U.S. patent application number 11/258610 was filed with the patent office on 2006-08-10 for multiplexed autonomous sensors and monitoring system and associated methods.
Invention is credited to Marshall E. JR. Smith, Richard W. Stettler.
Application Number | 20060174682 11/258610 |
Document ID | / |
Family ID | 29254319 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060174682 |
Kind Code |
A1 |
Smith; Marshall E. JR. ; et
al. |
August 10, 2006 |
Multiplexed autonomous sensors and monitoring system and associated
methods
Abstract
A sensor monitoring system and associated methods are provide
that preferably include a plurality of sensors connected in
parallel across a single pair of wires that include resistances of
equal value placed in series between each sensor. This allows each
sensor to measure the voltage dropped between itself and the
monitoring system to determine its relative placement on the bus to
autonomously assign itself a number to delineate to the monitoring
system its relative location on the equipment or item being
monitored. The sensors modulate their internal resistance to change
the current on the bus to transmit their status to the monitoring
system.
Inventors: |
Smith; Marshall E. JR.;
(Eaton, FL) ; Stettler; Richard W.; (Winter Haven,
FL) |
Correspondence
Address: |
CARL M. NAPOLITANO, PH.D.;ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST, P.A.
255 SOUTH ORANGE AVE., SUITE 1401
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Family ID: |
29254319 |
Appl. No.: |
11/258610 |
Filed: |
October 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10345842 |
Jan 16, 2003 |
6962069 |
|
|
11258610 |
Oct 25, 2005 |
|
|
|
60349876 |
Jan 16, 2002 |
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Current U.S.
Class: |
73/1.01 ;
73/1.88 |
Current CPC
Class: |
G01D 3/028 20130101 |
Class at
Publication: |
073/001.01 ;
073/001.88 |
International
Class: |
G01D 18/00 20060101
G01D018/00 |
Claims
1. A monitoring system comprising: means for measuring a quiescent
signal provided by a sensor positioned within an environment having
a first temperature; means fro measuring a dynamic signal from the
sensor during operation of the sensor at a second temperature;
means for comparing the quiescent signal to the dynamic signal for
determining a change therebetween; and means for modifying a gain
in the dynamic signal based on the change for providing a corrected
dynamic signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/345,842, filed Jan. 16, 2003, which claims the benefit of
U.S. Provisional Application No. 60/349,876, filed Jan. 16, 2002,
the disclosures of which are hereby incorporated by reference
herein in their entireties, and all commonly owned.
FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
sensor monitoring, and more particularly to a system of
interconnecting and monitoring a plurality of sensors with each
sensor having autonomous access to a data communication medium
independent of other devices.
BACKGROUND OF THE INVENTION
[0003] Most machinery or industrial equipment employ sensors for
status monitoring or control. Usually, the machinery is relatively
complex and more than one sensor is employed to sense more than one
parameter, event, or situation. These sensors are connected to
monitoring circuits and together or in combination form a sensor
monitoring system. Primary goals for these sensing systems are that
they be reliable and inexpensive to apply. Some widely used methods
of maximizing reliability are to create sensors with the least
amount of components to reduce failure rates, the least amount of
interconnections possible to reduce wiring faults, and to provide
some form of self-diagnostics to determine the sensor's operational
status to separate sensor failure from other system problems.
Reducing the number of components and the number of
interconnections also serves to reduce the overall cost of applying
the sensors. Other methods also exist to reduce the application
cost while not reducing reliability. A method of reducing sensor
application cost while increasing reliability is to connect the
sensors in a multiplexing scheme where possible to use a minimum
amount of interconnects and external wiring.
[0004] Sensors generally have one of three types of outputs: an
analog output proportional to the quantity or relative quality of a
sensed parameter or to the position of an object or objects, a
switched output that is generated when a sensed parameter or the
position of an object or objects ranges outside a preset limit, and
a digital output that is usually an encoded signal proportional to
the analog measurement of the parameter being sensed or to the
position of an object or objects. Four possible applications exist
wherein more than one of these sensors is applied that determine
whether the sensors can be multiplexed and how they can be so
connected.
