U.S. patent number RE31,089 [Application Number 06/220,626] was granted by the patent office on 1982-11-23 for transducer system for continuous monitoring liquid levels in _storage tanks and the like.
This patent grant is currently assigned to Chevron Research Company. Invention is credited to John S. Adamson.
United States Patent |
RE31,089 |
Adamson |
November 23, 1982 |
Transducer system for continuous monitoring liquid levels in
_storage tanks and the like
Abstract
The liquid level within a storage tank network is continuously
monitored by a transducer system of the present invention formed
essentially of MSI's (Medium Scale Integrated Chips) including a
differential pressure (dp) cell in circuit with a digital volt
meter (DVM) which, in turn, is connected to a series of look-up
ROM's (Read-Only Memories). In operation and as a function of dp
cell output level, DVM is continuously applying BCD signals to the
ROM's, such signals being proportional to liquid level. The ROM's
retain, in memory, the Gray code translations of the BCD input. The
ROM's are then periodically accessed via an analog multiplexer
controlled by an oscillator/ripple counter to provide corresponding
microcircuit level signals at the output of a 7-segment
decoder/driver. Thereafter, the microcircuit signals are
regenerated--at levels compatible with conventional MARK-SPACE tank
gauging systems--using an isolation/driver network in circuit with
the 7-segment decoder/driver. The aforementioned system is
initiated by a MARK-SPACE interrogation signal and has special
utility in digitally monitoring product/source levels within
source/product storage tank networks associated with an oil
refinery and/or a chemical complex.
Inventors: |
Adamson; John S. (La Habra,
CA) |
Assignee: |
Chevron Research Company (San
Francisco, CA)
|
Family
ID: |
26915034 |
Appl.
No.: |
06/220,626 |
Filed: |
December 29, 1980 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
854917 |
Nov 25, 1977 |
04194177 |
Mar 18, 1980 |
|
|
Current U.S.
Class: |
340/870.19;
340/618; 340/870.24 |
Current CPC
Class: |
G01F
23/18 (20130101) |
Current International
Class: |
G01F
23/14 (20060101); G01F 23/18 (20060101); H04Q
009/14 (); G08C 019/16 () |
Field of
Search: |
;340/870.19,870.24,152T,618 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yusko; Donald J.
Attorney, Agent or Firm: Newell; D. A. Keeling; Edward J.
Messner; H. D.
Claims
What is claimed is:
1. Transducer system for generating a digital code indicative of
liquid level within a storage tank or the like, upon receipt of a
square wave interrogation signal from a transmitter/receiver of a
tank gauging system located at a central station remote from said
storage tank but electrically connected to said transducer system
through an INTERROGATION, a MARK and a SPACE line of said tank
gauging system, comprising:
(a) means for providing a series of input signals representative of
liquid level within said tank, said means including a digital volt
meter (DVM) in circuit with a series of look-up read-only-memories
(ROM's);
(B) I/O network for receiving said interrogation signal and
connected to said DVM for generating a reset signal therefrom in
response to said interrogation signal;
(C) an oscillator/ripple counter formed essentially of MSI's
connected to said DVM and including at an input, a network for
receiving said reset pulse from said DVM, said oscillator/ripple
counter generating, in response to said reset pulse, sets of square
wave pulses of differing repetition rates and pulse widths;
(D) a multiplexer and multi-segment decoder/driver means connected
to each other and to (B) responding to selected sets of said square
wave pulses to generate a synthetic digital code indicative of
liquid level at microcircuit signal levels at an output means of
said decoder/driver means;
(E) isolatordriver means having one or more inputs connected to
said decoderdriver means of (D, and one or more output means
connected to said MARK and SPACE lines controllable as a function
of said synthetic digital code to drive said MARK and SPACE lines
between tank gauging operating potentials for generating said
digital code of interest at said central station whereby said
liquid level condition within said storage tank can be
indicated.
2. The transducer system of claim 1 in which an initial first
generated set of square wave pulses by (C) is characterized by a
repetition rate higher than those of subsequent sets of square wave
pulses, for enabling an input of said multi-segment decoder/driver
means of (D) at said same repetition rate, and generating said
synthetic digital code at microcircuit signal levels.
3. Transducer system of claim 2 in which said enabled input of said
decoder/driver means of (D) is the BLANK-ing input of a 7-segment
decoder/driver.
