, indirectly switch other contacts in the system. Because of the hardware associated with the protective system, the contacts of the auxiliary relay(s) may switch over before the final contact that feeds the computer from the initial relay is energized. As a result, the computer or control system incorrectly sees the contacts of the auxiliary relay(s) being switched ahead of the contacts of the initial relay and interprets this as a trip caused by the function of the auxiliary relay. The computer also records the closing or switching of the other devices in the protective circuit and associated or effected plant devices, and records their respective times of occurrence of switching and the status of all the devices.

Thus, another problem existing in the prior art monitoring and control systems for power plants is that, because of the different delays associated with the individual relay and tripping devices between the precise time of the occurrence of the alarm condition or "event" and the actuation of the contacts of such devices, the monitoring and control system indicates the incorrect cause of the event since the system is made aware of such event only upon the actuation of the contacts.

Conventional alarming systems, such as those used in power plants, provide scanning devices which compare desired system characteristics, such as a boiler temperature, to stored low and/or high alarm set points previously designated or calculated for that point. The alarm information status is output on printers, typewriters and on trouble location annunciators providing audible and/or visible warnings of an alarm condition. One problem existing in conventional alarming systems is that a plant emergency may result in a multiplicity of alarms being set off almost simultaneously, such as those due to a failure of the main turbine which in turn interacts with other equipment so as to cause other alarms to be actuated. In some systems, in addition to both high and low alarm limits being set for a particular device, there is provided one or more realarm conditions which are set to occur when a point previously in alarm is detected as having changed a prescribed significant amount, either above or below the last alarmed value. Even here, often this prescribed significant change, hereinafter referred to as "delta", is normally small to detect and follow or track the deviations of the value once it is no longer normal. The large transients induced by the loss of the equipment result in the occurrence of several alarms almost continuously being set off for the given equipment and any related plant systems.

Alarm status information is presently being output on printers, typewriters, annunciators and CRT devices. It has been found that the outputting of alarm information by such devices is often confusing or unnoticed to the human understanding because of both the large amount of information being simultaneously displayed as well as the format by which such information is presented.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a monitor and results computer system which is both practical and efficient from the standpoint of computer storage cost, processing time and outputting.

It is another object to provide a logging system which permits the equivalent of wide page printout on narrow paper.

It is another object to provide a logging system which is able to easily change the log members.

It is another object to provide a logging system wherein the stored data is universally usable by all system functions.

It is another object to provide a logging system wherein the log page information in the memory is compacted together in an easily printable form, with minimum processing required.

It is another object to permit storage of such information in a second level memory, instead of on paper.

It is another object to provide a logging system which can easily process via the log name, the defined variables of that log.

It is another object to be able to output both past and present data without the need of continuously outputting.

It is another object to provide a logging system which can make any log available on demand, or upon the occurrence of a condition or event.

It is another object to provide a logging system which generates data on a page at a time output basis, thereby making effective use of non-impact low maintenance printers.

It is another object of the present invention to provide a monitoring and control system which produces the actual and correct sequence of events interrupts occurring in the plant overload and protective devices.

It is another object of the present invention to provide outputting of alarm information in a simple and easily understandable manner.

It is another object to provide current, pertinent alarm information to the human operator which is determined as being the most significant.

It is another object to provide an intelligent reduction in the amount of alarm information presented to the human in a given system.

It is another object to provide a CRT display of alarm information which is easy to understand and is formatted to provide only the necessary alarm information arranged in a logical fashion.

It is another object to provide a CRT display for alarm information which is formatted to maximize the amount of data presented.

It is a further object of the present invention to provide a system which compensates and corrects for failure of any of the input devices measuring the system variables.

These and other objects are achieved by the present invention which provides a logging system within the monitor and results computer system wherein analog to digital input data is presented to the computer system from monitoring devices, such as transducers and thermocouples located at various pickup points external to the computer system. The input data is scanned and transformed into a universal, named system variable format usable by all system functions. The format includes the name identification of the variable, the value of the system variable, the quality of the data and the time at which data is obtained. The name or member of each log is defined by the format. Triggering conditions are defined for the system such that specified changes in time or specified changes in any system variable can cause triggering of a given log into one of two active states. Generally, a Free log state represents the log number and is a log number list without names or page assignments. a Defined but yet inactive log state includes names only. An active log includes both names and values correlated with times or time intervals, and an Active outputting log state includes not only names and values, but also a demand for the printing or displaying of a log. If a log is changed or triggered to the active state or to the Active outputting state, then the log data is stored in the proper log page field at the proper index location. The log page format is designed for use with page oriented printers, wherein each page includes a log number, and a log heading containing the names or identification of each member of the log. These names are individually arranged in the heading at the top of the page in separate columns. In addition, each log page includes the time indication of the data on each line.

Generally, the program is designed to handle all details following the request by a human to place or change a point in a log, without any further human intervention. The program is designed to define log lists, report or remove members of the lists and to allocate pages. The program also is designed to be triggered by events or times, to set and control printout. Also, the program is designed to control log status. The use of the universal format with named system variables, the formatting and storage of data in log page field and the final format of the page oriented printout provides a system with the ability to easily change the types of logs, i.e., change the log members or add to the logs.

The present invention also provides a system and method of deriving the ordered sequence of interrupt events sensed by detection devices connected within a protective circuit wherein such detection devices are characterized by a time delay between the sensing of a predetermined condition and the actuation of their associated switching contacts, comprising means for detecting the change of state of the respective switching contacts associated with each of such detection devices, means for storing values of time delays associated with each of said detection devices, such time delays representing the known delay for a particular contact between its switching time and the actual time of occurrence of the event at the associated protective device, the time of actuation of such switching contacts being detected by the system, means for subtracting the stored time delay values from the detected times of actuation of the switching contacts of the respective devices to produce a corrected time of initiation of the event at the respective devices, whereby a corrected sequence of events is derived which indicates the correct order of occurrence of the events at the devices and, consequently, the initial cause of the event.

The storage and computations are carried out by the monitor and results computer system of the present invention which receives indications of the real time of switching of the device contacts and applies the associated corrective time delay for the particular contacts to produce the actual time of activation of the protective device. The system and method according to the present invention is thereby able to determine the actual interrupt event which initiated the protective devices.

The present invention also provides an alarming system and method which includes the assigning of an alarm limit value for a measured system variable at a given point in the system, scanning such point for the measured system variable even after such an alarm value is detected, calculating and applying a second alarm value representing a significant change (a delta) in the measured system variable from the last alarm value, and outputting the system variable information existing at each of such realarm values.

The method also includes the setting of a fixed significant change (a delta) associated with the measured system variable of a point whereby the second alarm and any subsequent realarms would ordinarily be set off when the measured system variable departs from the last alarmed value by this fixed amount. In addition, the method includes changing this delta for a given point by selecting a multiplier which is applied to the fixed delta to produce a different delta which then represents the current value of the significant change in the measured system variable. This current delta will require the next alarming of the measured system variable value. The use of the multiplier to calculate a significant change of the system variable value by which the second or any subsequent alarm is to be set off allows the application of discretion in selecting only those very important alarm conditions to be outputted, thereby minimizing the number of alarm outputs.

A CRT device is provided for outputting the alarm information and instantly displays eachh alarm, when first detected, on the next free line above the most recent new alarm, starting at the lowest line of the alarm area of the CRT screen and moving upwards. When an operator acknowledges the alarm information, the alarm message is automatically changed to a reduced format wherein the current value, current direction, current deviation from the alarm limit value and current duration of the alarm is updated at the scan frequency or the calculation frequency of the measured point. When the CRT screen is filled with alarm information, that is, the top line of the CRT alarm area is occupied, the oldest group of alarm messages at the bottom of the screen is transferred into a system memory for alarm backlog information and the alarm information on the lines above those transferred shall be compacted downwards, thereby permitting entry of the new alarm at the first free line above the existing displayed alarms of the alarm area.

When the value of a measured system variable at a point was previously detected and displayed in the new alarm condition, and such point is further detected as having changed by a significant amount by crossing the computed delta value above or below the last alarmed value, and such point is not on the "no alarm" or normal side of the alarm limit, then such point will be displayed on its present line of the CRT screen in the new alarm format until acknowledged by the operator, at which time the alarm information is returned to the reduced format. However, if the measured system variable alarm message had been previously moved into the backlog of alarms, the alarm message shall be removed from the backlog and placed on the next free line determined in the alarm area.