[0005] The first application is for machinery that is structured so
all the events are either mechanically interconnected or otherwise
controlled so that no event that is being monitored occurs at the
same time as any other event. This is known as mutually exclusive
event monitoring. A primary example of a type of machine that uses
this scheme is an internal combustion engine. On most engines up to
eight cylinders, the operation of each cylinder is synchronized to
all the others through mechanical linkages in a manner such that
only one cylinder is generating power at any time. A system
monitoring the status of the fuel injectors in the individual
cylinders of these engines would be a mutually exclusive event
monitoring system. If an event occurs, the monitoring system can
use engine timing information such as the rotational position of
the crankshaft to determine in which engine cylinder the event is
occurring. All sensors can therefore be multiplexed together with
no regard to whether any sensor signal will conflict with the
signal from another sensor.
[0006] A second situation exists wherein the arrangement of
machinery is unstructured so any single event can occur at any time
regardless of the status of any other event. This situation is
known as real-time event monitoring. In real-time event monitoring,
there are two situations in which the sensors are applied. A first
situation is delineated by whether the events are variable in
nature and contain information that must be decoded. Analog or
digital sensors monitor these events. A second situation exists
where the information desired is whether any one of a plurality of
events is simply beyond a preset limit or exceeds a preset
parameter. These events are monitored with switched output
sensors.
[0007] In a first real-time event monitoring situation, the
important information about the events being monitored are the
actual details about the event itself, for instance, when and how
far any single item moves. This is known as discrete event
monitoring. A prime example of this system is the monitoring of
individual wheel speed sensors on an automotive antilock brake
system. In the case of wheel spin or loss of traction, any or all
of the individual wheels can have different speeds. The system must
know which wheel has a particular speed to adjust the braking force
on that wheel only. Each sensor must be monitored separately to
determine that particular wheel's speed.
[0008] In a second real-time event monitoring situation the sensor
monitoring system simply delivers information relating to the
status of a collection of events, for instance, whether all items
being monitored are in an appropriate or safe position. This is
known as one-of-any alarm monitoring. A primary example of this
type system is the monitoring of the position of the doors on an
automobile. The system delivers an alarm if any door is open.
Information about which door is open, or how far it is open, is not
needed to generate the alarm condition. These sensors can be
multiplexed together, as long as two conditions exist. The first
condition is that the alarm signal is not lost if more than one
sensor transmits information at the same time. For instance, in the
door open alarm situation, if more than one doors is open, the
signals from the sensors should add in value and not cancel each
other out. A second condition exists when either the particular
sensor with the alarm condition is not delineated to the monitoring
system, or when the sensor generates some sort of signal so the
monitoring system will know specifically which alarm is being
generated. It is a common practice in the one-of-any alarm
monitoring systems to not delineate the specific location of the
alarm but to simply announce that at least one alarm condition
exists, in favor of reduced system complexity. The usual
alternative to this least expensive monitoring system is to program
each sensor with a specific digital signal that identifies the
particular sensor generating the alarm. This method, however,
requires that the sensors not transmit information
simultaneously.
[0009] A further method of multiplexing sensors that generate
digital signals is to assign each sensor a unique number that
delineates the sensor's position and function. This is called a
multiplexed digital sensor system. The sensor transmits these
numbers along with a number denoting its status either upon a
specific event, on regular intervals, or when polled by the sensor
monitoring system. There are three methods of assigning unique
numbers to each sensor. In the first method, a unique number is
assigned during manufacture of the sensor. This is usually
accomplished by individually encoding digital numbers into
semiconductor material used to generate the sensor circuitry. A
second method is to provide a series of switches that the end user
programs to individually assign a unique number to each sensor. A
third method is to allow the end user to assign a unique number to
each sensor by programming methods. Each method is relatively
expensive to employ. Assigning a unique number during manufacture
requires complex procedures such as vaporizing metal traces with a
laser or burning open diode junctions with high voltages. Employing
a series of switches or other programming means for the end user to
uniquely assign numbers increases the size and complexity of the
sensor, increasing cost and reducing reliability. These methods
also require that the end user or monitoring system keep track of
the numbers assigned so no two sensors have the same number, and so
replacement sensor can be assigned the same number as the sensor
being replaced.