4. The transducer system of claim 2 in which each subsequent set of
generated sets of square wave pulses provide in combination a
series of address commands at input means of said decoder/driver
means of (D) whereby X-in-16 particular address command per
interrogation cycle enables said decoder/driver means in circuit
with MARK line through said switching transistor means, and Y-in-16
address commands per cycle enable said SPACE line where X and Y are
whole numbers and X+Y=16, and whereby said synthetic code
indicative of liquid level is generated.
5. Transducer system of claim 4 in which said input means of said
decoder/driver means of (D) is the 2.degree. bit input of a
7-segment decoder/driver.
6. The transponder network of claim 4 in which each subsequent set
of generated sets of square wave pulses provide in combination a
series of multi-bit address commands for said multiplexer means of
(D) whereby output lines thereof are placed in alternately circuit
with said ROM's to receive synthetic code of interest.
7. Transponder system of claim 6 in which said logic output lines
connect to a 2.degree. bit data input of a 7-segment
decoder/driver.
8. Transponder system of claim 7 in which 2.sup.1 and 2.sup.2 bit
inputs of said 7-segment decoder/driver are continuously HI, and
the 2.sup.3 bit input is continuously LOW whereby first and second
outputs of said 7-segment decoder/driver oscillates between binary
equivalents of a imaginary LED display of the number "6" or "7",
depending on HI,LOW state of said 2.degree. bit input thereof.
9. Method of generating a digital code indicative of liquid level
within a storage tank or the like upon receipt of a square wave
interrogation signal from a transmitter receiver of a tank gauging
system located at a central station remote from said storage tak
under survey but electrically connected to said transponder network
through an INTERROGATION, a MARK and a SPACE line of said tank
gauging system, comprising the steps of:
(A) encoding, as a updated, stored digital code, a series of input
signals representative of liquid level within said storage tank in
response to said interrogation signal;
(B) generating a microcircuit rest signal after said encoded
digital code has been generated and stored at a series of memory
addresses;
(C) generating in response to said reset pulse, sets of square wave
pulses of differing repetition rates and pulse widths;
(D) in response to selected sets of said square wave pulses of (C)
logically scanning said series of memory addresses and forming a
synthetic digital code at microcircuit signal levels directly
equivalent to said encoded digital code of (A); and
(E) as a function of said synthetic digital code, driving said MARK
and SPACE lines to generate a MARK-SPACE digital code at said
central station equivalent--in detail--to said encoded digital code
of (A) whereby said liquid level condition within said storage tank
can be indicated.
10. Method of claim 9 in which said each subsequent generated set
of square wave pulses of (C) is initiated in coincidence with a
trailing edge of an initially generated pulse of said succeeding
set of pulses, but all sets terinate in coincidence with
termination of said interrogation signal.
11. Method of claim 9 in which an initial first generated set of
square wave pulses of (C) is characterized by a repetition rate
higher than those of subsequent sets of square wave pulses for
scanninng--in sequence--said memory address contaning said encoded
digital code of (A) from which said synthetic digital code at
microcircuit signal levels can be generated.
12. Method of claim 11 in which each of said memory addresses is
designated address 1, address 2, address 3 . . . or address N.
13. Method of claim 12 with the additional substep of (C) being
lastly generated a N+1 address pulse terminating all operations.
.Iadd. 14. Transducer system for generating a digital code
indicative of liquid level within a storage tank or the like, upon
receipt of a square wave interrogation signal from a
transmitter/receiver of a tank gauging system located at a central
station remote from said storage tank but electrically connected to
said transducer system through an INTERROGATION, a MARK and a SPACE
line of said tank gauging system comprising:
(A) means for providing a series of input signals representative of
liquid level within said tank, said means being in circuit with a
series of look-up read-only-memories (ROM's);
(B) I/O network for receiving said interrogation signal and
connected to (A) for generating a reset signal therefrom in
response to said interrogation signal;
(C) an oscillator/ripple counter formed essentially of MSI's
connected to (A) and including at an input a network for receiving
said reset pulse from (A), said oscillator/ripple counter
generating, in response to said reset pulse, sets of square wave
pulses of differing repetition rates and pulse widths;
(D) a multiplexer and multi-segment decoder/driver means connected
to each other and to (B) responding to selected sets of said square
wave pulses to generate a synthetic digital code indicative of
liquid level at microcircuit signal levels at an output means of
said decoder/driver means;
(E) isolator/driver means having one or more inputs connected to
said decoder/driver means of (D), and one or more output means
connected to said MARK and SPACE lines controllable as a function
of said synthetic digital code to drive said MARK and SPACE lines
between tank gauging operating potentials for generating said
digital code of interest at said central station whereby said
liquid level condition within said storage tank can be indicated.