It is to be understood that, as used herein, the term "named system variable" includes a measured system variable, and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of the monitor and results computer system of the present invention;

FIG. 2 shows a printer output format for a log page, illustrative of the present invention;

FIG. 3 is a block diagram showing the four log states;

FIG. 4 is a generalized system operation flow diagram;

FIG. 5 is a more detailed operations flow diagram of the diagram shown in FIG. 4;

FIG. 6 is a representation of the operator/engineer panel;

FIG. 7 shows a flow chart of the operation for defining a log;

FIG. 8 shows a flow diagram of the operation for changing the status of a log;

FIG. 9 shows a flow diagram of the operation for controlling the collection and/or outputting of log data;

FIG. 10 shows a protective circuit connected to the computer control portion of the system which computes the actual sequence of events detected by overload and protective devices;

FIG. 11 shows a graphical representation of a curve plot of a measured system variable at a point, with the set alarm values, the set realarm values and alarmed values drawn to illustrate the alarming system;

FIG. 12 shows a CRT screen having an alarming area for displaying alarm information in accordance with the format of the present invention;

FIG. 13 shows a generalized functional block diagram of the alarming system;

FIGS. 14A, B, C, D, and E show the sequence of presentations of the log trend;

FIGS. 14F, G, H, I and J show the sequence of presentations in a prior art trend display;

FIG. 14A is a graphical representation of a tuned output signal (Believed Value) as the input signals are varied;

FIG. 15B is a block diagram of a tuning system for deriving an output (Believed) value used for system maintenance; and

FIG. 16 shows the method for deriving a Believed Value and accordingly applying system maintenance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a block diagram of a monitoring and results computer system used for aiding the operation of processes such as occurring in power generation plants. The system is generally shown by a block diagram. Block 10 refers to the sensing devices throughout the plant that provide the information to the computer system in analog, digital and/or pulse form. Block 11 represents the interface and filter circuits for filtering and conditioning the digital and pulse type signals and interfacing them with the computer system either through the CPU and/or the input/output processor. The block 12 represents the filter equipment and the scanning devices to handle the analog signals. Block 13 includes the control of the multiplexing for scanning. Block 14 is the representative of the logic and arithmetic circuits associated with the CPU. Block 15 is the programming and programming system that directs the logic arithmetic circuits 14 and memory accesses to perform the desired sequence of instructions yielding the monitoring services. Block 16 represents the actual CPU internal control. The computers used in this function are mainly interrupt type machines and represent a small to medium level CPU with respect to the present art. Multiple CPU' s are also utilized where required. The systems shown usually include multiple levels of memory and high memory transfer rates. Block 17 shows the high speed working memory. Block 18 represents a secondary level memory and block 19 represents tertiary level memories. Various levels of memory are utilized depending upon the speed of response required for the programming contained therein. Block 20 represents the input/output processor having the logic, control and associated memory mechanism for processing, formatting, etc., all system input and output data, and for regulating the connections among system information units and transfer control of information needed to be exchanged or transmitted between external peripheral devices and the internal memories. Block 21 represents the hard copy output devices such as printers and/or printer plotters of various types. Some of these devices 21 are used for permanent historical records, others for the printing information of temporary or "tear off" use in operations. Block 22 is a group or groups of alphanumeric presentation devices, such as CRT's for display of information of immediate or transient rise that doesn't require hard copy. Block 23 is a group or groups of combination alphanumeric and graphic display types of CRT's or graphic types, for use similar to devices 22 but with pictorial capability. Block 24 represents a combination type CRT that is used both for display and in conjunction with the operator/engineer keyboard console requirements which are shown by numeral 25. The block 26 represents interfacing circuits providing translation and adaption equipment required to pass information from the subject system to the other data systems.

Generally, the system shown in FIG. 1 permits the functioning as will be described in detail hereinbelow.

The logging system included in the system of the present invention is designed for use with page oriented printers. An example of the printer output format for a page is shown in FIG. 2. In page oriented printing, each of the system logs is identified by a unique number indicated at numeral 30 as "Log 66," and a log constitutes a group of data associated with such log. Each numbered log has associated therewith an English identification indicated at 31, which is assigned from changeable programmer input equipment and from an on-line change or compiling system. This English identification, i.e. "Turbine Inlet Conditions," is prined on each page in the log. Each log is made up of a series of pages, such as up to 10 pages, with each page containing a multiplicity of system variables, such as 16. In FIG. 1, the corners of the page define the log number 66 and page number 1 as 66/1. Each system variable in the page has a capacity of, for example, 40 lines of time-sequenced or other readings.

Included in the log heading are the year, month, day of the month, day of the week, hour, minute, seconds, and time interval between logs for the data on the log page. Also, as indicated by the bracketed area by numeral 32 is a list of the point numbers together with an english description of each of these points. In the example shown, there are 16 points respectively set forth in the 16 columns listed across the page. As shown by the heading area 32, column 1 is a listing of times, column 2 is a listing of the main steam at throttle, etc.

In addition to the log heading, each page includes heading and data identification information for each variable assigned to that page in accordance with the sample shown in FIG. 2. Thus, the page 1 of each log may include as one system variable the time of the data on that line. The logs can be assigned at repeat collection frequencies extending, for example, from one second to one day.

The system specifies an organized naming system for system variables that is constant throughout thereby simplifying the task of selecting and requesting information from the system. The system provides a method of grouping associated operating information, which is organized on the basis of functional lists, referred to herein as Log pages, so that simple requests will generate all associated information. As will become apparent from a reading of this specification, the Log page lists can be easily created by non-computer trained personnel and modified by the plant operators and engineers. The logging system is organized so that hard copy is generated on a "page at a time" log output, thereby making effective use of non-impact low maintenance printers. Also, the page oriented logging system permits continual acquisition of desired log data with the option to receive the latest page or pages of data upon demand or upon the occurrence of a predefined event.

This system also facilitates the generation of a graphic display of the trends of selectable data from active log pages. A Log Trend CRT can be used to trend information on the screen of one or more points in any active log or logs. A trend information display can be initiated by the demand panel to display trend information such as, identifying heading, Pen ID, Point ID, English identification, quality, present value, present engineering units, scales, and others. The request for Trend Pen Recording and for CRT log trend display can be generated and controlled from the operator's panels. All points assigned to the operator's recorders can be identified and the current value displayed in a specified format on the Trend Information CRT. It is noted that the CRT display of log output data can be used for outputting as an addition to or substitute for a log page printer.

The page oriented printed format according to the present invention comprises a given log content in a full page of information with several points of information located on one line for a given time. Thus, a request by a user for a given log will provide a page of printed information with the present log time and the previous 30 or 40 log lines of information for the same log. This is ccontrasted with some prior art logging formats which print out substantially a different log on each successive line intermingling unrelated sets of information with one another.

The logging format makes it more practical to have a larger quantity of information in storage in memory such as the names, the addresses or location in memory and the contents or value of the names in memory. Of course, the amount of information contained in memory will depend to a great extent on the trade-off between the amount of memory available as against the processing time limitations. Generally, with the page oriented printing technique according to the present invention, the memory comprises a pool of pages of information with each page of information similar in content to the data to be printed out on the printer for a given log. Of course, the data in memory can be assembled to a lesser degree than that described above in which case processing and assembling of the data into final form for a page will be required.

In the page oriented printing format a printer may typically accommodate 16 columns of information. Since many of the logs contain more than 16 items of information at a given time, then the pages of print are arranged in a fashion to accommodate a large number of columns of information for a given log, such as 160 columns of information. In this example, 10 pages of print will be arranged in a strip in series, with each page comprising 16 columns of print for the same log all on a time synchronized basis. Thus, page 1 may contain data values for a first 16 names or points of information at various times indicated, page 2 will contain data points 17 through 32 taken at the same time as the data on page 1, page 3 will contain information for points 33 through 48, etc. Further, the heading on a given page need not be changed for each line on such page since each of the page lines contains data associated with the points or names in the heading at the columns on the top of the page.

As an example, assuming that a single log contains 273 characters or 33 names with data for each point at a given time and that single page contains 16 columns, then 3 log pages will be required to present this data. While this ordinarily would require a very wide paper, the page oriented printer arranged the pages in a strip series arrangement.

The system includes a naming scheme such that related items have one unique basic or root name throughout the system. The root name and suffixes are also referred to as point identication or ID number. All references to a point by the operator and the source language programs use the basic name plus any desired suffixes. As an example, a basic name can have the form:

Pnnnn,

where:

P = a prefix from the list below

Nnnnn = a number from 0 to 9999

The prefix can be assigned according to the following:

A (or Blank) Analog Input

B boolean/bit

C constant

D digital Input

F fast Calculation

G spare (Reserved for GROUP NUMBERS)

H spare

I summation Boolean Changes

L spare

M memory Location

P performance Calculation

R relay Output

S special Analog (Composed point)

T maximum of N Points

W minimum of N Points

X variable from Common

The suffixes applied to the basic name for indicating processing or transformation on a point is instituted by appending the transform-related identifier to the basic root name. Suffixes can be multiple-level. At that time, the new point is created. The suffix can be consistently assigned according to alpha representations, such as A=Periodic Average, B=Periodic Minimum, C=Continuous Running Average, D=Daily Average, F=Daily Minimum, etc.