[0010] It is now recognized and addressed by the present invention
that an important distinction exists between these four forms of
sensor monitoring as it applies to the wiring of the sensors.
Sensors used in the least expensive one-of-any alarm monitoring
where the particular sensor generating the alarm is not identified,
and sensors used in mutually exclusive event monitoring can have
analog outputs and can have their outputs connected to the same
point electrically because either the events being monitored can
only occur independently of each other, or because the information
desired is whether any event among a set of possible events is
occurring. The determination of which event is occurring can be
derived by some other means such as the timing of related events,
or the determination of which event is occurring is not as
important as the determination of the fact that some specific event
is occurring. The discrete event monitoring system and multiplexed
digital sensor system cannot use analog signals connected in this
simplest multiplexing scheme without some method of insuring that
the information delivered by any one sensor is not superimposed
over the information delivered by any other sensor. A common
practice for these discrete event monitoring systems is to either
connect analog outputs separately at the monitoring system, or to
digitize the signals and have the sensors transmit the data
separately in time so no sensor signal interferes with any other
sensor signal.
[0011] It is further recognized and addressed by the present
invention that a significant problem in sensor systems is that a
sensor may itself fail and indicate falsely that either an alarm
condition exists or that an event is or is not occurring,
regardless of the true status of the system being monitored. It is
imperative in some situations that the sensor monitoring system is
capable of diagnosing the sensors to determine if a signaled event
or problem is due to system problems or simply due to sensor
failure. Knowing that a problem is due to simple sensor failure may
mean the difference between being able to run the system in a
limited mode or having to shut it down, or in operating dangerously
when an alarm condition exists that is not being signaled by a
broken sensor.
[0012] Most prior art position and proximity sensor devices
transmit information in one of three ways. Analog position sensors
generate an analog signal proportional to a specific parameter
being monitored, such as the temperature or the position of one or
more objects. Digital proximity sensors generate one or more
digital pulses when one or more events occur such as a temperature
going above or below a specific set point, or an object moving
beyond a specific position. Digital encoder sensors generate
digital information concerning the position of an object, the
occurrence of an event, or the status of a situation.
[0013] Prior art analog position sensors sense the location of
objects by sensing the presence of or the relative amount of
specific items or materials within their sensing range. Various
examples of the technology employed in these sensors are inductive,
capacitive, or magnetic sensors. The analog position sensor output
is proportional to the position or movement of the object being
monitored. These sensors usually rely on the generation of static
electromagnetic or magnetic fields and the subsequent dynamic
change in the field caused by the movement of the object being
monitored. The static fields generated or otherwise used by these
sensors are usually at least an order of magnitude larger than the
dynamic change in the field caused by the object's movement. These
sensors therefore usually transmit large static DC signal offsets
and smaller dynamic signals as an object is monitored. This is
because there is usually a significantly larger amount of similar
nonmoving material in the sensing range of the sensor. For
instance, small moving valves are usually surrounded by large rigid
housings. This is especially true of magnetic sensors because they
usually rely on large, high strength magnets to generate the static
field. It is yet further recognized and addressed by the present
invention that there is a significant problem is encountered with
these sensors if they generate signals using current modulation.
The usually quite large static offset signal produces a
correspondingly large current, and the dynamic signal as the target
moves is usually quite a bit smaller. The large static current
causes remote monitoring swamping resistors to drop a large portion
of the applied voltage that is used to power the sensor. Also, the
monitoring equipment must be capable of ignoring or eliminating the
large static offset and amplifying the smaller dynamic signal.
[0014] Prior art pulse output proximity sensors generate one or
more digital on/off pulses that change state when an object moves
between one or more defined positions or moves toward or away from
some preset position. These sensors contain output-switching
comparators with preset thresholds and hysteresis. Usually, the
sensor must be placed in a specific position in relation to the
object being sensed to allow the comparators to switch at a point
approximately halfway between the extremes of the object's range of
movement. It has also been recognized and addressed by the present
invention that unless complex compensation circuitry is added to
the sensor, the timing of these output pulses in relation to
specific object movement can vary significantly from one sensor to
the next or from one event to the next because of tolerances in
mechanical and electrical components due to changes in electronic
devices in the sensor due to aging or temperature changes. A
significant advantage is realized in the application of these type
sensors if they are produced with the ability to reprogram specific
set points independently of the position of the sensor relative to
the target.
