U.S. patent number 3,641,536 [Application Number 05/028,379] was granted by the patent office on 1972-02-08 for gasoline pump multiplexer system for remote indicators for self-service gasoline pumps.
This patent grant is currently assigned to Veeder Industries Inc.. Invention is credited to Frank B. Prosprich.
United States Patent |
3,641,536 |
Prosprich |
February 8, 1972 |
GASOLINE PUMP MULTIPLEXER SYSTEM FOR REMOTE INDICATORS FOR
SELF-SERVICE GASOLINE PUMPS
Abstract
A multiplexer system employing a form of pulse width modulation
and detection. The system is particularly adapted to use in a
telemetering system for remote indicators. The system operates in
connection with a self-service gasoline pump and transmits via a 60
Hz. powerline gallons and dollars information. A modified form of
the system transmits only dollars or only gallons information for a
plurality of pumps. The system can be further adapted for inventory
control purposes. Variants include signal forcing and totalizing
circuits for a plurality of independent information sources
providing absolute accuracy.
Inventors: |
Prosprich; Frank B. (West
Hartford, CT) |
Assignee: |
Veeder Industries Inc.
(Hartford, CT)
|
Family
ID: |
21843125 |
Appl.
No.: |
05/028,379 |
Filed: |
April 14, 1970 |
Current U.S.
Class: |
340/870.15;
222/23; 340/870.18; 340/870.19; 340/870.24; 377/21; 340/538.12;
340/538.11 |
Current CPC
Class: |
B67D
7/228 (20130101) |
Current International
Class: |
B67D
5/22 (20060101); G08c 019/16 () |
Field of
Search: |
;340/203,206,310,182,184
;222/26,23,76 ;235/92FL,92AC,151.34 ;73/194E |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Mooney; Robert J.
Claims
I claim:
1. In a dispensing system having at least one dispensing apparatus
which is capable of generating separate triggering pulses
corresponding to fractional parts of at least two different units
of measurement related to the dispensed product, a multiplexer
system comprising:
a pulse width modulator responsive to one of said triggering pulses
for generating a series of pulses having a first duration separated
by intervals having a second duration, said pulse width modulator
also being responsive to another of said triggering pulses for
generating a series of pulses having said second duration separated
by intervals having said first duration, and said pulse width
modulator further being responsive to the simultaneous occurrence
of the two triggering pulses for generating a series of pulses
having said first duration separated by intervals having said first
duration,
a gated carrier frequency oscillator connected to said pulse width
modulator and providing a pulse modulated output,
transmission means receiving said pulse modulated output from said
gated carrier frequency oscillator for transmitting the modulated
signal to a central point,
receiver means at said central point for receiving the transmitted
signal and providing a detected output,
pulse sorter means connected to receive the detected output from
said receiver for providing a first output in response to a series
of pulses having said first duration and a second output in
response to a series of pulses separated by intervals having said
first duration, and
indicator means connected to each of said first and second outputs
of said pulse sorter means for providing an indication at the
central point whenever either of said triggering pulses occur.
2. A multiplexer system as recited in claim 1 wherein said pulse
width modulator comprises:
an astable multivibrator, and
switching means responsive to said triggering pulses for
selectively changing the time constants of said astable
multivibrator.
3. A multiplexer system as recited in claim 2 wherein said astable
multivibrator includes a plurality of timing resistors and said
switching means further comprises:
a first one-shot triggered by one of said triggering pulses for
producing a pulse output having a fixed duration substantially
longer than both said first and second durations,
a second one-shot triggered by another of said triggering pulses
for producing an output pulse having a duration equal to that of
the output of said first one-shot,
a first electronic switch connected to the output of said first
one-shot and operable to connect a first combination of said timing
resistances to said astable multivibrator,
a second electronic switch connected to said second one-shot and
operable to connect a second combination of timing resistances to
said astable multivibrator,
an AND gate receiving as its inputs the outputs of both said first
and said second one-shots and providing an output only when the
outputs from said first and second one-shots are coincident,
and
a third electronic switch connected to said AND gate and operable
to connect a third combination of timing resistances to said
astable multivibrator.
4. A multiplexer system as recited in claim 1 wherein said pulse
sorter means comprises:
first and second pulse width discriminators each operable to detect
a pulse having said first duration, one of said pulse width
discriminators receiving the detected output from said receiver
means and the other of said pulse width discriminators receiving
the inversion of the detected output from said receiver means,
and
first and second integrating one-shots connected to the output of
said first and second pulse width discriminators, respectively.