.Iaddend. .Iadd. 15. The transducer system of claim 14 in which an
initial first generated set of square wave pulses by (C) is
characterized by a repetition rate higher than those of subsequent
sets of square wave pulses, for enabling an input of said
multi-segment decoder/driver means of (D) at said same repetition
rate, and generating said synthetic digital code at microcircuit
signal levels. .Iaddend..Iadd. 16. Transducer systems of claim 15
in which said enabled input of said decoder/driver means of (D) is
the BLANK-ing input of a 7-segment decoder/driver. .Iaddend..Iadd.
17. The transducer system of claim 15 in which each subsequent set
of generated sets of square wave pulses provide in combination a
series of address commands at input means of said decoder/driver
means of (D) whereby X-in-16 particular address command per
interrogation cycle enables said decoder/driver means in circuit
with said MARK line through said switching transistor means, and
Y-in-16 address commands per cycle enable said SPACE line where X
and Y are whole numbers and X+Y=16, and whereby said synthetic code
indicative of liquid level is generated. .Iaddend..Iadd. 18.
Transponder system of claim 17 in which said input means of said
decoder/driver means of (D) is the 2.sup.0 bit input of a 7-segment
decoder/driver. .Iaddend..Iadd. 19. The transponder network of
claim 17 in which each subsequent set of generated sets of square
wave pulses provide in combination a series of multi-bit address
commands for said multiplexer means of (D) whereby output lines
thereof are placed in alternate circuit with said ROM's to receive
said synthetic code of interest. .Iaddend..Iadd. 20. Transponder
system of claim 19 in which said logic output lines connect to a
2.sup.0 bit data input of a 7-segment decoder/driver.
.Iaddend..Iadd. 21. Transponder system of claim 20 in which 2.sup.1
and 2.sup.2 bit inputs of said 7-segment decoder/driver are
continuously HI, and the 2.sup.3 bit input is continuously LOW
whereby first and second outputs of said 7-segment decoder/driver
oscillates between binary equivalents of an imaginary LED display
of the number "6" or "7", depending on HI, LOW state of said
2.sup.0 bit input thereof. .Iaddend.
Description
.Iadd.This application is a reissue of Ser. No. 854,917 filed Nov.
25, 1977, Pat. No. 4,194,177 issued Mar. 18, 1980. .Iaddend.
DISCLAIMER
While the above Abstract has been carefully written, the purpose of
such statements is to provide a non-legal description of the
contents of the application as a searching, scanning and
classification aid for technical persons. Accordingly, all
hereinbefore-presented statements are not intended to be used in
understanding or otherwise comprehending the principles of the
invention to be discribed in detail hereinafter, and are not, more
particularly, to be used in interpreting or in any way limiting the
scope and fair interpretation of the claims appended hereto.
RELATED APPLICATIONS
Related applications assigned to the assignee of the instant
application and incorporated herein by reference, all having a
common filing date, include: U.S. Ser. No. 855,033, J. S. Adamson
for "Transponder System Including an Oscillator Ripple Counter
Controlling A Coded Analog Multiplex Network In A Circuit With a
Driver/Gate Circuit For Generating "Red-Alert" End Condition
Digital Signals In A Storage Tank Gauging System"; U.S. Ser. No.
855,032, J. S. Adamson for "Transponder System Including An
Oscillator/Ripple Counter Controlling A Fixed Gray Code Logic
Network In Circuit With A Driver/Gate Circuit For Generating
"Red-Alert" End Condition Digital Signals In A Storage Tank Gauging
System"; and U.S. Ser. No. 854,916, J. S. Adamson for "Transponder
System Including An Oscillator/Ripple Counter Controlling A Fixed
Gray Code Logic Network In Circuit With A Decoder/Driver Network
For Generating "Red-Alert" End Condition Digital Signals In A
Storage Tank Gauging System".