[0015] A problem with the multiplexing of these switched output
sensors is that some method must be employed to allow the
monitoring system to determine which sensor is in the alarm state
if this information is needed. Usually, this is done with each
sensor transmitting a digital number delineating its position or
function. This greatly complicates the sensor, and requires that
each sensor be given a unique number during manufacture or during
initial installation.
[0016] Prior art digital encoder sensor outputs also cannot
transmit at the same time other sensors are transmitting
information. This may be ameliorated somewhat if the information is
only transmitted after all other sensors have transmitted their
information, usually after the event being monitored is occurring.
This usually precludes real-time monitoring of these sensors in a
multiplexed arrangement. Connecting these sensors to a single
interconnection point requires that some method be employed to
prevent them from transmitting information at the same time.
[0017] It has been found that semiconductor devices such as the
three prior art sensors above are usually very susceptible to
output changes due to changes in temperature. Temperature changes
can change the gain of the analog position sensor and can change
the response level and pulse timing of the digital proximity sensor
and digital encoder. Also, extreme temperatures can destroy or
damage them. Prior art sensor monitoring systems do not usually
contain temperature compensation for extreme changes in sensor
output as a result of temperature changes nor do they supply any
indication that the temperature is above a dangerous level.
[0018] Two-wire sensors are connected via two wires and generate
signals by modulating the amount of current passing through a
remote resistor connected in series between the sensor and a remote
monitoring circuit connected to these two wires. The sensor signal
is developed into a voltage signal across the resistor. The voltage
across the resistor becomes the signal from the sensor. Two-wire
technology is less expensive and more reliable than technologies
using more wires. Two-wire connection of the three main type of
prior art sensors, however, is made difficult by various problems
specific to the type of sensor being employed. The smaller dynamic
signal must be amplified more to overcome noise. The analog output
position sensor's large DC offset through the monitoring resistor
wastes power and reduces effective power supply voltage to all
sensors. The proximity sensor and digital encoders generate digital
pulses that must be transmitted separately from the pulses from any
other sensor and some manner of identifying which sensor is
generating the information must be employed.
[0019] These sensors may be multiplexed, or a multiplicity of
sensors can be connected in parallel to the same set of two wires,
as long as the following criteria are met:
[0020] First, in the case of mutually exclusive event monitoring,
mechanical or electrical limitations on the system preclude any of
the monitored events from occurring at the same time. In this case
we usually know which event should be occurring at any one time and
know therefore that the sensor outputting a signal has to be
monitoring an event of particular interest. A prime example is the
monitoring of the operation of fuel injectors on internal
combustion engines. The engine controller or fuel pump may initiate
the injections. We know when a particular injection from a
particular injector should occur, within a window of time. The
sensors can be made very inexpensively because complex circuitry is
not required to prevent the sensors from generating conflicting
information at the same time. These sensors can generate analog
signals, alarm pulses, or digital information without generating a
signal at the same time as any other sensor.
[0021] Second, the situation may be such that we only want to know
that all the sensors are in a particular desired situation. The
sensor only transmits information if the situation changes at any
one of the monitored stations. It does not matter which sensor has
the problem, or that more than one sensor has an alarm situation.
This is known as monitoring one-of-any alarms. A prime example is a
network of door sensors.
[0022] Accordingly, there is a need for a sensor monitoring system
that overcomes the limitations of prior art sensors and monitoring
systems when monitoring mutually exclusive events or one-of-any
alarm conditions.