5. A multiplexer system as recited in claim 1 wherein said
dispensing apparatus is a gasoline pump and said units of
measurement are dollars and gallons, respectively, and said
indicator means provides numerical readouts of the number of
gallons dispensed and the dollar value thereof.
6. A multiplexer system comprising
a pulse width modulator responsive to a first data pulse for
generating a series of pulses having a first duration separated by
intervals having a second duration, said pulse width modulator also
being responsive to a second data pulse for generating a series of
pulses having said second duration separated by intervals having
said first duration, and said pulse width modulator further being
responsive to the simultaneous occurrence of said first and second
data pulses for generating a series of pulses having said first
duration separated by intervals having said first duration,
a gated carrier frequency oscillator connected to said pulse width
modulator and providing a pulse modulated output,
transmission means receiving said pulse modulated output for
transmitting the modulated signal to a remote point,
receiver means at said remote point for receiving the transmitted
signal and providing a detected output,
pulse sorter means connected to receive the detected output from
said receiver for providing a first output in response to a series
of pulses having said first duration and a second output in
response to a series of pulses separated by intervals having said
first duration, and
indicator means connected to each of said first and second outputs
of said pulse sorter means for providing an indication at the
remote point whenever either of said first or second data pulses
occur.
7. A multiplexer as provided in claim 6 wherein said pulse width
modulator comprises:
an astable multivibrator, and
switching means responsive to said first and second data pulses for
selectively changing the time constants of said multivibrator.
8. A multiplexer system as recited in claim 7 wherein said astable
multivibrator includes a plurality of timing resistances and said
switching means comprises
a first one-shot responsive to said first data pulse for generating
an output pulse having a duration substantially longer than either
said first or second durations,
a second one-shot responsive to said second data pulse for
generating an output pulse equal to that generated by said first
one-shot,
a first electronic switch connected to said first one-shot and
operable to connect a first combination of said timing resistances
to said astable multivibrator,
a second electronic switch connected to said second one-shot and
operable to connect a second combination of said timing resistances
to said astable multivibrator,
an AND gate connected to both said first and said second one-shots
and producing an output when the outputs of said first and said
second one-shots are coincident, and
a third electronic switch connected to the output of said AND gate
and operable to connect a third combination of said timing
resistances to said astable multivibrator.
9. A multiplexer system as recited in claim 8 wherein said receiver
means comprises:
an input tank circuit resonant at the carrier frequency,
a logarithmic amplifier connected to said input tank circuit and
providing an amplified output which emphasizes smaller signal
amplitudes,
a tuned amplifier connected to the output of said logarithmic
amplifier, and
a threshold detector connected to said tuned amplifier providing an
output substantially identical to the modulation envelope.
10. A multiplexer system as recited in claim 9 wherein said pulse
sorter means comprises:
first and second pulse width discriminators each operable to detect
pulses having said first duration, one of said pulse width
discriminators being connected to receive the output of said
threshold detector and the other of said pulse width discriminators
being connected to receive the inversion of the output of said
threshold detector, and
first and second integrating one-shots connected to respective ones
of the outputs of said pulse width discriminators for providing
output pulses having durations equal to the duration of the outputs
of said first and second one-shots.
11. In a self-service gasoline dispensing system having a plurality
of gasoline pumps each of which are capable of generating trigger
pulses corresponding to fractional parts of units of measurement
related to the dispensed gasoline, a remote indicator system
comprising
a sender for each pump responsive to the trigger pulses produced
thereby and producing a modulated signal characteristic of its
particular pump, each of said senders being connected to a common
powerline,
a receiver for each sender located at a central station and also
coupled to said common powerline, each of said receivers being
responsive to the characteristic modulated signal produced by its
corresponding sender, and output means connected to each receiver
for producing an indication of the amount of gasoline dispensed,
said output means comprising:
a plurality of one-bit memories, each of said memories being
connected to a respective receiver corresponding to one of said
plurality of gasoline pumps,
strobing means for strobing the outputs of each memory at least
twice between two consecutive trigger pulses generated by its
related pump, and
accumulating means connected to said strobing means for totalizing
the total number of trigger pulses generated by all of said
plurality of gasoline pumps.
12. A remote indicator system as recited in claim 11, wherein said
strobing means comprises:
a plurality of AND gates each connected to a respective one of said
plurality of one-bit memories,
a clock oscillator, and
a counter connected to said clock oscillator and operative to
strobe each AND gate in succession.