All analog and digital type variables are stored in the computer memory with a quality code associated with the value which is, for example, in range of O through 3. The quality code is generated along with the value and is always propagated through transforms and calculations. Data quality levels can vary between the numbers O and 3 where the O represents good data quality and the 3 represents bad data quality. All printed or displayed messages are adapted for including a quality identifier along with the value.

In order to make the system operable the following needs of the operator must be met: (1) requests that the log information be presented immediately; (2) requests that the log content may be changed; or (3) requests that the log information be presented at specified time intervals, i.e., every hour. Each log may be in one of the following four states.

Every log carries with it a built in trigger, i.e., IF statement which is selected by the operator by, for example, activating log 44 if D103 (pump contacts) go off and if an analog value goes above a certain defined state or value, or system activity previously determined or changes of quality.

Referring to FIG. 3, the four log states are shown in a block diagram form. Here, the Free (Undefined) Log State O represents the log number without labels in the log and without page assignment. Generally, the Free Log State O is a log number list without names. The Defined (Inactive) Log State 1 includes names. The Active (gathering but Non-printing) Log State 2 includes both names and values at specified time intervals of collection. The outputting (gathering and Active Printing) Log State 3 includes not only names and values but is outputting as well as collecting.

In the Free State, the log is available for definition and uses no pages. A request to print or report a Free Log shall report to the requesting station immediately the message that the log is "Free."

In the Defined State, the log has some system variables assigned to its columns but it is not gathering or printing. Logs are moved from the Free State to the Defined State by panel function and/or the on-line background compiler. As the log is Defined, the Operator designates the column and the ID of the system variable assigned to that column. Column number in excess of 16 causes the system to automatically utilize additional page(s), and the mechanism continues for multiples of 16 up to 10 pages. Logs with high collection/printing frequency require 2 memory pages per log page to provide time to print. The Operator can insert blank columns for formatting as he desires. A request to print or report a Defined Log shall cause the standard log headings, "variable" heading, and one line of the latest available value of the corresponding system variables. All of this is printed on a Page basis by the printer associated with the requesting panel, unless a different printer is requested or is automatically substituted by the system itself.

A Defined Log may be moved to the Active State by either panel function or change of state to a prescribed direction of a flag bit set by an event triggered program. In moving from Defined to Active State, a collection frequency is specified either by the panel function or the initiating program or the previously designed frequency if a new one is not supplied. In the event of a conflict, the program prevails. The Active State causes the logging system to collect the values associated with the system variables contained in its page list(s) at the respective frequency defined for the owning log. As this data is collected it is written to the system drum/disc (secondary) memory. Each log page contains, for example, enough storage to provide heading information and forty lines of data. Output has a total of 52 lines of l32 characters/line. Three additional lines of storage are provided to buffer for the print time. The logging program continues to overwrite the oldest line, thus keeping a full Page of log available for instant printing on demand. When the "fast" logs (i.e.: interval less than 30 seconds) are moved to the printing state, two Pages can be alternated-- one being printed while the other is being filed by the logging program.

The state change from Active to Outputting is initiated by panel function or by prescribed direction change of state of a second Flag bit. When output is requested by panel function, the present contents of the log is immediately printed, and each new Page of data (forty lines) is automatically printed until the panel function requesting outputting is cancelled. Where printing is initiated by event, the digital action program controlling the print determines both the number of readings to be taken before printing is initiated and the duration of the printing. In any case, where printing is initiated by event or event delayed, the time of the initiating event will be stored as a line of data in Column 1, and asterisks written into that corresponding line for all other columns of that line. All logs with event triggering are capable of manual triggering with or without delay to print.

Either the Active or the Output Report of an Active log will cause full headings and data of the current page to be printed on the printer associated with the requesting panel, unless otherwise requested.

As an example, Pages to be assigned for logging can be taken from a system pool of 280 pages. Assuming that the logs described previously are numbered 1-99, this pool includes the Pages for Series 100 logs as well as Special Logs.

Series 100 logs include;

A: Tabularized log 101 which is the formal log of up to 10 Pages;

B: Log 102 which includes the formal Daily Logs of up to 10 Pages;

C: Log 103 which is the Operational and TurbineTrip Analysis of two Pages, and one-second frequency;

D: Log 104 which is the operational Data and Turbine-Trip Analysis Log up to five Pages of Fifteen-second frequency;

E: Log 105, 106, 107 which are assigned to the Turbine Data Log for operation at predetermined value openings once a day, and turbine roll to half load, or trip to turning gear plus 10 minutes, and also from certain analog or contact variables associated with the turbine exceeding preset limits; and

F: Log 108 to 110 are spare.

Every log has the abiltiy to take on the above defined four states and to move forward and backwards within such four states as shown in the arrows interconnecting the blocks. With the above logging system, no programmer is needed on call since the program in operation is under the full control of the plant operator or user.

There are generally three types of system variables, these being of the analog type, the boolean type and the reference type. The analog type varibles consist of points having values represented by more than one bit plus quality. Analog type variables include analog inputs, constants which are generated by the program or entered via the operator's panel, fast calculations, performance calculations, common variables and others. Boolean type variables consist of points having values represented by one bit plus quality and include variables such as digital inputs, relay outputs and boolean bits (flags). Reference variables provide memory location identification and include memory locations in core or drum/disc for the purpose of references to the contents of those locations.

The logging system can be used to provide both tabular data and graphic or curve representations of the system variables. The curve representations are generally used where the logging system is in the active state and the data is moving rapidly or has just gone into alarm status. Here, the system is programmed to produce curve vectors to define the various operations. The system finds the desired information via the log lists and produces a log trend of the point at the present time and during the period of 40 logged readings preceeding the present time, such as for the last 40 seconds or 20 minutes, etc. The generation of a log trend for a point is, therefore, made by a system which can be characterized as an on line real time system.

The system includes a log trend CRT display which can show trends of up to four points, for example, in any active log or loop. When trend is initiated by operation of ANALOG TREND (Button 126b shown in FIG. 6) the system displays the equivalent, suitably scaled analog tract from the values stored in the appropriate log page (FIGS. 14A - 14E). FIGS. 14F-J represent a prior art display (identified as "WITHOUT") in which there is no trend presentation at the time of commanding a trend presentation since such a display included no structured stored data.

A time scale grid can be displayed according to log frequency. The trace can be suitably updated and "advanced" with each new log line stored into the log pages.

The log trend CRT display enables operating difficulty to be displayed immediately by back tracking a number of prior log readings, to log readings, by way of example. As a result, effects of immediate operating action are instantly displayed for tracking correction action.

Referring to FIG. 4, there is shown a system operation flow diagram. The system can be characterized by four general operations. The first operation comprises the transforming of analog and digital input data on lines 46 and 48, respectively, to the computer into a universal format usable by all system functions, indicated by the numeral 50 in the FIG. 4. The universal formats, indicated by the numeral 52, includes the name, the variable (quantity), the quality and the time. Thus, the log members are defined by the name, value, quality and the time. Therefore, the log members are defined by the universal format, and the input data is transformed into such format.

The second general operation comprises the defining of triggering conditions for the system, such as a specified change in time .DELTA. T or a specified change in a variable in the format. In the system, log triggering, indicated at 54, can be initiated by any condition at pickup points under measurement, such as a boiler, turbine or a generator, or by operator set tables of adjustment.

As indicated above, every log has associated with it a built in trigger (or IF statement) which is activated upon the occurrence of the preset trigger conditions. Upon the occurrence of a trigger for a given log, the third general operation of the system involves a means of controlling the changes of log status with respect to four log states defined above, as indicated by numeral 56. That is, when a trigger ocurs, control means are provided which effects a change of status from the Active Non-printing state to the Active Printing State, from the Defined state to the Active state, etc., as per the arrows shown in FIG. 3. If the log status is designated, then the system triggers a change of status of the log to such designated state. It is noted that there can be different types of triggering; the trigger need not be instantaneous, but can be delayed.

The fourth operation of the system involves the formatting and storage of data in the proper log page field as indicated by numeral 58. If the data is a number of a log and it is the proper time to store the data on an active log list, then such data is formatted and stored in the proper log page field at the proper index spot, thereby providing a set up for an efficient output on all proper log pages.

The fifth operation comprises the data retrieval from the log pages, final format and print out, indicated at numeral 60, of the log page in accordance with the page oriented printing format described above.

Referring to FIG. 5, there is shown a more detailed operations flow diagram of the diagram shown in FIG. 4. In the FIG. 5, identical numerals are used to denote identical portions of the system shown in FIG. 4. Specifically, analog and digital input data is received in the computer on lines 46 and 48, respectively, and presented as scanned input data at 62. The signals are received from transducers, thermocouples, etc. located at various parts of the measuring system. The scanned input data at 62 can be transformed by special and programmed calculations into calculated data at 64. Both the scanned input data at 62 and the calculated data at 64 are applied as quality and variable into the named system variable format at 52. Also, data relating to time is provided from a time data block 66 to the named system variable format 52. In addition, memory cells 68 containing names are provided for the named system variable format 52.