SUMMARY OF THE INVENTION
[0023] With the foregoing in mind, the present invention
advantageously provides a sensor or sensor system that overcomes
the noise and uncertainty of the digital proximity and encoder
sensors. According to the present invention, a specially adapted
analog sensor preferably is used to accomplish this. This sensor is
modified to eliminate the large DC offset signal and amplify the
resultant dynamic signal as much as possible to overcome noise. The
quiescent current drawn by the sensor is determined at a known
temperature, and compared to the dynamic signal. Any changes in the
quiescent current can then be tracked to determine sensor
temperature, and to determine and compensate for equal changes in
the gain of the dynamic signal gain. For instance, in an
application for monitoring engine fuel injectors, the temperature
of all components is known before initial start of the engine if
the car has not been started for a significant length of time. The
current drawn by the sensors is compared to the level of the
dynamic signals immediately after the vehicle is started. After the
engine is running, changes in the quiescent current indicate
consequent changes in temperature. The percentage of change of the
quiescent current is then used to modify the gain of the dynamic
signal to keep sensor gain constant over its temperature range. A
further determination of the temperature of the sensors is possible
when the sensors are placed in the calibrate mode. At this time,
compensation is provided for the large static offset by subtracting
an equal voltage in a differential amplifier. The sensor starts at
zero volts and steadily increases the compensation one discrete
step at the time until the compensation voltage equals the offset
voltage. During this time the sensor transmits a pulse each time
its internal clock generates a command to change the compensation
voltage. The levels of this clock pulse are preset and change only
with temperature. The sensor monitoring system can compare the
levels of these pulses during calibration to also determine sensor
temperature. These sensors preferably are multiplexed on two wires
to reduce wiring cost and complexity.
[0024] The present invention advantageously a sensor monitoring
system and associated methods are provide that preferably include a
plurality of sensors connected in parallel across a single pair of
wires that include resistances of equal value placed in series
between each sensor. This allows each sensor to measure the voltage
dropped between itself and the monitoring system to determine its
relative placement on the bus to autonomously assign itself a
number to delineate to the monitoring system its relative location
on the equipment or item being monitored. The sensors modulate
their internal resistance to change the current on the bus to
transmit their status to the monitoring system. When the sensor is
manufactured, a number may be assigned to the sensor that denotes
the sensor's function and is transmitted to the monitoring system
when the status of the sensor changes. The sensors monitor the
applied voltage that changes as a sensor transmits data to prevent
any two sensors from generating signals at the same time. The
monitoring system places a specific voltage onto the bus to place
the sensors into either an enumeration mode wherein each sensor
assigns itself a unique number, or a calibrate mode wherein each
sensor determines and adjusts specific information based on its
operation and input parameters, or a run mode wherein each sensor
monitors its input parameters and transmits information as
required. Each sensor draws a specific amount of quiescent current
when the enumeration voltage or the calibrate voltage is generated.
The enumeration voltage is generated to allow each sensor to
determine its relative position on the bus and to assign itself a
relative position number. The calibration voltage is generated to
allow the sensors to calibrate themselves to eliminate static
offset voltages caused by the use of internal or external fields
generated to monitor the movement or position of objects. The run
voltage is generated to allow the sensors to monitor the output
line and transmit information autonomously without any two sensors
transmitting at the same time. A series of digital numbers denoting
which sensor is to be calibrated may also be transmitted by the
sensor monitoring system along with digital numbers setting
parameters in the sensor to customize its operation. This would
allow it to change specific parameters such as set points for
switched outputs, or to set gain or offset levels. During
calibration, the sensors draw a specific amount of quiescent
current that changes in proportion to the sensor temperature that
the monitoring system uses to determine the overall system
condition. During the calibration sequence, particular position or
proximity sensors may also generate a specific quantity of clock
signals corresponding to the level of static offset signal commonly
encountered in their application. The number of clock signals
convey to the monitoring system the strength of background fields
used to generate information in the sensor. The relative strength
of the clock pulses convey to the monitoring system the gain of the
sensor components and the relative resistance of the
interconnections between the sensor and the monitoring system. The
monitoring system may also monitor the levels of other digital
pulses generated by the sensors to determine the integrity of the
interconnection system and to determine the relative position of
the sensor transmitting the information. A lowest voltage is
generated to place the sensors in a run mode to allow them to
monitor their respective functions and to transmit information to
the monitoring system. Voltages higher in value than the run
voltage are generated by the monitoring system as digital codes to
set various sensor parameters such as gain and switching set
points. The sensors transmit their data as increases in current.