13. A remote indicator system as recited in claim 12 wherein said
accumulating means comprises:
a flip-flop connected to be toggled back and forth by the combined
outputs of said AND gates and the output of said clock
oscillator,
a stepping motor driven by the outputs of said flip-flop, and
a totalizing counter driven by said stepping motor.
14. A remote indicator system as recited in claim 11 wherein said
strobing means comprises:
a plurality of AND gates each associated with a respective one of
said plurality of one-bit memories,
said AND gates each having three inputs, the first of said inputs
connected to receive a signal from its associated one-bit memory,
the second of said inputs connected to receive the input signal to
said one-bit memory, and the third of said inputs connected to said
strobing means
whereby an input signal to said one-bit memory prevents said AND
gates from passing a signal.
15. In a self-service gasoline dispensing system having a plurality
of gasoline pumps each of which are capable of generating trigger
pulses corresponding to fractional parts of units of measurement
related to the dispensed gasoline, a remote indicator system
comprising
a sender for each pump responsive to the trigger pulses produced
thereby and producing a modulated signal characteristic of its
particular pump, each of said senders being connected to a common
powerline,
a receiver for each sender located at a central station and also
coupled to said common powerline, each of said receivers being
responsive to the characteristic modulated signal produced by its
corresponding sender, and output means connected to each receiver
for producing an indication of the amount of gasoline dispensed,
each sender being connected to the powerline by a coupling network
comprising:
a coupling transformer having primary and secondary windings, said
primary winding receiving the output of said sender,
a capacitor connected across said primary winding to form a tank
circuit resonant at the signal frequency,
at least one coupling capacitor connected in series with the
secondary winding of said coupling transformer and the powerline
for blocking the powerline frequency, and
at least one current forcing resistor connected in series between
said coupling capacitor and said secondary winding.
Description
SUMMARY OF THE INVENTION
The invention generally relates to multiplexer and telemetering
systems, and is of special significance to a remote control system
for one or more gasoline pumps at a filling station in which
signals reflecting the operation of each pump are conducted on the
60 Hz. powerline to a control point inside the station.
Most multiplexer systems in common use generally employ frequency
or amplitude modulation techniques or a combination of both. Where
the intelligence to be transmitted in the several channels is
fairly complex or broadband, these systems are highly suitable.
However, in those applications involving the most simple form of
information, i.e., on or off, frequency and amplitude modulation
techniques as applied to multiplexing become too complicated when
compared to the data to be transmitted. Furthermore, in the
transmission of elementary on-off data, reliability is of utmost
importance. Noise, therefore, becomes an increasingly important
factor inasmuch as noise-induced frequency and amplitude variations
on transmissions can cause serious error in an accumulated total at
the receiver. Pulse modulation techniques are uniquely suited to
the transmission of this type of information. Multiplexing of
simultaneously occurring pulse data usually requires some form of
elaborate buffer memory system in order to avoid losing bits of
data. As a result, this type of system becomes prohibitively
expensive for many applications.
A simple pulse multiplex data transmission system is particularly
useful in a self-service gasoline station wherein data pertaining
to each pump, such as dollar amount of sale and total gallons, is
supplied to a central pay booth which would require only one
attendant. In addition, such a system may provide a means of
automatic inventory control.
It is therefore an object of the present invention to provide a
simple pulse data multiplexer system.
It is another object of this invention to provide a multiplexer and
telemetering system for a dispensing system.
It is a further object of the instant invention to provide a
gasoline pump multiplexer system with remote indicators for a
self-service gasoline station.
It is yet another object of the invention to provide a multiplexer
system for a dispensing system which incorporates an inventory
control.
Other objects will be in part obvious and in part pointed out more
in detail hereinafter.