If there is a change of state of the named system variable 52 it must be determined at 74 whether this change of state should cause the log to trigger. On the other hand, if there is no change of state at 70 as indicated at 72, then the pickup point must be examined for other items. It is noted that the named system variable package which includes the name, the variable, the quality and the time is stored in the current data field.

Each analog type and Boolean type variable can be assigned separate limits or a limit index to trigger an associated program. For Boolean type variables it shall be possible to specify the direction of state change to trigger the associated program. These programs will be used to manipulate scan frequencies, log events or events delayed, and other special system actions. Once a program is triggered, retriggering shall not occur until the triggered program has been serviced.

If the change of state at 70 is programmed to cause the log to trigger at 74, then the program will control the log status as generally indicated by numeral 56. More specifically, the program is designed to control the log status by either changing the log from the active, non-printing state to the active printing state at 76, or from the defined inactive state to the active state at 78. If the program is such that there should be a change from the active non-printing state to the active printing state at 76, then the log is changed at 80 to print status for a period .DELTA. T. If the program is such that there should be a change from the defined inactive state to the active state at 78, then the clock is changed to the active state at 82 for the time interval .DELTA. T.

If the log is changed to the print status at 80 or to the active status at 82, the log package is then stored at 58.

There are two alternate approaches which can be employed for storing data. The first approach requires that if the data is on any active log list at 84 and it is time to store the data in a defined list at 86, then the data is formatted and stored at 88 in the proper log page field at the proper index spot. In the second approach, if the data is on any active lists Y at 90 and it is time to store the data in this log list Y at 92, then the data is gathered at 94 from a storage buffer or tape. The first approach, 84, 86, 88 represents a separate job technique, whereas the second approach, 90, 92, 94 represents a tagged technique.

The use of the universal format with named system variables, the formatting and storage of data in log page field and the final format of the page oriented printout provide a system with the ability to change the types of logs, i.e., change the log members or add to the logs.

The logging system is designed to known: the facilities to define log lists, to report or to remove members of the lists, and to allocate pages. The logging system also is designed to be triggered by events or times, to set and control printout. Also, the logging system is designed to have the ability to control log status.

Generally, two types of logs are known;

1. Formal logs which are produced periodically and are not changeable by the operators but may be changed by special function of the plant engineer; and

2. Special logs wherein members are placed into or removed from the logs by the operators and the logs are of a periodic nature, or the logs are triggered.

In defining a log, there can be assigned any system variable point to any special log. Any value having a system name shall be permitted on a special log. Also, any point (names system variable) can be assigned to any column of the special log. As shown in FIG. 6, the Assign Log Button 119 of operator/engineer panel 118 is pushed. The log N number, column and system variable name are entered by means of buttons 120. Then the EXECUTE command button 121 is operated to cause the specified named system variable to be assigned to a log column. In the example, column 17 automatically starts the second page, column 33, the third, etc. A similar sequence, with the CANCEL command button 122 causes the removal of a system variable name from the specified column. This causes blanks to appear if the column is printed or displayed. A special case of CANCEL command is provided to permit assigning blanks to all the columns of a particular log, thus in effect making the log "Free." Log assign (button 119), log number (buttons 120) and REPORT operation (button 123) causes the entire heading and system variable names to be printed or displayed with the latest value of each column.

Any log can be activated by demand. The Operator may insert or change the period collection (from 1 second to 1 day), or alternately specify it to be set up for activation by change of a specific bit. This is accomplished by pressing button 119, tabulating with the tab buttons 120 to set the frequency field, entry of the frequency number of buttons 120, and pressing of EXECUTE button 121.

Any number of logs can be activated at any time and at frequencies compatible with system variable creation states. It is noted that named system variables may appear in more than one log at the same or different log collection rates.

Referring again to FIG. 6, operation of COLLECT LOG (button 124), LOG NUMBER (buttons 120) and a CANCEL command (button 122) will stop collection of log data and return that log to the Defined, not Active state. If printing, it also stops printing on completion of the present page.

When activated, a similar sequence of operations plus operation of a REPORT command (button 123) will cause the full log headings, system variable descriptions, etc., and contents in any log storage, including latest system value of all assigned named system variables and pages to be printed. If the display button, 125a of button array 125, is down, the first page shall be written onto the selected screen frame in normal group output format. Subsequent pages can be seen upon operation of "Page For More" button 126a.

Referring again to FIG. 6, the operator can request the output of any log, by number from the panels. Special buttons (FIG. 6) are supplied for the FORMAL LOG (button 127) and SHIFT REVIEW (buttons 128). When immediate output is required, an EXECUTE command (button 121) is selected. The selected log will immediately be printed on the printing devices associated with panel 118 unless otherwise requested at EXECUTE time.

At EXECUTE time, any log can be alternately specified for event or event delayed printing and an appropriate bit change specified to trigger this. An event or event delayed activation time-of-event occurrence, shall be stored in column one of the next line of the next log page and all other columns blanked. The output should then proceed for event types, or proceed after collection of additional lines in the event delayed type.

When outputting an OUTPUT LOG (button 129) and a LOG NUMBER (buttons 120), a CANCEL command (button 122) stops outputting and returns the log to Active collecting state.

When outputting, OUTPUT LOG (button 129), and LOG NUMBER (button 120) are activated and if the DISPLAY selector (button 125a) is selected, the report is outputted to the selected frame in group format, one page at a time (via PAGE FOR MORE button 126a of array 126 of buttons).

According to the present invention, the log is both flexible and of the triggering type. That is, one can create a trigger from any variable you are working with, such as a boiler or generator pickup point(s). Because of the provision of the named system variables in the universal format described above, the system is able to set any conditions for triggering. This universal format comprises a name, a variable (quantity), a quality and time. The universal format containing the named system variable is usable by all system functions and enables the computer user to access the overall information of all the specified pickup points upon demand or in accordance with the programmed times or changes in state of the named system variables.

Depending on the particular computer machine employed, the formatting process can be divided in various manners, that is, if there is a shortage or limited amount of computer storage space then a format is employed which requires less information in the central storage, or less channel transfer capacity, but on the other hand, requires additional processing time. However, if there is plenty of storage space and transfer capacity and processing time limitations are strict, then a format will be chosen wherein the data is stored in the central storage in a form more closely resembling the format of the print out page, thereby requiring relatively little processing time.

Referring to FIG. 7, there is shown a flow chart of the operation for defining a log. A log definition is initiated by a request to enter, change or delete a named system variable of a log. The beginning of the flow chart for operation is indicated by the symbol at 130. The system retains at 132 the details for selecting the log number, the system variable name or blank, and the selected column assignment, if such a column assignment is requested. If there is as yet no selected column assignment, then the system will go to the next available column on that or the following page. Ordinarily, the human operator defines the log and selects the details thereof. However, the operation can be designed to receive the details of the log at 132. After the details of the log are held at 132, the status description for that log must be located at 134 to determine what the current state of that log is at 136. If the particular log N is currently defined, is active and storing or is active and printing, then the page I of such log N must be located for the selected or determined column J at 138. The purpose of learning at 136 whether the particular log is currently defined is that the condition must be known that the log exists before a particular log is altered. If the log N is not currently defined at 136, and it is a request for a blank column at 140, then it is not necessary to make a log assignment at 141 because nothing is being entered into a log or changed in a log. However, if the entry is not blank at 140, the status of log N is set to the defined state at 142 to select a free page from the pool.

On the other hand, if the log N is currently defined at 136, the page of the log N is located at 138 for the selected or determined column J. With the log page number and column located at 138, then a check is made at 144 as to whether or not the initial request was to enter or change a point (i.e., not a blank) or whether the request was for a blank log. If the request was for a blank log, then it must be known at 146 whether there exists any other named system variable on the log page. If there are other points on the page, then blank spaces are entered in the column for those points at 148 and a collector of values is notified at 150 that the old point is no longer needed in this particular log N. If, however, there are no other points on the page at 146, the system can remove that page from the log and return it to a Free Page Pool at 152, and thereafter notify the collector of values at 150 that the particular point is no longer needed in the log N. After the page is removed from the log and returned to the Free Page Pool at 152, if such page was the last page in the log at 154, then the status of such log page is set to the undefined state at 156 and that portion of the operation for the log page is terminated at 158.

Returning now to the determination at 144 that the request was to enter or change a log point (not a blank), this indicates that there is a value that is going to be entered or changed in the log. Due to this, a check is made at 160 as to whether the particular page I that has been calculated for this log has already been assigned. If the page I has not already been assigned, then a page is selected at 162 from the Free Page Pool and the selected page I is entered at 164 into the log N definition list.