FIELD OF THE INVENTION
This invention relates to transducers for monitoring fluid levels,
and more particularly, to a continuously operating fluid level
tranducer system formed essentially of MSI's (Medium Scale
Integrated Chips) in which a differential pressure (dp) cell in the
circuit with a digital encoding network through a DVM (Digital Volt
Meter) continuously produces an electrical signal proportional to
fluid level within a storage tank or vessel. The digital encoding
network is initiated by a MARK-SPACE interrogation signal of a
MARK-SPACE digital tank gauging system. The output of the digital
encoding network is a Gray code digital translation of the
electrical signals from the DVM which indicates fluid level within
the storage vessel and the like being monitored. The invention has
particular utility in monitoring tank farm networks associated with
an oil refinery and/or a chemical complex.
BACKGROUND OF THE INVENTION
In MARK-SPACE digital tank gauging systems for monitoring liquid
level, conductor buses directly connect all tank stations with a
central control monitoring location. Individual tank stations are
in multiplexed circuit connection with the central monitoring
location. During operations, line voltage of the conductor buses
must be held at rather high levels, say 48 volts, to avoid
accidental tripping of the system by natural phenomenon, such as
lighting. In order to create a MARK or SPACE on the lines of
interest, the transducer system associated therewith must generate
a complementary high level signal. However, experience has shown
that to generate such signals by solid state circuitry say
essentially MSI's (Medium Scale Integrated Chips) where such
circuits must be formed with minimum device count, simple control
capability and low power requirements, is exceedingly difficult to
accomplish. This is especially true if the circuit must also be
interfaced with present on-site tank gauging systems.
Moreover, there is a present need for an accurate transducer system
for monitoring fluid levels within oil refineries and/or chemical
complexes, such need having been brought about, to a large extent,
by changes in Federal and State laws. While normal refinery
practice seeks to avoid overloading storage tanks, now penalties
provided by Federal and State laws are so severe, that highly
accurate monitoring systems are mandatory. However, experience
shows that such systems are difficult to achieve because the
reasons previously mentioned, especially if a separate
analog-to-BCD-to-Gray code convertors, are to be used.
SUMMARY OF THE INVENTION
Liquid levels in a storage tank network are continuously monitored
by a highly reliable transducer system of the present invention
including a differential pressure (dp) cell in circuit with a
digital encoding network through a differential volt meter (DVM).
In operation and as a function of the dp cell output level, the DVM
is continuously applying binary-coded-decimal (BCD) signals to a
series of look-up ROM's (Read Only Memories) proportional to liquid
level within the storage tank being monitored. The ROM's retain,
in-memory, the Gray code translation of the BCD inputs. The ROM's
are then periodically accessed (based on a received MARK-SPACE
signal), via an analog multiplexer controlled by an
oscillator/ripple counter, to provide corresponding microcircuit
signals at the output of a 7-segment decoder/driver. These
microcircuit level signals are regenerated--levels compatible with
conventional tank gauging systems--using an isolator/driver network
in circuit with the 7-segment decoder/driver. The isolator/driver
network includes switching transistors, conduction of which, bring
MARK or SPACE lines tied thereto, down to ground potential and
create a pulse code proportional to liquid level for display at the
central station. Initially, the interrogation signal of the tank
gauging system is fed through a surge and polarity circuit to a
voltage divider network connected through a transformer to the DVM.
The DVM, in turn, resets the oscillator/ripple counter and starts
the oscillator clock to initiate operations. The dp cell is also
coupled to the DVM, and comprises a pair of flexible diaphragms
usually welded to opposite sides of a rigid steel disk. Mode of
operation: a force balance principal is used involving movement of
the diaphragms as a function of pressure in the diaphragm-disk
region, all elements cooperating to provide a drive current
proportional to pressure level at the DMV. Within the DVM,
analog-to-digital conversion of the output of the dp cell occurs.
The resulting BCD signals of the DVM are, in turn, applied to the
ROM's which hold a Gray code translation of the BCD signal in their
memory. The ROM's are periodically accessed via the analog
multiplexer controlled by the oscillator/ripple counter to provide
corresponding microcircuit level signals at the output of the
7-segment decoder/driver, as previously indicated. As the
oscillator/counter ripples through a cycle, its output stages are
sequentially enabled as follows: the least significant bit
(2.degree. bit) enables the BLANK-input of the 7-segment
decoder/driver at the highest repetition rate of the counter
whereby the Gray code in memory within the look-up ROM's (addressed
as a function of the occurrence of intermediate bits (2.sup.1,
2.sup.2 . . . 2.sup.N bits) from the counter), can be accessed in
sequence from the decoder. The resulting Gray code is, of course,
at microcircuit signal levels and to regenerate them at levels
compatible with conventional tank gauging systems requires the use
of the isolation/driver network in circuit between the 7-segment
decoder/driver and the MARK-SPACE lines of the tank gauging system,
as previously mentioned. The single cycle operation ceases because
the most significant bit, i.e., the 2.sup.N+1 bit of the
oscillator/counter, is fed back to a RC circuit at the input of the
latter which drives a diode in circuit therewith into conduction
which jams the oscillator clock.