A better understanding of the invention will be obtained from the
following detailed description and accompanying drawings which set
forth certain illustrative embodiments and are indicative of the
various ways in which the principles of the invention are
employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a pictorial illustration showing gasoline pumps in a
remote control service station;
FIG. 2 is a block and schematic diagram of a sender unit in the
multiplexing system according to the invention;
FIG. 3 is a block and schematic diagram of a receiver unit for the
multiplexing system according to the invention;
FIG. 4 is a timing diagram useful in understanding the operation of
the circuits shown in FIGS. 3 and 4;
FIGS. 5A and 5B are simplified schematic diagrams which illustrate
a scheme for obtaining a stable signal at the receiver over a
powerline regardless of load variations and noise on the
powerline;
FIGS. 6A and 6B are block diagrams illustrating modifications of
the system according to the invention which are useful in
transmitting price only information or in inventory control;
FIG. 7 is a logic diagram illustrating the circuitry of the
parallel to serial converter and one-bit memories in FIGS. 6A and
6B; and
FIG. 8 is a timing diagram useful in understanding the operation of
the logic shown in FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Briefly stated, the present invention provides a simple pulse
multiplexing system which generates two different pulses which
represent, for example, gallons and dollars. Pulsers representing
fractions of a dollar and fractions of a gallon of gasoline provide
inputs to a modulator which includes one-shot multivibrators that
act to switch different timing resistors into the modulator. Each
one-shot switches a switch to gate a burst of carrier frequency of
a fixed duration such as 20 ms. The dollar pulser provides a pulse
for each cent and operates through the modulator to cause the
switch to produce a burst of spaced pulses which are ON 1.9 ms.
throughout the 20 ms. burst. The gallons pulser operates on the OFF
cycle to provide a burst of spaced OFF pulses of 1.9 ms. for the 20
ms. interval. The pulses can overlap partially or entirely. This
results in a system which is neither frequency nor amplitude
sensitive but rather is sensitive to the pulse width of the ON or
OFF pulses. In a simplified version, the invention is useful in a
system which operates to telemeter price or gallons information
only. A modification of this system contemplates the telemetering
of gallons information from a plurality of pumps to a central
station where the information is totalized for purposes of
inventory control. Incorporated into this system is a parallel to
serial converter having simple one-bit memories to buffer the input
data from the several pumps.
Referring now to the drawings, wherein like reference numerals
refer to identical or similar structures throughout the several
views, FIG. 1 generally illustrates a self-service gasoline station
which employs the gasoline pump multiplexer system according to the
invention. Such a station typically comprises a plurality of
gasoline pumps 10 on each of the several service islands 11.
Typically, a customer 13, upon alighting from his vehicle 12,
removes the nozzle 15 from its support, turns the handle 14 to
reset the computer and proceeds to dispense gasoline into the tank
of his vehicle 12.
Data, such as gallons dispensed and price of sale, are transmitted
to a remote station 16, which may be conveniently located at the
exit ramp of the service station, and after filling the tank of his
vehicle 12, the customer replaces the nozzle 15 of pump 10 on its
support and proceeds to the station 16 where the attendant on duty
then looks at a display panel, collects the indicated amount in his
remote control panel corresponding with the pump used by the
customer.
For purposes of illustration only, the electronics of the
multiplexer system is shown as housed in a box 18 supported above
the service island 11 by a pole 19. The pole 19 serves as a conduit
for wires that connect the multiplexer system to the mechanism of
pump 10. Box 18 is shown as connected to the service station 16 by
the normal 60 Hz. powerlines 20 which supply power to the pump
motors of the pumps 10 and signals between the box 18 and the
service station 16 may be by way of carrier modulation superimposed
on the 60 Hz. powerline frequency although other forms of
transmission may be employed.
The basic multiplexer system of the invention employs a form of
pulse width modulation and detection in which the carrier is
switched on and off, effectively producing a resultant wave form
analogous to 100 percent square wave modulation. At a given carrier
frequency, by varying both ON and OFF times and employing ON time
and OFF time recognition circuitry at the receiving end, it is
possible to transmit two distinctive signals simultaneously. FIG. 2
of the drawings illustrates how this is done. This circuit is the
sender which is associated with a specific one of the gasoline
pumps 10. The circuit has two inputs, a gallons input and a dollars
input. These inputs are pulses which are generated by conventional
pulsers which are a part of the mechanism of the pump 10. Each
pulse at the gallons input would represent a fractional part of a
gallon, say one-tenth of a gallon, and each pulse at the dollars
input would represent a fractional part of a dollar, say one cent.
These pulse inputs trigger respective one-shots 21 and 22 which
produce output pulses having a fixed duration of, for example, 20
ms. The output of one-shot 21 is connected to one input of AND-gate
23 which in combination with NPN 24 forms an electronic switch. The
output of one-shot 21 is also connected to one input of AND-gate
25. In like manner, the output of one-shot 22 is connected to one
input of AND-gate 26 which in combination with NPN-transistor 27
forms another electronic switch. The output of one-shot 22 is also
connected to the second input of AND-gate 25. The output of
AND-gate 25 is connected to the second input of AND-gates 23, 26
and to the base of NPN-transistor 29 to provide a third electronic
switch.
