MXPA97000573A - Fuel distributor equipment temperature compensator - Google Patents

Abstract

An apparatus (10) for dispensing liquid fuel comprising a meter (70) for measuring the volume of fuel distributed, a temperature sensor (80) for determining at what temperature the volume was measured, and processing means for taking the temperature into account with object of providing the same calorific content per unit of fuel distributed

Description

FUEL DISTRIBUTOR DEVICE TEMPERATURE COMPENSATOR BACKGROUND OF THE INVENTION The present invention relates to improvements in fuel dispensing devices to allow compensation of the measured amount of fuel supplied to compensate for temperature fluctuations. As is known from elementary physics, the volume of most objects depends on temperature, with most things expanding when they heat up and contracting when they cool. This is true of liquid fuels such as gasoline. Since liquid fuels are typically sold by volumetric measurement, such as US gallons, Imperial gallons, or liters, the mass of fuel sold in, for example, a US gallon at 30 degrees Fahrenheit will differ from the mass sold at 90 degrees Fahrenheit. Since the actual energy or calorific value depends on the mass, the fuel value of the transaction depends on the temperature. The various government bodies with oversight of trade weights and measures have from time to time required this to be taken into account, as reported in US Pat. No. 4,101,056 to Mattimoe, the entire disclosure of which is incorporated herein by reference.

However, this is a problem that has not been addressed to provide a commercially viable temperature compensating fuel dispensing apparatus. The problem is to make the quantity sold by volume normalize to a standard temperature, so that, for example, the energy value of a "unit" of fuel at 0 ° C is the same as a fuel unit at 30 ° C. ° C. One of the problems encountered is the problem of taking an exact temperature. There are several factors that affect the temperature of the fuel, including the ambient temperature, temperatures of the previous environment, isolation of the fuel from the environment, possible heating by pumping the fuel, and the like. Also, the temperature must be taken on a real-time basis, since there may be inhomogeneities in the temperatures of the stored fuel, so that the actual fuel temperature may vary during a fuel supply transaction. Finally, the fact that the product involved is highly flammable must be taken into consideration. Any sparking or production of electric arc in the electronic components used to take the temperature could be disastrous. The requirement to accurately detect the temperature in a hazardous location imposes several constraints. Since temperature sensors are in the vicinity of gasoline, the sensors must be either intrinsically safe or explosion-proof to meet the requirements of the security agencies. The problems with an explosion-proof system are the cost of the conduit or mineral insulation cable, difficulty in handling during installation, and finding a space to locate an explosion-proof box. Generally, explosion-proof items are very large and heavy. The multiple explosion-proof sensors also complicate a congested hydraulic area and would be very difficult to adapt. The temperature readings require a high degree of accuracy and stability to maintain the approval of the Weights and Measures authorities. As a result, it is valuable to have a system that provides temperature measurements with minimal errors for an indefinite period of time. The electronic and mechanical components will widen with time and temperature, causing associated widening in the temperature readings, although this could be compensated with conditions and other calibers for gains and zero adjustments, these can be mismatched, they can also change with the time, and require that time, tools and equipment be adjusted.