If the page I is already assigned at 160 then a check is made at 166 as to whether there is a named system variable already in the column J of such page I. If there is a named system variable already in a particular position or column J, the collector of values is notified at 168 that the old log point is no longer needed in the log N. After the collector of values is notified at 168 or a free page is selected at 162 and the selected page I is entered into the log N definition list at 162, then the computer will enter at 170 the new named system variable into the log page I of log N at the point or column J of the format. Thereafter, the computer will notify the collector of values at 172 of the new named system variable for collection so that the collector is on notice that this new point is needed for the particular log N. This operation is terminated at 158.

Referring to FIG. 8, there is shown a flow diagram of the operation for changing the status of a log. A log status change is initiated by an external or internal request to change the status of a log at 190. This input request is saved at 192 and the current log status is located at 194. A check is made at 196 to determine whether the current status of the log is defined, active or active printing. If the log status is not one of these three conditions, (i.e., undefined) then the system characterizes this as an error condition at 198, because the log must be in the defined state before its status can be changed to any of the other states. If there is an error condition at 198, and the request is from a human at 200, the system informs a requestor at 202 that the log is not defined so that the human is aware that he will have to define the log if he is to change its status. If the input request is not in the form of a human at 200, then the system sends a message at 204 to an error handler stating that the log is inactive, is not defined, and that the error handler must identify the user making the illegitimate request.

If there is a positive condition at 196, then the system goes from one state to another to examine the log for the current status, and to set the status of the log to the desired condition. The three desired log status conditions which can be requested at 206 are: to make the log active in storing at 208; to make the log active in printing at 210; and to make the log inactive and defined at 212. To make the log active and storing at 208, a check is made to see whether the log is currently printing at 214 and, if so, the printing indicator is reset at 216 together with a request for termination of any printing that is in progress. In other words, the log has been printing at 216 and it is desired to terminate the printing and set the log status to the active storing condition at 218.

If the log is not currently printing at 214, a check is made to see whether the log is currently defined at 220 and, if so, the storing frequency is set up at 222 as per the input request and the log state is set to active and storing at 218. However, if the log status is not currently defined at 220, the implication is that the log is already actively storing, which is the very condition that is being requested. This infers that the input request was made in order to change the storing frequency, this being done at 224 per the input request. In this case, since the desired log status at 208 is to make the log active and storing, and it is determined at 214 and 220 that the log is currently active and storing, then there is no discontinuity in the storage status, but rather there is a shift in the frequency or time period at 224.

If the desired log status at 210 is the active and printing state, it is first determined at 226 whether the log is currently storing and, if it is currently storing, a check is made at 228 to see if the log is currently printing. If the log is currently printing at 228, the print/store frequency is changed at 230 as per the request of the input information and the log status is set at 232 to active and printing. On the other hand, if the log is not currently printing at 228, the printing frequency is set up at 234 and a request for printing to occur at the desired time is made via the printing control mechanism.

If the log is not currently storing at 226, then the control flag is set at 238 for the collector to begin storing values at the designated frequency. Also, the flag is set at 234 for printing to occur at the designated frequency, and the log status is set to active and printing at 232.

If it is desired that the log be placed in the active/ defined state at 212, this simply means that the log is to be returned to the defined state wherein both printing and storing cease. To accomplish this, the active printing request flag is reset at 240 and the active storing request flag is reset at 242 so that the status of the log is set to the defined condition at 244.

Termination of the operation flow chart for changing the log status is indicated by the symbol at 246.

Referring to FIG. 9, there is shown the operation flow diagram for controlling the collection and/or outputting of log data. This control action of log data is initiated at 252 by either a value, an event or time. The status word of a particular log L is then located at 254 and a check is made at 256 whether the status of the log is either active and storing or active and printing. It is noted that the term "printing" as used herein, is intended to include other outputting operations, such as a visual display on a CRT device. If the log L status is active and storing or active and printing at 256, and it is determined at 258 that it is time to store data for log L, then a list of all named system variables required for log L is collected at 260, all of the log L values are stored at 262 into appropriate locations for this time frame, and this stored set of log L values is added at 264 to the buffer provided for log L.

If it is not time to store data for log L at 258, or the stored set of values are added to the buffer provided for log L at 264, then it is determined at 266 whether log L is active and printing. If the log is active and printing at 266, and it is time to print the log L at 268, then the heading and format of log L is collected at 270 for outputting on the desired device and the prepared log L is outputted on the requested or designated device on request at 272.

Action on the collection and/or outputting of log data is terminated at 274.

SEQUENCE OF EVENTS INTERRUPTS

Referring to FIG. 10, there is shown a protective circuit connected to a system in accordance with the present invention. Protective circuit 280 includes several overload and protective devices illustrated by the FIG. 10. Specifically, there is shown a trip initiating device 282, a trip actuation device 284, an intermediate device 286 and a protective relay 288 for other independent trip initiation. Intermediate device 286 represents a chain of intermediate devices and the cumulative delay resulting therefrom. The device 288 is another protective device installed for a different purpose, but which, due to the natural coupling of equipment not part of protective circuit 280, can in fact be actuated by the physical item that caused device 282 to actuate. Since device 288 has a low cumulative delay time, this undesired cross-coupling can cause the contact from device 288 to actuate the final trip actuation device 284 before the recorded signal coming through chain device 286 arrives at device 284. This causes an erroneous allocation of the initiation of the trip.

Other switching elements may be connected in the protective circuit 280. The specific arrangement of the protective devices is not pertinent to the invention. Rather, the protective circuit 280 is shown for the purpose of illustrating that various protective devices connected in a power plant system are ordinarily interconnected in various cascade and series circuits with varying attendant delays. Therefore, the activation of any one of the protective devices will frequently affect the other devices causing them to be activated and their associated contacts will be switched For instance, the energization of the relay 286 might cause the protective relay to be energized.

The problem that exists with such a protective circuit 280 is that the control system 300 will detect only the actual occurrence of a switching operation of the contacts, which will ordinarily occur many milliseconds after the occurrence of the event affecting the device 282. Also, due to the external interaction of the devices in the protective circuit, certain ones of the contacts can be actuated before the actuation of the contact relay string reporting the particular protective device which sensed the event. For example, referring to the Table A below, there is shown in the left hand column a sample listing of the inherent time delays in each of the devices 282, 284, 286, 288 and 290 (expressed in milliseconds).

TABLE A.

TIME DELAY BETWEEN ACTIVATION TIME AND CONTACT SWITCHING TIME

Time Delay (282) = 40 milliseconds

Time Delay (284) = 25 milliseconds

Time Delay (286) = 80 milliseconds

Time Delay (288) = 35 milliseconds

Time Delay (290) = 70 milliseconds

Thus, if the chain represented by device 286 is characterized by an 80 millisecond delay between initiation of the interrupt event initially sensed by device 282 and the actual switching of its contacts 282a, and a device 284 has a 25 millisecond delay, then the occurrence of an interrupt at the device 286 may at the same time by way of contacts 286a cause an auxiliary trip at the device 284. Because of the various external interaction or chain of connections, the contacts 288a and 288b for device 288 may be switched ahead of the contacts of the device 282 which was the actual cause of the event, such as a boiler explosion. The control system 300 will detect the switching of the contacts 284a and 288b for devices 284 and 288, respectively, before it detects and records the switching of the contact device 282. This error is commonly found in protective circuits having a plurality of hardware devices.

To determine the actual or real cause of the event, the control system 300 includes a storage section 302 for storing the time delay characteristics of each protective device used in the protective circuit 280 for each path. Also included is a logic arithmetic section 304 for applying the corrective delay times held in the storage section 302 and timing circuit 308 of the control system 300. The input section 306 is connected to the protective circuit 280 for receiving signals from each of the switching contacts. The logic arithmetic section 304 receives signals from the input section 306 indicating the identification of the switching contacts which were actuated and the times of occurrence of the actuation. Logic arithmetic section 304 subtracts the time delays for the proper path stored in storage section 302 and associated with the protective devices, from the contact actuation times indicated on line 310 from the input section 306 and provides at its output 312 a corrected reading indicating an identification of the device and the actual corrected initiation time and corrected sequence of events. A plurality of devices may be listed in order of their occurrence of computed initiation times as compared with the time of switching of their contacts. For this purpose, the logic arithmetic section 304 or a separate logic circuit 314 may be employed.

The Table B illustrates the manner of operation of the logic arithmetic section 304 wherein the detected times of switching of the contacts of the various devices are received on line 210, the time delays associated with the respective devices are received from the storage section 302 on line 311, and the corrected actual time of activation of each device (event interrupt) is computer and provided at the output line 312 of section 304.

TABLE B __________________________________________________________________________ DETECTED CONTACT DEVICE TIME CORRECTED ACTIV- SWITCHING TIME - DELAY = ATION TIME __________________________________________________________________________ T.sub.Detect (282) - 40 msec. = T.sub.Correct (282) T.sub.Detect (284) - 25 msec. = T.sub.Correct (284) T.sub.Detect (286) - 80 msec. = T.sub.Correct (286) T.sub.Detect (288) - 35 msec. = T.sub.Correct (288) T.sub.Detect (290) - 70 msec. = T.sub.Correct (290) __________________________________________________________________________

After the logic arithmetic section 304 computes the corrected time of activation of each of the devices, it re-orders the data received by the computer control 300 according to the corrected sequence so that the actual interrupt event is determined. That is, the computer control 300 determines the correct sequence of activation of the devices by the alarm or interrupt event.