Each of the three electronic switches just described are used to
control the period of a square wave generator 30 which is
preferably an astable multivibrator. Generator 30 comprises two
programmable unijunction transistors (PUTs) having their cathodes
connected in common to ground and their anodes connected by a
timing capacitor 33. The gate electrode of PUT 31 is connected to a
voltage divider comprising resistor 34 and resistor 35 connected in
series across a source of positive voltage and ground. Similarly,
the gate electrode of PUT 32 is connected to a voltage divider
comprising resistor 36 and resistors 37 and 38 connected in series
across the source of positive voltage and ground. A timing resistor
39 is connected between the anode of PUT 32 and the source of
positive voltage. A switchable timing resistance 40 is also
connected to the anode of PUT 32. Three switchable timing
resistances 41, 42 and 43 are connected to the anode of PUT 31.
Timing resistor 41 is connected to the emitter of transistor 24,
timing resistor 42 is connected to the emitter of transistor 29,
and timing resistors 40 and 43 are connected in common to the
emitter of transistor 37.
A pulse at the gallons input triggers one-shot 21. As shown at the
top of FIG. 4 of the drawings, this pulse enables AND-gate 23 which
causes transistor 24 to conduct. Transistor 24 is biased into
saturation effectively connecting timing resistor 41 to the source
of positive voltage. Under these conditions, the astable
multivibrator 30 begins to oscillate, producing a series of pulses
at the gate electrode of PUT 32 as represented by the modulation
envelope shown in FIG. 4. The value of timing resistor 41 is
selected such that the duration of the output pulses is relatively
short, say 0.7 ms., compared with the interval between pulses which
might be 1.9 ms. If, on the other hand, a pulse at the dollars
input triggers one-shot 22, AND-gate 26 and transistor 27 will
conduct with the result that timing resistors 40 and 43 are
effectively connected to the source of positive voltage. The values
of timing resistors 40 and 43 are chosen such that the pulse
pattern output at the gate of PUT 32 is just the opposite of that
produced by a pulse at the gallons input, that is the pulse would
be ON for 1.9 ms. and OFF for 0.7 ms. This is shown at the
right-hand part of the modulation envelope illustrated in FIG 4. It
is possible for the pulses produced by one-shot 21 and one-shot 22
to overlap. When this happens, the output of AND-gate 25 causes
transistor 29 to conduct and inhibits AND-gates 23 and 26. This in
turn causes timing resistor 42 to be effectively connected to the
source of positive voltage. The value of timing resistor 42 is
chosen such that a symmetrical pulse pattern output is produced at
the gate electrode of PUT 32. In other words, the output of astable
multivibrator 30 during this overlap period will be a series of
pulses 1.9 ms. in duration separated by intervals of 1.9 ms.
A Colpittis oscillator 44 with good temperature stability is used
to generate the carrier. The output of oscillator 44 is connected
to the base of PNP-transistor 45 which is connected as an emitter
follower. The output of emitter follower transistor 45 is connected
to the base of transistor 46 which acts as a gated buffer
amplifier.
Resistors 37 and 38 form a voltage divider which is connected to
the base of NPN-transistor 47 which in combination with
PNP-transistor 48 comprises an electronic switch. The collector of
transistor 48 is connected to the base of transistor 46, and when
transistor 48 conducts, transistor 46 is biased to nonconduction.
When transistor 48 is off, transistor 46 passes the output of
oscillator 44 to the input of power amplifier 49.
The power amplifier 49 provides sufficient line drive to overcome
the effects of powerline loading at the carrier frequency,
delivering approximately 100 milliwatts to the line through a line
coupling network 50. The coupling network 50 comprises a coupling
transformer 51 having primary and secondary windings. A capacitor
52 is connected across the primary of coupling transformer 51 to
form therewith a tank circuit resonant at the carrier frequency.
Relatively broad tuning is employed in the primary circuit, and
care is taken to ensure a clean undistorted carrier signal on the
line to avoid harmonic sideband problems. Small coupling capacitors
53 and 54 presenting a high impedance at the powerline frequency
are employed for isolation in series with the secondary of the
output transformer 51. Interposed between these coupling capacitors
and the secondary winding of transistor 51 is a resistance network
comprising a shunt resistance 55 and two series resistances 56 and
57. A neon indicator lamp 58 may be connected across the output to
the powerline.