This serves to cause the voltage to drop as the data is being
transmitted. This drop in voltage below the run level inhibits the
other sensors from also transmitting data until the run voltage
returns to its normal level. The relative current drawn by the
system and the relative voltage level of these digital pulses will
be changed as the resistance of interconnects changes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Some of the features, advantages, and benefits of the
present invention having been stated, others will become apparent
as the description proceeds when taken in conjunction with the
accompanying drawings in which:
[0026] FIG. 1 is a schematic block diagram of a sensor having a
monitor according to the present invention;
[0027] FIG. 2 is a schematic block diagram of a sensor system
having a monitor according to the present invention; and
[0028] FIG. 3 is a graph of value versus time of mutually exclusive
event waveforms of a sensor system according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings that
illustrate preferred embodiments of the invention. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout, the prime notation, if used, indicates similar
elements in alternative embodiments.
[0030] As shown in FIGS. 1-3, preferred embodiments may include a
sensor monitoring system and sensors that connect via a two-wire
multiplexed system. Provision is made to allow the sensors to
assign themselves unique numbers based on their relative position
on this bus. Provision is also made to preclude any sensor from
transmitting data while any other sensor is already transmitting.
Sensors may have analog outputs, switched outputs, or digital pulse
train outputs. Position sensors or other sensors with large static
DC offset signals have provisions to eliminate the large static DC
signal and amplify the dynamic event signal. The sensor monitoring
system also monitors the relative signal levels of the sensors and
transmits a diagnostic signal if they fall out of a specified
range. Various sensors with large static DC offset signals and
relatively small dynamic output signals are also conditioned to
reduce the offset and amplify the dynamic portion of the signal to
improve efficiency and reduce noise.
Sensor/Monitor Operation Procedure
[0031] Initial Power-Up
[0032] Monitor goes into sensor count mode, sets power supply
voltage high enough to place first sensor in enumerate mode (7
VDC). First sensor shuts off its output, monitor senses decrease in
current, counts first sensor.
[0033] Monitor continues to steadily ramp up power supply voltage.
Voltage increases to a level necessary to put next sensor into
enumerate mode (7.1 VDC)
[0034] Next sensor shuts off output, monitor senses decrease in
current, counts next sensor.
[0035] Procedure repeats from step 3 till no change in current
occurs.
[0036] The monitor records the number of sensors; if the number of
sensors is same as last power-up, procedure is ended.
[0037] If the number of sensors is less than at the last power-up,
the monitor generates an alarm. Operator repairs bad or missing
sensor or resets the monitor alarm if a sensor has been removed.
Procedure is repeated from step 1.
[0038] If number of sensors is more than last power-up, monitor
records new number and shuts off power to reset the sensors.
[0039] Monitor sets power supply output high enough to place all
sensors in enumerate mode.
[0040] (7 VDC+(0.1* (# of sensors minus one)).
[0041] After brief period, all sensors enumerate and set their
calibrate and run voltages to compensate for voltage drops across
their respective series resistors.
[0042] (Sensor calibrate is 6 VDC+(0.1* sensor #)
[0043] (Sensor run is 5 VDC+(0.1* sensor #)
Calibrate Mode For Position Sensors With Large Offset Only
[0044] Monitor sets power supply to calibrate voltage level of
first sensor in line.
[0045] First sensor begins a calibration; offset goes to zero as
clock pulses are transmitted.
[0046] All other sensors sense drop in voltage as first sensor
transmits; sensors place themselves in hold mode.
[0047] Monitor counts clock pulses and stores total number.
[0048] When output is zeroed, sensor clock output stops decreasing
and varies above and below a fixed point.
[0049] Monitor stores total number of clock pulses.
[0050] Monitor compares present level to previously stored level,
if present.
[0051] If present level significantly different from previous
level, monitor generates an alarm.
[0052] Monitor increases calibrate voltage to level needed to
calibrate next sensor.
[0053] Next sensor begins calibration, offset goes to zero as clock
pulses are transmitted
[0054] Repeat from step 3 until last sensor reached.
Run Mode
[0055] Monitor to run mode, voltage to 5 VDC+(0.1 VDC*# of sensors
minus one)
[0056] Monitor determines initial system temperature if available
monitor compares sensor output pulses or quiescent current to
values taken at a known temperature, stores value.
[0057] Monitor generates an alarm if sensor output indicates
extreme temperature.
[0058] Repeat steps 1 through 4 as needed.