ALARMING AND DISPLAY DEVICES

Referring to FIG. 11, there is shown a graphical representation of a curve of a measured system variable at a point, for example the temperature of a boiler. The ordinate 330 represents temperature values (degrees Fahrenheit) while the abscissa 332 represents time. The curve of the values of temperature with respect to time is indicated by the numeral 334. The example shows the high limit alarm value set at 930.degree.F for the boiler and indicated by the numeral 336. It is noted that a low limit alarm value is also set at 820.degree.F, as indicated by the numeral 338. The temperature range between the high limit alarm value 336 and the low limit alarm value 338 is referred to as the "no alarm" or normal side of the alarm limits 336 and 338. A fixed value for the significant change, also referred to as delta, is set at 5.degree.F. This significant change, or delta, when added to the most recent alarmed value of the measured system variable, defines a band having an upper bound which is 5.degree. above the most recent alarmed value and a lower bound which is 5.degree. below the most recent alarmed value. When the value of the measured system variable reaches or exceeds this band, the measured point is realarmed and the band reestablished about the current value of the measured system variable. This current value is now the most recent alarmed value. If the measured system variable value is within the normal range between alarm limits 336 and 338, the delta does not apply.

In addition, each point in the system has a multiplier factor which is used to expand the delta value at times when the operation of the system requires a decision as to which of the alarms are the most important as to warrant being outputted on a CRT or other output device. Therefor, the multiplier factor is applied to the fixed delta value for those alarms which have been determined to be of less significance with regard to the current power plant status. The multipliers are uniquely selectable and applicable at each individual measuring point as a part of an algorithm and can be applied by program or by a human operator. The algorithm is comprised of the actual significant change or delta which is equal to the specified or fixed delta times the multiplication factor M. Thus, the use of the multiplication factor is essentially the application of a correction factor to an already existing computer used value in order that the alarm system be apprised of only the significant changes in the measured values after the initiation of the first alarm.

In the example, it is assumed that a multiplication factor M of two (2) is applied to a delta of 5.degree., thereby changing the effective delta to 10.degree.. If, due to the scanning frequency of the measuring device, the temperature of the boiler tube is first measured as crossing the alarm limit value of 930.degree. at a value of 932.degree., as indicated by the cross at numeral 340, then 932.degree. represents the most recent alarmed value. Since the new effective delta is 10.degree. (5.degree. times 2), then the next alarm value or condition at which the alarm message will occur is greater than or equal to 942.degree., as indicated by the numeral 342. If the measured value is subsequently scanned at 943.degree., as indicated by the cross at numeral 344, this represents the new alarmed value. This process continues in the same manner so that the next alarmed value will be greater than or equal to 943.degree. plus 10, or 953.degree., as indicated by the line 346, or less than or equal to 943.degree. minus 10, or 933.degree., as indicated by the line 347.

Referring to FIG. 12, there is shown a screen 350 of a CRT device employed for outputting the alarm information obtained by the system disclosed with reference to FIG. 11. Each alarm, when first detected, is instantly displayed on the next free line, L1-Lx, starting at the bottom of the alarm area 351 of the screen 350. Each of the lines L1-LX may contain alarm information for a single measured system variable in the system, as is indicated with the alarm information presented. The first alarm for a given measured system variable in the system is first displayed on a line in a "new alarm" format which utilizes the full width of the screen 350. As an example, the line L2 is shown as displaying a new alarm format wherein alarm information is displayed across the entire line L2 along sections 352, 354 and 356. When an operator acknowledges the alarm information displayed on the line L2, the alarm message is automatically changed to a reduced format wherein only the current value, the current deviation from the alarm limit, the current direction and the current duration of the alarm is updated at the scan or calculation frequency of the measured system variable. This reduced format comprises the portion of line L2 indicated by numeral 354. The heading for the data displayed in the alarm area 351 is indicated by numeral 358. As shown in the alarm heading 358, the new alarm format includes the point identification, an English description of the system variable, i.e., Boiler Tube 68 Temperature, the S representing the identification of the alarm limit which is being violated high or low, the D representing the direction in which the current measured value moved with respect to the last measured value, the current measured value, the engineering units of the measured value, the difference between the alarm limit value and the current value, the quality Q, the .DELTA. T representing the length of time the measured value has exceeded the alarm limit value (336 or 338), the low limit value, the S representing an indication that the low limit detector is on or off, the high limit value, and the S representing an indication that the high limit detector is on or off.

When the alarm area 350 is filled with alarm information, that is, the top line LX is occupied, then a group of the oldest alarm messages at the bottom of the alarm area is transferred into a system memory for alarm backlog information and the alarm information on the lines above those transferred shall be compacted downwards. This readjustment permits entry of the new alarm at the bottommost but unused line of the alarm area.

Referring again to both FIG. 11 and FIG. 12, it is noted that the occurrence of a new alarm at point 340 of FIG. 11 can be displayed in a new alarm format including sections 352, 354 and 356 of FIG. 12. After being acknowledged by the operator the alarm information at point 340 is reduced to the acknowledged alarm format covering the section 354 of the section 350. However, if the same measured system variable, shown graphically in FIG. 11, undergoes a significant change in the measured value to exceed the delta of 10.degree. set for such point, such as being measured at 943.degree. as shown by the numeral 344, then the line of the alarm area 350, which is displaying the alarm information for this measured system variable will expand to the new alarm format until it is acknowledged, whereafter this second alarm information is reduced to the narrow format.

Thus, it is seen how the alarm area 350 is used to convey two different states or conditions of alarm, these being the new alarm or wide format, and the acknowledged alarm or narrow format. Also, the alarm information remains in the same line position in the alarm area 351 as the original alarm information for the same system variable up until the time that the area must be rearranged for accommodating a new alarm message for which there is no free line at the top of the alarm area. This permits the operator to recognize a position or line on the screen as representative of a specific alarm message until the point in time at which the alarm area must be reorganized.

If a particular measured system variable, previously in the alarm condition, returns to the normal condition, the system and operator are notified on the return to normal and the alarm information is removed from the alarm area 351. At this point, however, the other lines are not shifted downward to fill in the removed line of information until the alarm area 351 is filled to the top line. The purpose of this technique is to maintain the alarm data in the same line position for as long as possible, as opposed to continuously shifting the data on the screen. Of course, as mentioned above, when the alarm area 351 is filled to the top line and the content of the alarm area is to be maximized, then a group of the oldest alarm information is removed from the alarm area 351 and placed in a backlog in the system memory.

FIG. 13 shows a generalized functional block diagram of the alarming system. The alarm data is received on lines 370 by a control unit 372 which controls the entry and removal of alarm information on the CRT screen 350. Control unit 372 also controls formatting and the position of the alarm information on each of the lines on the alarm area 351 in accordance with the described method, as well as controlling the removal of alarm information from the alarm area 351 into a backlog condition in a system memory 374. The alarm backlog in system memory 374 is made available for display on a visual information presentation device 376. Alarm data in the system memory 374 is made available for presentation by the device 376 upon request via an operator keyboard console 378 connected to the control unit 372. The measured system variables held in the alarm backlog of system memory 374 are updated in a similar manner as updating of the points on the CRT screen 350. When a measured system variable in the alarm backlog changes significantly past its designated delta, it is removed from the alarm backlog and reinserted once again on the alarm area 351 in the new alarm format at the next available line for an alarm message.

When a point which has been in alarm is determined to have returned to the normal condition, such point is removed from the CRT screen 350 or the alarm backlog of system memory 374 and indicated as returning to the normal condition on another area of the CRT screen 350 other than the alarm area 351.

The visual information presentation device 376 includes on its screen a display area 377 which functions as a keyboard input guide and verification. Display area 377 includes the four bottom lines of the screen of device 376 for presenting a memory of what the human was working on, even though the demand functions of the operator have been changed. The device 376 presents information relating to what was last carried out with the particular blank of information when it was used by the human. The device 376 enables the human to go back and see what he had been doing with a particular function, and then modify his last operation or condition. The memory information produced in the display area 377 is stored in a local memory 379. Thus, the display area 377 acts as a guide of the human inputs previously entered in the system and enables the human to simply fill in the fields to update the information rather than reentering a new set of information relating to the same item.

When a point has been in alarm is determined to have become a bad or faulty point, it is removed from the CRT or alarm backlog and is indicated as being a bad input. On the other hand, if a point has not been in alarm and is determined to be faulty, this is marked as a bad input and all user programs using that particular input are notified, and it is put into the bad input summary and name and status of this point is temporarily indicated on an area of the screen reserved for bad inputs. The system includes a bookkeeping arrangement which accounts for each of the points that activated an alarm and subsequently went bad. This is useful since the alarms must only be activated and maintained by good or suspect system variables.