Of some importance in operations is the isolation of the MARK-SPACE
tank gauging system from the transducer system of the present
invention through use of magnetic- and light-coupled isolation
networks.
DESCRIPTION OF THE DRAWINGS
Further features of the invention will become more apparent upon
consideration of the following detailed descriptions of the
invention when taken in conjunction with the accompanying drawings,
wherein:
FIG. 1 is a schematic of a tank gauging system servicing--from a
central monitoring location--a plurality of field stations, A,B . .
. M;
FIG. 2 is a schematic diagram illustrating in some detail a
transducer system in the present invention linked--electricaly--to
the tank gauging system of FIG. 1;
FIG. 3 is yet another schematic diagram illustrating in still more
detail the transducer system of FIG. 2;
FIGS. 4 and 5 are circuit diagrams of selected circuit elements of
the transducer system of FIG. 3; and
FIGS. 6a-f are timing charts of sets of square wave pulses
generated by the circuit of FIG. 3.
EMBODIMENTS OF THE INVENTION
Reference should now be had to FIG. 1 illustrating digital tank
gauging system 10 modified in accordance with the present
invention.
As shown, system 10 includes a transmitter-receiver 11 and
multiplexer 12 located at a central station 9. Receiver-transmitter
11 and multiplexer 12 are in circuit with each other and, in
addition with a plurality of field transmitter-receiver networks
13. The latter are located at, i.e., positioned within, a series of
tank monitoring stations A,B . . . M and connect to the former
through a series of MARK-SPACE conductor buses 14.
Each field transmitter-receiver network 13 at each of the different
monitoring station, A,B . . . M, is individually interrogated in
sequence by the receiver-transmitter 11 and multiplexer 12
operating at the central station 9. In more detail, the
transmitter-receiver 11 and multiplexer 12 interrogate each
individual station, A,B . . . M through the emission of a
predetermined MARK-SPACE interrogation signal. The last-mentioned
signal is usually designed to have a high relative amplitude, say
48 volts d.c., to avoid accidental tripping of the system. It is
also uniquely codable vis-a-vis station A,B . . . or M. In response
to such signal, a MARK or SPACE bit code, in turn, is generated by
the appropriate network 13 proportional to liquid level. Its
duration and polarity differs, however, than that of the
interrogation signal in that it must pull down the MARK or SPACE
line to ground potential and its pulse width is much smaller than
that of the interrogation pulse. To generate such signals using
MSI's (Medium Scale-Integrated Chips) within each network 13 has
been found to be exceedingly difficult in practice to
accomplish.
FIG. 2 shows a field transmitter-receiver network 13 in more
detail.
As shown, network 13 includes a continuous follower transducer
network (TN) 15 in circuit with pressure-sensitive sensor 17 within
storage tank 19. All control and data signals enter and leave TN
circuit 15 via elements of the conductor buses 14 previously
mentioned to separately control and interact with condition sensor
17.
In operation, the sensor 17 provides pressure signals proportional
to liquid level within the tank 19. Such signals are fed, in turn,
to TN circuit 15 where it is used to produce, ultimately, a Gray
code translation of the liquid level within the tank 19 for display
at the central station 9.
FIG. 3 illustrates transducer system 15 in more detail.
As shown, system 15 includes a differential pressure (dp) cell 18
in circuit with a digital encoding network 20 through a digital
volt meter (DVM) 21. Briefly, the cell 18 first accepts the
pressure signals from the sensor 17 within the storage tank 19 of
FIG. 2 then converts these signals to analog electrical values. The
analog electrical signals are then presented to DVM 21.
The cell 18 is conventional in the art and briefly, can comprise a
pair of flexible diaphragms welded to opposite sides of a rigid
steel disk. Its mode of operation: a force balance principal is
utilized involving movement of the diaphragms as a function of the
differential pressure signals proportional to liquid level within
the storage tank. The diaphragm and disk combine, in function, to
provide an electrical drive current proportional to the
differential pressure signals, and hence, also to liquid levels.
The resulting analog electrical signals are used to drive DVM
21.