The series resistances 56 and 57 may be described as current or
signal forcing resistances and have as their objective to ensure a
stable signal at the receiver over the powerline regardless of load
variations and noise on the powerline. FIG. 5A shows in simplified
schematic form the relationship of the current forcing resistance
56 to the circuitry of the system. The sender which is shown in
FIG. 2 may be considered analogous to a current generator 59.
Resistance 56 is placed in series with the current generator 59,
and a receiver 60 is connected to a current transformer 61 placed
across the powerlines in series with capacitor 62. Resistance 56
has a value chosen sufficiently high so that capacitor 62, which
serves as a high frequency short across the powerlines, produces a
substantially constant current output for an information signal
delivered to the receiver 60 regardless of variations in the line
loading and noise. Also shown in FIG. 5A is a filter comprising a
choke coil 63 connected in series with the powerline and a
capacitor 64 connected in shunt with the powerline. The filter
isolates the signal from the remainder of the powerline so that the
information is not conducted to the right of the filter. Not only
will this prevent possible information from being available to a
competitor who might be connected to the same powerline, but it
also makes it possible to use the same powerline for carrying other
signals at the same carrier frequency from a different sender when
another gasoline pump is connected to the powerline. The filter
could be eliminated in the situation where a different carrier
frequency is used for each gasoline pump and where the power
transformer for the station is relied upon to block the pickup of
information by a competitor from the powerline.
A variation of the current forcing technique shown in FIG. 5A is
illustrated in FIG. 5B. In this case, three senders represented by
current generators 59a, 59b and 59c are each connected in series
with current forcing resistances 56a, 56b and 56c, respectively.
Each of these current generators and their series connected
resistances are connected in shunt with the powerline. The
receivers 60a, 60b and 60c for each of the different signal
generators are powered by the same powerline. The current
transformers 61a, 61b and 61c which pick up the input signal for
each of the respective receivers are placed on the same powerline
shunt.
It should be noted at this point that while the invention has so
far been described as senders located at gasoline pumps and
receivers located at a central station, it is also possible to
provide a signal generator at the central station and a receiver at
the pump islands for resetting the computer and turning the power
on and off at each pump from the station. The same powerlines could
be used for a plurality of pumps, and the same carrier frequency
could be used for controlling each pump as is used for transmitting
information such as dollars and cents from the pump to the
station.
Referring now to FIG. 3 of the drawings, the receiver is connected
to the powerline by a coupling network 65 similar to that used at
the output of the sender. Coupling network 65 comprises a coupling
transformer 66 having primary and secondary windings. Connected in
series with the primary winding are a pair of coupling capacitances
67 and 68 each of which is connected in series with a resistance 69
and 70, respectively. A neon indicator lamp 71 may be connected in
shunt with the powerline. Connected in parallel with the secondary
winding of coupling transformer 66 is a capacitance 72 which
together with the secondary winding of the transformer forms a
parallel resonant tank circuit. The tank circuit is resonant to the
carrier frequency.
When more than one pump is connected in the system, it is desirable
to have a high Q tank circuit for selectivity between pumps, i.e.,
between oscillator frequencies. However, a high Q results in the
slow buildups of the signal and ringing or slow decay. This, of
course, seriously distorts the pulse envelope. In order to limit
the effects of ringing of the tuned coupling circuit and provide
good selectivity, the tank circuit is connected to the input of a
logarithmic preamplifier 73. As is known in the art, the property
of such an amplifier is to amplify small amplitude signals greater
than large amplitude signals. This has the effect of "squaring up"
the input pulse burst. The output of the logarithmic preamp 73 is
connected to a tuned amplifier 74 which provides additional gain
and selectivity. This output is connected to a threshold detector
75 which detects the pulse modulation envelope. The pulse output of
detector 75 causes a switch comprising NPN-transistor 76 and
PNP-transistor 77 to be turned on and off synchronously with the
pulse modulation envelope.
The output of the switch is connected to a first pulse with
discriminator 78. This discriminator comprises at its input a pair
of NPN-transistor 79 and 80 which are connected in cascade.
Transistor 79 is turned on by an ON pulse from transistor 77. This
in turn causes transistor 80 to be turned off. Connected in series
across a source of positive voltage and ground are a timing
resistance 81 and a charging capacitance 82. The junction of
resistor 81 and capacitor 82 is connected to the collector of
transistor 80, and when transistor 80 is biased to nonconduction,
capacitor 82 is charged through resistor 81. If the pulse output
from detector 75 is of sufficient duration, approximately 1.9 ms.,
capacitor 82 will charge sufficiently to fire a four layer
threshold device 83 connected thereacross.