[0059] Sensors generate data by modulating the current. As the
current increases through the signal resistor, the supply voltage
goes down. Each other sensor is inhibited until the bus voltage
returns to the run level for a short period of time.
Set Point/Gain Set Mode
[0060] Monitor generates sensor number and set points or gain
information digitally by increasing the voltage. Sensors know that
monitor is transmitting information because voltage is increasing
above run level. All sensor outputs shut off until bus returns to
run level.
[0061] FIG. 1 schematically illustrates a complete monitoring
system with a monitor 300 and a single sensor 100. A series of
sensors 100 are shown connected through series resistors 206 to
monitor 300 in FIG. 2. Monitor 300 supplies power to sensors 100
through two wires, positive wire 202 and negative wire 204. Sensors
100 transmit their output signal by controlling the resistance of
current modulator 142. This current modulation is transformed into
a voltage sensor signal 304 in monitor 300 when it passes through
signal resistor 302. This signal is then processed as needed by
mode controller and decoder 310 and transmitted to external
equipment through output 312.
[0062] Sensor 100 contains a logic control 102 that senses the
applied voltage and selects functions based on the levels of these
voltages. Monitor 300 generates commands and sets a mode for the
sensor 100 by increasing the voltage level on the sensor 100 input
above a nominal value which is run voltage 308. Sensors 100
generate information and transmit signals by increasing the current
through current modulator 142, resulting in voltages lower in value
than run voltage 308. In this manner, logic control 102 determines
that information is coming from monitor 300 when the voltage
increases in value, and that information is coming from another
sensor 100 connected to the bus when the voltage decreases in
value. Monitor 300 selects one of four functions by modulating the
voltage level between positive wire 202 and negative wire 204. When
monitor 300 enters the enumerate mode, it generates a steadily
increasing voltage across the bus. Logic control 102 compares the
voltage generated by monitor 300 to an internal reference. When
this voltage goes higher than a threshold voltage required to place
it in the enumerate mode, it opens run switch 140 to remove any
signal from the bus. Monitor 300 determines when this occurs as the
current decreases in value and then steps up the voltage by a
discrete amount and again waits for the current to drop. If there
are other sensors 100 attached to the bus they will likewise turn
off their output and lower the bus current resulting in increasing
sensor signal 304. This procedure will be repeated until no more
current drops are sensed. The monitor counts each current drop and
therefore knows how many sensors 100 are connected to the bus.
Monitor 300 then removes all power from the bus for a short period
of time to reset all the sensors 100. It then applies a voltage on
the bus that is high enough in value to place all sensors 100 into
the enumerate mode through all the series resistors 206. For
example, assume the voltage required to place the sensors in the
enumerate mode is 7 Volts DC, and that each series resistor drops
0.1 Volt. Monitor 300 first places 7 Volts on the bus. The sensor
connected to the first position on the bus closest to monitor 300
has no series resistance, so it receives this 7 Volts and goes into
the enumerate mode. It drops its current and monitor 300 senses
this. Monitor 300 then changes the voltage to 7.1 Volts. The second
sensor in line then receives 7 Volts and goes into the enumerate
mode. This process repeats until the last sensor 100 is reached at
which time the current no longer decreases and the monitor 300 then
knows how many sensors 100 are connected to the bus. Monitor 300
then adjusts the enumerate voltage to the appropriate value needed
to enumerate the last sensor 100 on the bus, and the sensors 100
then sense their applied value and enumerate themselves based on
this value. Logic control 102 does this by generating the sensor
number onto enumerate bus 108 and thereby placing it in number
storage 112 after sensor voltage has remained steady for a
significant length of time.
[0063] After the enumeration process is completed, monitor 300 then
places the sensors 100 into the calibrate mode by decreasing the
applied voltage on the bus to an intermediate level.
[0064] In FIG. 3, there is shown a typical set of waveforms for
position sensors using static electromagnetic fields for operation.
The static electromagnetic field generates a static DC offset 004
shown along with a dynamic event 002. Both signals are shown in
relation to their relative values. Note that the dynamic event 002
is much smaller in value than the static DC offset 004. Below these
waveforms is shown a desired sensor output signal. Note that now
the event 002 has been converted into an amplified dynamic signal
006 and that the static DC offset 004 has been reduced to a very
low value quiescent current 008.