When enabled by a MARK-SPACE interrogation signal, DVM 21 initiates
both external and internal operations of the system.
Externally, the DVM 21 provides a power-on reset pulse via enable
bus 23 for oscillator/ripple counter 24 of digital encoding network
20 of the present invention. As a result, output stages 24B-24E of
the oscillator/counter 24 are reset to zero and a clock (not shown)
therein which paces all operations within the system, is
started.
Internally, the DVM 21 performs analog-to-digital conversion of the
updated analog data from the dp cell 18 and presents the resulting
binary-coded-decimal data (BCD) to a series of look-up Read-Only
Memories (ROM's) 25. The ROM's 25 retain, in memory, the Gray code
translation of the BCD input. The ROM's 25 are accessed via
multiplexer 26 under control of oscillator/ripple counter 14, the
data from the ROM's 25 being accessed to 7-segment decoder/driver
27 and thence through isolater/driver network 28 and I/O 29 back to
the central station for display.
Cyclic operations of the oscillator/counter 24, ROM's 25,
multiplexer 26 and 7-segment decoder/driver 27 is summarized and
set forth in detail in Table I. Note that the ultimate code
transmitted is dependent on the particular BCD input to the ROM's
25. Also note that DMV 21 is of conventional design. In this
regard, a Weston model 1234 described somewhat in U.S. Pat. No.
3,051,939, has been found to be adequate in this regard.
TABLE I ______________________________________ Disable Data Enable
2.sup.N+1 Bit 2.sup.N . . . 2.sup.2,2.sup.1 Bits 2.sup.0 Bit
Comment ______________________________________ 0 0000 0 Reset &
start at Address 0 of multiplexer 26 0 0000 1 Enable Address 0: a
SPACE is generated 0 0001 0 Set to Address 1 0 0001 1 Enable
Address 1 0 0010 0 Set Address 2 0 0010 1 Enable at Address 2 0
0011 0 Set to Address 3 0 0011 1 Enable at Address 3 0 0100 0 Set
to Address 4 0 0100 1 Enable at Address 4 0 0101 0 Set to Address 5
0 0101 1 Enable at Address 5 0 0110 0 Set to Address 6 0 0110 1
Enable at Address 6 0 0111 0 Set to Address 7 0 0111 1 Enable at
Address 7 0 1000 0 Set to Address 8 0 1000 1 Enable at Address 8 0
1001 0 Set to Address 9 0 1001 1 Enable at Address 9 0 1010 0 Set
to Address 10 0 1010 1 Enable at Address 10 0 1011 0 Set to Address
11 0 1011 1 Enable at Address 11 0 1100 0 Set to Address 12 1100 1
Enable at Address 12 1101 0 Set to Address 13 0 1101 1 Enable at
Address 13 0 1110 0 Set to Address 14 0 1110 1 Enable at Address 14
0 1111 0 Set to Address 15 0 1111 1 Enable at Address 15 1 0000 0
Clock jammed; operation cease
______________________________________
Briefly, in operation, the interrogation voltage pulse is divided
and the divided pulse is used to provide (via DVM 21 and enable bus
23) a reset pulse for oscillator/counter 24. In addition to
resetting all output stages 24B-24E of the oscillator/counter 24 to
zero, the oscillator clock is also commenced to initiate system
operations. As a result, a series of sequential binary "addresses"
are generated by the counter 24 which enable, in sequence, the
series of ROM's 25 through analog multiplexer 26. The data
(HI,LOW's)--at microcircuit input levels--enable through the
multiplexer 26 to the 7-segment decoder/driver 27. The fact that
the resulting code of interest from the decoder 27 is at
microcircuit signal levels, has been previously mentioned, and the
former must be increased to a level which is compatible with
conventional tank gauging systems. To generate a compatible code,
each microcircuit pulse (either a SPACE or MARK) controls switching
transistors within isolation/driver network 28 connected to SPACE
or the MARK lines 14B or 14A of the conventional tank gauging
system attached to I/O 29 to bring the latter down--momentarily--to
ground potential. Result: the liquid level digital data can be
transmitted back to the central station through the I/O 29 for
display and analysis.
Having brifly described operations, above, a more detailed analysis
of I/O 29 is in order and is presented below with reference to FIG.
4.