BELIEVED VALUE

In the conventional plant condition measurement systems of the type wherein several inputs are connected, if one of the inputs is in error, then the output of the system is significantly affected by the error of the input device. In addition, sudden jumps occur in the output of the system, as the input device changes state from unacceptable to acceptable, and vice versa. With this incorrect output, the system erroneously signals for a corrective action leading to incorrect operating actions by either human operators or an automatic control system.

The present invention provides a system which compensates and corrects for the failure of an input or input device measuring certain conditions and involves a method of timing a circuit for the characteristics of the input measurements, thus permitting one input device to fail, be repaired and restored to use without significantly affecting the resulting output value of the system.

The present invention provides a "Believed Value" which is a mathematically determined number representative of the most likely value of an important plant measurement. A Believed Value is a special form of an analog composed point, and is a calculated value which may require manipulation of one or more analog inputs and/or other variables. For a critical plant measurement, multiple input devices, (direct or inferential) are installed to provide independent measurements. Generally, the Believed Value involves a technique wherein the relationships among the various inputs are compared for validity by combinations of the differences between any two of their indications. This method permits analyzing the disagreement of the input values and confirming the "agreed on" value as a "true" value for the critical item being measured. The system is designed to mathematically compensate for, and tag as Bad, the particular input device which is in error by a large amount. A lesser degree of error will be tagged as Suspect.

Each of the three input devices has reasonably compatible dynamics, such as time lags or responses to measurements in the same order of magnitude and each of the devices is designed to sense related conditions, such as pressure or flow. As an example, the described arrangement includes three devices for sensing pressure or three devices for sensing flow or three devices for sensing a liquid level. Since the three inputs are related to each other, when the readings in one input device vary, then similarly, the readings in the other input devices should vary if they are working properly. Where the devices are not measuring directly the same condition, they will be suitably scaled and linearized to give compatible numbers.

Tuning of the Believed Value is carried out by varying the output of one of the input devices while holding the other two at appropriate levels. The output of the input device that is varied is taken over the range of values likely to be produced by the input device and includes values that would represent the failure mode. At the same time, the output of the system is recorded over such ranges as these values are run, so that the performance of the Believed Value system can be evaluated. The tuning of this system is accomplished by adjusting the non-linear factor (NLF) which designates a band of reasonable variation and the non-linear power (NLP) which controls the degree of weighting provided for each value as a function of its deviation.

More specifically, tuning of the filter circuit to a particular set of input devices or transmitters for a particular process measurement involves the varying of the values of a non-linear factor (NLF) and a non-linear power (NLP). The non-linear factor (NLF) is a number derived from the probable disagreement between the readings of the input signals or devices, since there is involved a statistical uncertainty of known readings. The non-linear power (NLP) is a function of the type of Believed Value that one is seeking. For example, as shown in FIG. 15A, the curve 382 shows a particular Believed Value curve for a non-linear power (NLP) equal to four. Here, the inputs one (1) and two (2) are held constant at the values V1 and V2, respectively, while the value of the third input (3), shown as V3, is varied in accordance with the curve indicated by numeral 384. On the other hand, the Believed Value curve indicated by numeral 386 represents an NLP equal to one and has a smoother slope than the relatively steep slope characterizing the Believed Value curve 382. In this fashion, the tuning method is used to derive the values of the non-linear power (NLP) and the non-linear factor (NLF) which provide the desirable characteristics or shape of the Believed Value. Also, as will be explained in more detail hereinbelow, the tuning method produces those NLP and NLF values which are used to compute the Believed Values for the real values of the input signals.

Referring to FIG. 15B, the three inputs V1, V2 and V3 are shown as being applied on lines 388A, 388B, and 388C leading into a tuning circuit 390. Tuning circuit 390 includes means for adjusting the values of the NLF and NLP factors which are received on lines 392 and 394 from a tuning coefficient generator 395. The output of tuning circuit 390 provides a Believed Value on lines 397 which is fed to maintenance checking circuits 399 which in turn provide a Believed Value output on line 396 and maintenance output signals on line 398.

The test method and system described above permits such tuning to be accomplished with realistic system values. When properly tuned, the system includes provisions for retention of the tuning coefficients such that if the input device comes into error or is inoperable, then the output of the system (the Believed Value) will stay in a reasonable range of value. By means of these adjustments, a Believed Value can be produced which compensates for a failing of one of the input components, so the output reading remains useable for the operator. Stated another way, the Believed Value is an output number derived from a system which is valid in the presence of a fault with one of the input components.

The Believed Value is generally produced for a given point for a specific condition or characteristic of the power plant, such as pressure, flow or fluid level. The basic difference between a Believed Value and a standard system value is that, due to the tuning circuit and the computation of the Believed Value against the set of input devices, a failure of one of the input devices will not produce an erroneous indication of a plant operating failure. In addition, the Believed Value is a number that does not have sudden shifts in it due to its input members taking sudden wide excursions. Connected to the output of the Believed Value tuning circuit is a test circuit for testing the Believed Value against acceptable quality standards, marking those deficient as requiring maintenance. The output of the test circuit includes maintenance signals for correcting the faulty input device. Also, a pre-processor can be connected between the input devices and the Believed Value tuning circuit for adapting the system to permit more than the given number, in this case, three, of inputs to be handled, such as n inputs. The output value of the system is a number that represents the best or most probable measurement for that value from an operating standpoint. For example, the steam pressure can be most probably represented as having the value X. The Believed Value is the number that the operator is supposed to believe and, therefore, should use in operation.

It is to be noted that the Believed Value technique is not analogous to the well known redundancy technique whereby all inputs must be identical and the system does not operate all inputs simultaneously. The conventional redundancy technique is one in which the identical lines are considered bi-stable as being in either the good or bad state and, a large excursion of one of the lines is totally ignored where the other two lines have the same values. Conventional techniques are very intolerant of non-matching dynamics of signals. By contrast, the Believed Value technique involves, the this case, three or more inputs or input devices which have reasonably compatible dynamics and the various measurement techniques associated with the three devices have time constants in the same order of magnitude, but has toleration for non-matching transients or dynamics. Also, according to the Believed Value technique, the tuning circuit takes into consideration variations in values of one of the input devices for every reading that the other input devices provide so that where such one input device should go faulty, the Believed Value will stay within its computed range.

Thus, the Believed Value technique includes the steps of tuning a filter circuit which is connected to receive signals from the input devices, such tuning being accomplished by calculating output values for the tuning circuit as a function of various values of the input devices over a range wherein an input device varies between its maximum and minimum excursions with the other two input devices being held to their expected values, such calculating includes weighing the effect of variations in value of one of the input devices on the output of the filter, and computing a Believed Output representative of the most likely value of a plant measurement and output of the tuning circuit, such Believed Value providing a reliable value of proper operating conditions under measurement whereby a fault in one of the input devices will not change the output of the system out of the range of the Believed Value. The system also includes a trigger mechanism and a maintenance, marking and bookkeeping system.

FIG. 16 shows the steps involved in the determination of the Believed Value. The first block of steps indicated as 400 is the basic Believed Value determination, the second block of steps labeled 410 is the post processing check required for reporting deviant inputs so that proper maintenance can be applied. After preprocessing has reduced the remaining values to three, they are processed by steps 400 and then by steps 410. Within the block of steps 400, the first step 401 is to prepare Averages of each pair of the three values. These are called Average one (1), Average two (2) and Average three (3). Average one (1) consists of the average of Values one and two. Average two (2) consists of the average of Values one and three. Average three (3) consists of the Average of Values two and three. Step 402 normalizes these averages by dividing each of them by a non-linear factor (NLF) which is one of the tuning coefficients described for this system. Step number 403 determines the absolute value of the differences between input Value one and two, Value one and three, Value two and three, and divides each of them by the non-linear factor NLF.

Step 404 defines the computation of weighting factor (WF) calculated for each average (401) and the corresponding normalized absolute difference (403) and the other tuning factor NLP, non-linear power. The denominator of the equation in 404 is computed by adding to one (1) the absolute normalized difference (403) raised to the non-linear power (NLP) and the result divided by the Average (401). The numerator of the equation is one. This equation (404) is repeated for each pair of corresponding Averages and Differences.

Step 405 sums each Average multiplied by its weighting factor for the numerator, and then divides that by the summation of the weighting factors to produce the Believed Value.