[0065] The events 002 shown are a series of mutually exclusive
events 002 with the same offset and resultant signal conditioning.
Note that none of the events occur at the same time.
[0066] An additional temperature diagnostic capability is realized
when the sensors 100 are in the run mode if the temperature of the
system is known at some point in time. The relative levels of
signals from the sensors 100 can be programmed to increase in
direct proportion to the temperature of the sensor. Monitor 300 can
sense these changes and generate an alarm if a signal level
increase indicates that the temperature of the system or of the
sensors is rising beyond a specific level. By the same manner,
interconnect problems for the sensor 100 or with series resistors
206 will cause sensor 100 signal levels to decline. Monitor 300 can
also generate an alarm if these signals fall below a specific
level.
[0067] This concludes the teaching of the preferred embodiments.
Note however that in many different situations wherein specific
types of sensors may be connected in this system, various
simplifications of the preferred embodiments may be realized to
reduce complexity and cost and improve reliability. For instance,
if a system of similar sensors 100 is utilized in a system
consisting only of mutually exclusive events, specific functions
such as enumeration and function identification do not have to be
performed. The monitoring system will know which event is occurring
in time, and the functions will all be the same. Likewise,
monitoring of the clock output during the calibrate phase would not
have to be performed, as long as the sensors output is monitored
for changes in level to perform diagnostic checking. Similarly,
systems using one-of-any alarm sensors would also not require
enumeration or function identification. The monitoring system would
know from the relative pulse levels how many series resistors the
signal passes through from the corresponding level of these
pulses.
[0068] It should also be noted that all the features of the
preferred embodiments may be applied to sensor monitoring equipment
connected to single sensors with more than two wires. For instance,
sensors that deliver information continuously could be connected
with a third wire for a voltage output without substantially
deviating from the preferred embodiment by simply connecting the
current modulator to a third wire and using it as a voltage
generator. Sensor enumeration would not be required in this
situation, and diagnostics could be performed without the
additional series resistors by simply monitoring the output
level.
[0069] As described above and as illustrated in FIGS. 1-3, the
present invention advantageously provides a multiplexed two-wire
sensor and sensor monitoring system for any number or combination
of sensors, autonomously enumerated sensors, and a sensor
monitoring system. The present invention also advantageously
provides a sensor and monitoring system with sensor function
identification, a p-Position sensor and monitoring system with
output offset reduction for reduced power and reduced noise, a
position sensor and monitoring system with output offset reduction
with counted clock pulses output for electromagnetic field
diagnostics, and a one-of-any alarm sensor and monitoring system
with alarm position detection.
[0070] The present invention additionally advantageously provides a
mutually exclusive event sensor and monitoring system with two-wire
connection, a sensor and monitoring system with remote gain, set
point, or other calibration setting, a sensor and monitoring system
with sensor temperature monitoring and alarm, a sensor and
monitoring system with output queuing system based on sensing of
lowered voltages as another sensor transmits, and a sensor and
monitoring system with sensor position detection based on voltage
dropped across series resistors as the sensor transmits pulses or
switched outputs.
[0071] The present invention still also advantageously provides a
sensor monitoring system with sensor interconnect diagnostics based
on voltage dropped across bad connections, a sensor monitoring
system with sensor output level diagnostics to detect failing
sensors based on voltage dropped across series resistors, a sensor
monitoring system with multiplexed analog, switched level, and
digital pulse output sensors, a sensor monitoring system with
multiplexed sensors that generate a quiescent output when placed in
enumeration mode for determination of the number of sensors
connected to the bus, a sensor monitoring system utilizing
increased voltage levels to place the sensors in various modes of
operation, and a sensor monitoring system utilizing decreased
voltage levels to prevent any two sensors from transmitting at the
same time.
[0072] In the drawings and specification, there have been disclosed
preferred embodiments of the invention, and although specific terms
are employed, the terms are used in a descriptive sense only and
not for purposes of limitation. Further, it is understood that that
various modifications and changes may be made within the spirit and
scope of the invention without departing from the spirit and scope
of the present invention as set forth in the appended claims.
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