As shown in FIG. 4, I/O 29 includes a surge and polarity limiting
circuit 30 at its input. The circuit 30 comprises a reverse
polarity protection diode 31. A relay coil 32 is in circuit with
the diode 31 through surge limiting resistor 33. In operation, the
diode 31 only conducts when an interrogation signal of the correct
polarity as applied to the I/O 29. Note that the interrogation
signal energizes the relay coil 32 (closing relay contacts 34A-34C
through 34D). Voltage divider 35 is common in the art and reduces
the voltage of the interrogation pulse via resistor 33 and Zener
diode 37 to a level compatible with microcircuit logic, e.g., say
at about 12 volts in the instant application, for use within DVM 21
through power-on reset/isolation network 36 in circuit therewith.
With the closing of relay contacts 34B and 34C, note the
isolator/driver network 28 is placed in circuit with outside data
MARK and SPACE bus lines 14A and 14B, respectively.
Power-on-reset generation can be further explained with reference
to the reset-isolation network 36 of FIG. 4.
Reset/isolation circuit 36 includes a pulse forming network 38 in
circuit with transformer 39. Briefly, in operation the former
generates a reset pulse from the interrogation pulse while the
latter isolates the digital encoding network 20 including DVM 21
from the MARK-SPACE system itself.
In more detail, the network 38 includes silicon-controlled
rectifier 41 in circuit with a capacitor 42, Zener diode 43 and
resistor 44. After the interrogation pulse occurs, rectifier 41 and
Zenor diode 43 are enabled, thereafter, causing capacitor 42 to
discharge through primary windings 45 of the transformer 39 and
generating at secondary windings 46, a reset pulse for DVM 21 in
circuit with dp cell 18. Since between the windings 45 and 46
electrical isolation is complete, the effect of different ground
potentials are minimized between the MARK-SPACE tank gauging system
and DVM 21.
Returning to FIG. 3, recall that data at ROM's 25 is received from
DVM 21 as a function of multiple analog signals from dp cell 18.
Hence, each ROM 25 has digital significance dependent on its
relative position in the data flow. In operation, the data flow is
controlled (GAtED) via BLANK-ing input 50 at 7-segment
decoder/driver 27 which receives, on an iterative basis, the
2.degree. bit input from oscillator/counter 24.
FIG. 5 illustrates data flow within decoder/driver 27 in
conjunction with isolator/driver 28, in more detail.
Other inputs of decoder/driver 27 of interest of the present
invention includes the 2.sup.1 bit and 2.sup.2 bit inputs 51,52
connect to a separate power bus 49; the 2.sup.3 bit input 53 and
the data input 54 connected to ROM's 25 connects to ground. As a
result, inputs 51 and 52, i.e., the 2.sup.1, 2.sup.2 bit inputs of
the 7-segment decoder, are continuously enabled (HI's) while input
53, i.e., the 2.sup.3 bit input, is a LOW during all operations of
the decoder. Outputs 55 and 56 of the decoder/driver connect to
switching transistors 70,71, respectively, of isolation/driver 28
as explained below. As address bit codes (HI's and LOW's) from the
ROM's 25 materialize at input 54 of decoder 27, the total operation
becomes akin to a 16-addressable ROM. That is to say, the 2.sup.1
and 2.sup.2 bit inputs to the decoder are always enabled while the
2.sup.3 input is LOW so that the decoder oscillates between the
binary equivalents of an imaginary LED display of the number "6"
and "7" at its outputs 56 or 55, depending on the bit state at
input 54, this condition, of course, being synchronized by proper
gate bits (HI's) at input 50. E.g., if the input 54 is HI, a
"seven" is generated at output 55; while if it is LOW, a "six" is
generated at output 56. At the above outputs, the resulting drive
currents of the decoder is associative, with two non-overlapping
segments of the normal 7-segment LED display being summable (with
generation of the number "7") to cause the MARK line transistor 70
to conduct and pull the MARK line 14A down to ground potential,
while drive currents associated with two other non-overlapping
segments (for generation of the number "six") cause the SPACE line
transistor 71 to conduct and pull, likewise, the SPACE line 14B
down to ground potential.
Table II below indicates the nature of the 2-in-7 drive current
generation by decoder/driver 27.