Block 410 in the post processing sorts out the transducers that require maintenance attention and designates them as Bad or Suspect and, if they do not require maintenance attention, marks them as good. This is accomplished by step (411) for calculating the absolute differential between Value one and the Believed Value previously determined (405), Value two and the Believed Value previously determined, and Value three and the Believed Value previously determined. In step 412, the two smallest of the absolute differentials are averaged and their associated values are marked as good. The average of these two smallest differentials is compared (413) with the non-linear factor and selects which ever of these numbers is the greater. This greater number is referred to as the test factor or TF. A further check is made to insure that the test factor (TF) has not exceeded five times the non-linear factor. Such a deviation indicates a broad discrepancy in the input readings and all are marked Suspect for a maintenance checking. In step 414, the largest or remaining of the absolute differences (411) is checked to see if it is greater than Z times the test factor (TF), Z being an adjustable tuning coefficient. If the absolute difference is greater than Z times the test factor, its associated Value is marked Bad and flagged for maintenance. In step 415, the largest absolute difference is again checked against Y times the test factor, Y being an adjustable tuning coefficient, and if it is found to be greater than Y times but less than Z times the test factor (TF), it is marked Suspect and again flagged for maintenance. If it passes both tests, the associated value is marked good in step 416 and the function has been accomplished.

Although the above description is directed to the preferred embodiments of the invention, it is noted that other variations and modifications will be apparent to those skilled in the art, and, therefore, may be made without departing from the spirit and scope of the present invention.

Claims

What is claimed is:

1. A method of producing a value which is most representative of a condition determined by a plurality of physical measurement input devices which are responsive to the condition which can change, the method comprising the steps of:

a. receiving signals from a plurality of input devices, the signals representing the values which are responsive to the condition;

b. averaging the value represented by each of the received signals with the value represented by each of the other received signals to derive a set of averages;

c. selecting a predetermined non-linear factor which corresponds to the probable disagreement between the received signals;

d. forming a normalized average for each of the set averages by dividing each average by the non-linear factor;

e. subtracting from the value represented by each of the received signals the value represented by each of the other signals to derive a set of absolute differences:

f. dividing each of the absolute differences by the non-linear factor to provide a first set of normalized differentials;

g. selecting a predetermined non-linear power which controls the degree of weighting for each signal as a function of its deviation from the other received signals;

h. raising each of the first normalized differentials by the selected non-linear power;

i. deriving a weighting factor for each average whose value is a function of its normalized average and its normalized differential raised by the selected non-linear power;

j. weighting each average by the weighting factor derived for that average; and

k. forming a composite of the weighted averages to thereby derive a value which is most representative of the condition.

2. A method in accordance with claim 1 in which the step of receiving signals from a plurality of input devices which are responsive to the condition comprises receiving signals representing at least three values which are responsive to the condition.

3. A method in accordance with claim 1 in which the step of receiving signals from a plurality of input devices which are responsive to the condition receiving at least two signals representing values responsive to the condition and receiving a signal representing a reference value which corresponds to the value related to the normal state of the condition.

4. A method in accordance with claim 1 in which the step of receiving signals from a plurality of input devices which are responsive to the condition comprises receiving a reference signal corresponding to a value which is substantially displaced in one sense with respect to the expected value of the condition and receiving another value displaced in the opposite sense from the expected value for providing a plurality of values where a plurality of values responsive to the condition are not available.

5. A method in accordance with claim 4 in which the step of receiving a reference signal corresponding to a value which is substantially displaced in one sense with respect to the expected value of the condition comprises receiving a reference signal approaching a zero level and in which the step of receiving another value displaced in the opposite sense from the expected value comprises receiving an additional signal approaching an infinite level.

6. A method in accordance with claim 1 and further comprising the step of selecting values to be received at least a portion of which have substantially corresponding transient response and forming the composite of weighted averages during the presence of transients in the values being received, the substantial correspondence in transient response of the values being received reducing the discrepancy of such values from the value representing the true condition.

7. A method according to claim 1 in which the step of weighting includes the step of multiplying each average by the weighting factor derived for that average.

8. A method according to claim 1 in which the step of forming a composite includes the steps of:

i. summing the weighting factors to form a composite weighting factor;

ii. summing the averages after each average has been multiplied by the weighting factor derived for that average; and

iii. dividing the sum of averages of step (ii); by the sum of weighting factor of step (i).

9. A method in accordance with claim 1 in which the step of deriving a weighting factor for each average comprises the steps of:

dividing each of the raised normalized differentials by its corresponding normalized average to form a set of ratios;

summing each of the ratios with a predetermined constant; and

inverting each of the summed ratios to thereby form the weighting factors.

10. A method in accordance with claim 9 in which said predetermined constant has a value equal to 1.

11. A method in accordance with claim 1 further comprising the step of tuning the forming of the composite of the weighted averages, step of tuning including:

repeatedly varying the output of one of said input devices over a likely range of values including a value representing a signal received from an input device which is in a failure mode while holding the outputs of the other input devices at appropriate levels;

for each repeated variation selected different non-linear factors and non-linear powers;

for each repeated variation comparing the characteristic of the composite of said weighted average with the desired characteristic of the value of the condition;

whereby the non-linear factor and the non-linear power result in a characteristic most representative of the desired characteristic can be derived.

12. A method in accordance with claim 1 and further comprising the steps of:

a. deriving the difference between the value representing each of the received signals and the composite of said weighted averages to form a second set of absolute differences;

b. averaging the two smallest absolute differences of said second set to form an average difference;

c. marking the received signals associated with the smallest differentials of the second set thereof as good;

d. determining the larger value of the average differential and the non-linear factor, the larger value being a test factor:

e. comparing the test factor with a predetermined multiple of the non-linear factor to determine whether the test factor is in excess of the predetermined multiple of the non-linear factor; and

f. additionally marking all received signals suspect for maintenance checking when the test factor is in excess of the predetermined multiple of the non-linear factor.

13. A method in accordance with claim 12 and further comprising the steps of:

a. selecting the largest absolute difference of the second set of absolute differences; and

b. comparing the selected largest absolute difference with a unique value which is a predetermined multiple of the test factor to determine whether the received signal related to the selected largest absolute difference of the second set is bad or has excessive discrepancy.

14. A method in accordance with claim 13 and further comprising the step of:

further marking a received signal with one of predetermined designations of good, bad and having excessive discrepancy from the value which is most representative of the condition, the step of marking being in response to the step of comparing the selected largest absolute difference with the unique value.

15. A method in accordance with claim 13 in which the unique value is a predetermined first multiplier of the test factor, the product of the first predetermined multiplier and the test factor defining an excessive discrepancy of a received signal from the value which is most representative of the condition.

16. A method in accordance with claim 15 and in which the step of further marking comprises marking the received signal related to the selected largest absolute difference of the second set as being bad.

17. A method in accordance with claim 16 and in which the step of further marking comprises marking the received signal related to the selected largest absolute difference of the second set as being suspect.

18. A method in accordance with claim 17 in which the unique value is a predetermined second multiplier of the test factor, the product of the second predetermined multiplier and the test factor defining an undesirable discrepancy which is less than an excesive discrepancy of a received signal from the value which is most representative of the condition.

19. Apparatus for producing a value which is most representative of a condition determined by a plurality of physical measurement input devices which are responsive to the condition which can change, the apparatus comprising:

a. means for receiving signals from a plurality of input devices, the signals representing the values which are responsive to the condition;

b. means for averaging the value represented by each of the received signals with the value represented by each of the other received signals to derive a set of averages;

c. means for selecting a predetermined non-linear factor which corresponds to the probable disagreement between the received signals;

d. means for forming a normalized average for each of the set averages by dividing each average by the non-linear factor;

e. means for substracting from the value represented by each of the received signals, the value represented by each of the other signals, to derive a set of absolute differences;

f. means for dividing each of the absolute differences by the non-linear factor to provide a first set of normalized differentials;

g. means for selecting a predetermined non-linear power which controls the degree of weighting for each signal as a function of its deviation from the other received signals;

h. means for raising each of the first normalized differentials by the selected non-linear power;

i. means for deriving a weighting factor for each average whose value is a function of its normalized average and its normalized differential raised by the selected non-linear power;

j. means for weighting each average by the weighting factor derived for that average; and

k. means for forming a composite of the weighted averages to thereby derive a value which is most representative of the condition.

20. An apparatus in accordance with claim 19 and further comprising:

a. means for deriving the difference between the value representing each of the received signals and the composite of the weighted averages to form a second set of absolute differences;

b. means for averaging the two smallest absolute differences of the second set of absolute differences to form an average difference;

c. means for marking the received signals associated with the smallest differentials of the second set thereof as good;

d. means for determining the larger value of the average differential and the non-linear factor, the larger value being a test factor;

e. means for comparing the test factor with a predetermined multiple of the non-linear factor to determine whether the test factor is in excess of the predetermined multiple of the non-linear factor; and

f. means for additionally marking all received signals suspect for maintenance checking when the test factor is in excess of the predetermined multiple of the non-linear factor.

21. An apparatus in accordance with claim 20 and further comprising:

a. means for selecting the largest absolute difference of the second set of absolute differences; and

b. means for comparing the selected largest absolute difference with a unique value which is a predetermined multiple of the test factor to determine whether the received signal related to the selected largest absolute difference of the second set is bad or has excessive discrepancy.