A load resistor 84 is connected in series with four layer threshold
device 83 and the voltage produced across this load resistor is
applied to the base of NPN-transistor 85. Transistor 85 in
combination with PNP-transistor 86 forms an electronic switch which
controls another timing circuit comprising timing resistance 87 and
charging capacitance 88 connected in series with the collector of
transistor 86 and ground. If the pulse appearing at the base of
transistor 85 is too long, capacitor 88 will charge sufficiently to
fire four layer threshold device 89 connected thereacross.
Otherwise, capacitor 88 is discharged through resistor 87 and
resistor 90.
The four layer threshold device 89 is connected in series with a
load resistance 91, and the voltage developed thereacross is
applied to the base of an NPN-transistor 92. The emitter of
transistor 92 is connected directly to ground and the collector is
connected to a source of positive voltage by a resistor 93 and a
firing capacitor 94 connected in series. The junction of resistor
93 and capacitor 94 is connected by way of an isolating diode 95 to
the collector of transistor 85. When transistor 85 conducts,
capacitor 94 is discharged through transistor 85 and resistor 94a.
If the pulse at the base of transistor 85 is not too long,
transistor 85 will turn off allowing capacitor 94 to be charged
through resistor 93. The charge accumulated on firing capacitor 94
triggers a retriggerable or integrating one-shot 96. If, on the
other hand, the pulse at the base of transistor 85 is too long,
then four layer threshold device 89 discharges capacitor 88
providing a pulse at the base of transistor 92 which conducts and
prevents capacitor 94 from triggering one-shot 96. So long as the
pulses applied to the input of the integrating one-shot 96 are of
sufficient duration, the output of the one-shot will remain on.
Thus, the one-shot 96 provides an output having a duration of 20
ms. as shown at the bottom of FIG. 4. This output is used to drive
the counter driver and counter 97 which in the specific example is
the dollars counter.
The gallons information is detected in a similar manner with an
identical pulse width discriminator 98 and integrating one-shot 99.
However, since the gallons information is represented by OFF pulses
rather than ON pulses, an inverting transistor 100 is connected
between the switch comprising transistor 76 and 77 and the pulse
width discriminator 98. The output of integrating one-shot 99 is
applied to a counter driver and counter 101 which is the gallons
counter.
It may be appreciated from the foregoing discussion that the pulse
width discriminators 78 and 98 operate to reject both short
duration pulses, such as characteristic of transient noise, and
long duration pulses, which might be generated during equipment
turn off and turn on, and to identify only the desired pulse. A
signal sensing circuit 102 may also be provided. This circuit would
be connected to the output of detector 75 or the switch comprising
transistors 76 and 77 and would serve to enable the counters 97 and
101 only when a carrier is present. The signal sensing circuit then
provides protection against false counting since a discriminator
output alone cannot initiate the counter drive unless the sensing
circuit 102 is on.
In the embodiment described it is assumed that both gallons and
dollar information are to be transmitted. There are many
applications where only dollar information or only gallon
information are needed to be transmitted. These possibilities are
shown in FIGS. 6A and 6B of the drawings which illustrate a four
channel system transmitting only dollars information or only
gallons information. In this situation a different carrier
frequency for each pump is selected. Since only one item of
information is to be transmitted, only one one-shot 21, for
example, is required. The output of one-shot 21 gates a switch 103
which supplies power to a square wave generator 30. The output of
square wave generator 30 gates the output of oscillator 44 through
switch 46 to power amplifier 49. The output of power amplifier 49
is connected to the powerlines 104 through a coupling network 50.
The powerlines 104 comprise a three conductor 230 volt line having
the center conductor grounded. One hundred and fifteen volt service
is thus available across either of the two outside lines and the
grounded centerline. If desired, a filter comprising series
connected choke 63 and shunt connected capacitance 64 may be
interposed between the powerline and the coupling network 50.
At the receiver end, a coupling network 65 couples the signal on
the powerline to a log preamp 73 and tuned amplifier 74. Threshold
detector 75 receives the output from tuned amplifier 74 and
provides a detected pulse output to pulse width discriminator 78.
Since only one item of information is being transmitted by a
particular pump, only one pulse width discriminator is required.
The output of discriminator 76 is applied to integrating one-shot
96 which provides a counting pulse to counter 97. A separate
counter 97 is provided for each pump at the central station when
only dollar information is to be transmitted.