TABLE II ______________________________________ Total Segments
Segments Used Segments Used Available To Drive To Drive 7-Segment
LED To Be MARK SPACE Configuration Driven Transistor 70 Transistor
71 ______________________________________ ##STR1## 7, i.e., 2,
i.e., 2, i.e., ##STR2## a, b, c, d, e, f and g a, b e f ##STR3##
##STR4## ##STR5## ______________________________________
In a usual LED display of the number "6" (normally occurring with a
LOW at input 54, and HI's at inputs 51,52) the following segments
would be enabled: f, e, d, c and g. And for display of the number
"7" (occurring normally with HI's at inputs 54,51 and 52) the
following segments would be enabled: a, b, c. Hence,
non-overlapping segments are a,b (when the number "7" is generated)
and e, f, d, g, (when the number "6" is generated). In order to
equalize current outputs from the non-overlapping segments, only
segments d,e were placed in circuit with SPACE transistor 71,
however.
But switching transistors 70,71 are not directly connected to
outputs 55,56 but use light-coupled interconnection via LED's
(light enabling diodes) 73, 74, 75 and 76 in circuit with switching
transistors 70,71 through light sensitive transistors 77 and 78.
I.e to say, at outputs 55,56 the decoder is further modified so
that the resulting drive currents from the decoder are
light-coupled via LED's 73-76 through light-sensitive transistors
77 and 78 to switching transistors 70,71.
Note that the signal level at light-sensitive transistors 77,78 is
at microcircuit levels but that switching transistors 70,71 provide
sufficient drive levels to bring down MARK and SPACE lines 14A to
ground potential.
Return to FIG. 3 to review the operational aspects of the
transponder system 16 of the present invention.
Note initially the effect of reset pulse of the DVM 21 on
operations of the oscillator/ripple counter 24. Not only are all
output stages of the counter set to zero by such pulse, but also
the latter initiates operation of the oscillator clock. As the
counter 24 ripples through a single cycle, individual output stages
are activated the controllably enable 7-segment decoder/driver 27
and Iso-driver 28. The result: Gray-code translations (within ROM's
25) of the BCD data from DVM 21 are fed back via I/O 29 to the
central station for display and analysis.
E.g., the least significant bit, say the 2.degree. bit of the
oscillator/counter 24, can be utilized to selectively enable
BLANK-ing input 50 of the decoder/driver 27 while intermediate bits
2.sup.1, 2.sup.2 . . . 2.sup.N bits connect to input 54 of the same
decoder. These intermediate bits, i.e., the 2.sup.1, 2.sup.2 . . .
2.sup.N bit code at input 54 are in sequential binary combinations
which enable--also in sequence--address inputs of the multiplexer
26 to the ROM's 25. As a result, the state (HI or LOW's) of the
ROM's 25 are sampled, and the Gray code equivalent of the analog
liquid level data from the dp cell is provided at the 7-segment
decoder/driver 27. Thereafter, the SPACE-MARK lines are modulated
akin to a 16.times.1 ROM in which a X-in-16 particular address
enables the MARK line while Y-in-16 address enable the SPACE line
to provide Gray code translation of the liquid level of
interest.
The most significant bit of the oscillator counter 24 say the 2 N+1
is last fed via bus 24F back to the diode 75 at the input to the
oscillator/counter 24 (i.e., to RC circuit 76). In operation,
conduction of the diode 75 "jams" the oscillator clock of the
latter. All output stages of the counter are then placed in an
inhibited state. All operations cease.
The synthetic Gray code generation can be further explained with
reference to the timing chart of FIG. 6.
As shown, the pulse width of interrogation signal 80 of FIG. 6A is
such that usually a certain total of MARK and SPACE pulses, say
sixteen, can be provided per interrogation cycle. Hence, the number
and pulse width of the enable (2.degree. bit) pulses of the pulse
code 81 of FIG. 6B for the multiplexer 26 would correspond in kind
to the MARK and SPACE pulses ultimately generated and displayed.
I.e., the square wave enabling (2.degree.) code 81 would have a
repetition rate and pulse width matchable in kind to the MARK and
SPACE pulses generated by the switching transistors 70,71. This is
not true for the address command codes 82, 83, 84 and 85, of FIGS.
6C-6F. Each is initiated by the falling edge of the initial pulse
of the preceeding set of square wave address pulses and has a
progressively increasing pulse width and correspondingly a
progressively decreasing repetition rate. Note all codes 81-85 as
well as the disabling bit terminate with the trailing edge of the
interrogation pulse 80 of FIG. 6A.
From the above, it is apparent that the invention as hereinbefore
described has variations readily apparent to those skilled in the
art and hence the invention is not limited to the combination of
embodiments hereinbefore described but should be given the broadest
possible interpretation in the terms of the following claims.
* * * * *