In applications where the information desired is the total number
of gallons sold from a plurality of pumps, the outputs of each of
the integrating one-shots 96, representing quantity delivered by
each of the pumps, are applied to a parallel to serial converter
and one-bit memories 105 which provides an output to a totalizing
counter 106.
A schematic representation of a logic circuit suitable for
providing the parallel to serial converter and one-bit memories 105
is shown in more detail in FIG. 7 of the drawings. Each of the
one-shots 96 from the four channels is applied to a respective
flip-flop memory 107. The output of one-shot 96 is also applied to
one input of a three input AND-gate 109. The output of flip-flop
107 is applied to another input of AND-gate 109. The AND-gates 109
are each strobed by a clock 110 applied to their third input.
Clock 110 comprises a clock oscillator 111 which produces a
symmetrical square wave output as illustrated at the top of FIG. 8.
This square wave output is applied to inverter 112 in order to
shift the phase of the output 180.degree.. The phase shifted clock
oscillator output is then applied to a counter 113 which in its
simplest form may be a four stage ring counter. Counter 113
produces a four phase clock or strobe which applies a pulse to
one-shots 108 to produce a pulse of short duration (as compared to
the duration of the strobe pulse) which is applied to the AND-gates
109 at uniform intervals as illustrated in FIG. 8 to ensure that
pulses are evenly spaced at input of OR-gate 115. The frequency of
clock oscillator 111 is sufficient to strobe each AND-gate 109
twice for each input pulse from its one-shot 96.
In operation, if a pulse is generated by one-shot 96 at a time when
there is no strobe input to AND-gate 109 from counter 113,
flip-flop memory 107 will be set. The output of flip-flop 107
enables AND-gate 109 until it is reset. When a strobe pulse later
appears from counter 113 it is passed by AND-gate 109 to trigger
one-shot 114. The output of one-shot 114 resets flip-flop 107 and
is also connected to OR-gate 115. OR-gate 115 is a four input OR
gate, receiving one input for each channel in the system. The
output of OR-gate 115 sets a flip-flop 116. Flip-flop 116 is reset
by the output of clock oscillator 111. Thus, flip-flop 116 is
caused to toggle back and forth with a frequency that depends upon
the rate at which gallons information is applied to all of the
several channels of the system. The outputs of flip-flop 116 are
each connected to respective driver circuits 117 and 118. These
driver circuits each are operative to energize a respective winding
119 or 120 of a stepper motor 121. The stepping motor 121 has a
mechanical output drive which drives the totalizer counter 106.
Where a pulse is generated by one-shot 96 at the same time as there
is a strobe input to an AND-gate 109 from counter 113, AND-gate 109
will not pass a signal to trigger one-shot 114 and the pulse is not
then passed to OR-gate 115. Neither is flip-flop 107 reset.
However, since the frequency of clock oscillator 111 is sufficient
to strobe AND-gate 109 twice for each input pulse from one-shot 96
at the maximum pulse repetition rate of the pulsers in the pumps,
counter 113 will cycle twice between the receipt of two consecutive
bits of information from the same source. As a result, on the next
cycle there will be no output pulse from one-shot 96 and the strobe
pulse from counter 113 will be passed to trigger one-shot 114 and
reset flip-flop 107. Thus, only one-bit memories are required to
prevent the loss of any bit of information thereby ensuring that
the total count at counter 106 is accurate.
In its most comprehensive form, the invention would comprise the
transmission of both dollars and gallons information as
particularly described with respect to FIGS. 2 and 3. In addition
the system would also include a totalizing output for either
dollars or gallons or both. For example, it is possible to provide
the attendant on duty in the station with price information from
each pump and at the same time provide total gallons information
for purposes of inventory control.
As stated previously, it is also possible to provide a sender at
the station and a receiver at each pump. This is illustrated in
FIGS. 6A and 6B by the blocks 122 and 123 labeled "reset." Block
122 in this case would be a sender and block 123 would be a
receiver similar to those described in detail with respect to FIGS.
2 and 3. The purpose of such a provision would be to allow the
attendant to have complete control of the pumps from the station.
Specifically, the attendant could use the resets to make power
available at the individual pumps only when he wishes to authorize
a customer to use the pump.
As will be apparent to persons skilled in the art, various
modifications, adaptations and variations of the foregoing specific
disclosure can be made without departing from the teachings of the
present invention.
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