According to the foregoing, there is a need in the art for a verifiable, reliable, trouble-free, accurate dispensing apparatus that corrects the volume readings to compensate for temperature fluctuations. SUMMARY OF THE INVENTION The present invention provides an apparatus for distributing a liquid fuel comprising: a housing having a fuel handling compartment, an electronic compartment, and a vapor barrier between the fuel and electronic handling compartments; a plurality of fuel passages through the housing; and flow meters for each passage to measure the volume of fuel flowing through the passages, each meter connecting to a first electric circuit to receive a signal representative of the volumetric flow through its respective passage, characterized in that it also comprises thermometric probes associated with respective passages to determine the temperature of the fuel flowing through the passages, each of the probes connecting to a second electric circuit common to each probe to receive signals representative of the temperatures of the probes and process those signals for transmission on an intrinsically safe transmission path, common, through the vapor barrier to the electronics compartment; and the electronics including a computing device connected to the circuits, first and second, to receive the signals coming from the circuits, first and second, and to generate an output signal representative of a volumetric flow of corrected temperature. Preferably, each flow meter includes a thermometric probe mounted on a removable terminal wall of the meter housing. Preferably, the end wall also includes a perforation adapted to receive a second probe in order to verify the accuracy of the first mentioned probe in the terminal wall. The probe can be a resistive temperature detector (RTD) probe. The second electric circuit can convert the data and reference signals to a pulse-amplitude modulated form. If so, it is preferred that the pulses of the converted data and the reference signals are of the order of 20-50 milliseconds in length. Preferably, at least four of the probes are electrically connected to the second electrical circuit. The second electric circuit can include a sawtooth waveform generator and a comparator to compare the voltage across one of the probes with a sawtooth waveform to generate pulses of a length derived from the resistance of the probe. Preferably, one of the reference resistors has a resistance corresponding to the resistance of the probes at an extreme end of a range of expected temperatures, and the other of the reference resistors has a resistance corresponding to the resistance of the probes at one end opposite of the range of expected temperatures. In a preferred embodiment, the data and reference signals are transmitted to the electronic compartment and the temperatures of the probes are calculated by interpolation of the data signals and reference signals. The errors of the non-linearity of the resistance of the probes can be compensated for by the use of a table of search for resistance values for temperatures in the expected temperature range, and the finding of the corrected values in the table for interpolation. The invention also provides a method for distributing liquid fuel and measuring the amount distributed according to the corrected volumetric temperature measurement comprising: the passage of the fuel through a plurality of fuel passages in a hazardous area of a fuel dispensing apparatus; the generation of a signal representative of the volume of fuel flowing in the passage; and the passage of the signal representative of the volumetric flow through an intrinsically safe passage through a barrier to a non-hazardous area, characterized in that it also comprises the steps of: generating a signal representative of the temperature of the fuel flowing through the passage; receiving the representative temperature signal and transmitting the temperature data through the barrier through an intrinsically safe transmission path, common to a plurality of temperature sensors associated with respective fuel passages to the non-hazardous area; and modify the signal representative of the volumetric flow to give a temperature ratio. In one embodiment, the method includes the temporary insertion of a temperature probe juxtaposed to the passage to verify the accuracy of the signal representative of the temperature of the fuel flowing through the passage. Preferably, the method includes the sequential passage of a current pulse from a current source through each of the various reference probes and resistors to generate data signals representative of the temperature of the fuel flowing through the passage and other passages and to generate reference signals. The method may include multiple transmission of the data and reference signals for transmission through the intrinsically safe passage through the barrier to the non-hazardous area. The method can also include the conversion of the data and the reference signals to a pulse-amplitude modulated shape with the pulses in the order of 2-50 milliseconds in length. In the method, high-frequency momentary currents can be filtered from the data and reference signals in the non-hazardous area. Preferably, the step step includes the passage of current pulses through at least four probes. The method can include the generation of a sawtooth waveform and the comparison of the voltage across the probes with a ramp voltage of the sawtooth waveform to generate pulses of a length derived from the resistors of the waveform. probe. Preferably, the step of passing a current pulse through the reference resistors generates a voltage corresponding to the voltage across one of the probes at an extreme end of a range of expected temperatures. Also, the current through the other reference resistor generates a voltage corresponding to the voltage across one of the probes at the other end of a range of expected temperatures. Preferably, the temperatures of the probes are calculated by interpolation of the data signals and the reference signals. Also preferably, the errors of the non-linearity of the resistance of the probes can be compensated by using a search table of resistance values for temperatures in the expected temperature range, and finding the corrected values in the table for interpolation. BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a partially exploded view of a fuel dispensing apparatus according to a preferred embodiment of the invention showing internal components in schematic form, - Figure 2 is a block diagram of the main components of the temperature compensation system of the embodiment of Figure 1; Figure 3 is a perspective view, partially enlarged, of a preferred meter mode; Figure 4 is a block diagram of the components of the meter-T board of the embodiment of Figure 1; Figure 5 is a block diagram of the interface between the meter-T board and the ATC controller; Figure 6 is an operation timing diagram of the meter-T board; and Figure 7 is a timing diagram showing the generation of pulse amplitudes modulated in the operation of the T-meter board. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 1, a fuel dispensing apparatus 10 of conventional design is shown, except as described herein. In particular, the dispensing apparatus 10 may take the form of a modified version of a THE ADVANTAGE Gilbarco dispensing apparatus, sold by Gilbarco, Inc. of Greensboro, North Carolina. The housing 12 is divided into a fuel handling compartment 14 and an electronic compartment 16 by a barrier 18. The dispensing apparatus 10 is shown mounted on the floor with pipe connections 20, 22, 24 extending upwards from the underground tanks to supply liquid fuel, typically gasoline to the distributor apparatus. These inlet pipes 20, 22, 24 have respective meters 26, 28, 30 in line with them and supply downstream pipes 38, 40, 41. Each of the downstream pipes leads to a hose 42 (only one of which shown for reasons of simplicity) ending in a nozzle 44. The nozzle 4, when not in use, rests on a nozzle rest handle 46. When fuel is about to be pumped, the nozzle 44 is removed from the housing of the distributor apparatus 12. and the handle 46 moves, closing a switch, which is indicated to the hydraulic interface board 62 in a conventional manner. The measuring devices 26, 28, 30 are preferably in a conventional form of a meter with attached impeller. The meter is modified slightly as shown in Figure 3, as will be discussed in more detail hereafter. Each of the impellers supplies an output signal indicative of the liquid flow rate through the meters on the pipes 32, 34, 36. These are communicated to an automatic temperature compensation board 60 at the top of the housing 12. Intrinsically, the security passages of 17 on the barrier 18 allow communication on the electrical wiring from the fuel handling compartment 14 to the electronic compartment 16. The barrier 18 is a conventional design, such as that used in the THE ADVANTAGE® distributors sold by Gilbarco, Inc., provided for the purpose of providing a safety separation between the components below the barrier, which currently handle the flammable liquid fuel and the electronics above the barrier. This increases security at an added level of protection. It will be less likely that an electronic fault that causes a spark ignites any fuel vapor. The passage 17 is an electronic circuit that includes voltage limiting devices such as Zener diodes, and current limiting devices, such as resistors or fuses, as seen in Figure 5. In this way, a fault in the circuit could happen only a limited amount of power to the components below the barrier 18. In a preferred embodiment, not shown, the impellers are attached to the gauges using the technique employed in the THE ADVANTAGE® distributors sold by Gilbarco, Inc., and well known in the matter. In this type of dispensing apparatus, each meter is below the barrier 18 and its associated impeller is above the barrier 18. A rotating shaft through the meter passes through the barrier to direct the impeller. In this way, the pipes 32-36 from the impellers to the board 60 are located only above the barrier 18. Each of the measuring devices 26-30 is also supplied with connection 50, 52, 54 to a board meter-T 56 in the fuel handling compartment. Connections 50-54 provide indices of the temperature of the liquid fuel passing through the respective measuring devices 26-30, as will be discussed in more detail hereafter. The meter board-T 56 combines the data from the pipes 50-54 in a modulated form of pulse amplitude in series and communicates this signal along the pipe 58 through an intrinsically safe passage 17 to the ATC board 60 The ATC board is also provided with connections to a hydraulic interface board 62 and to a pump control board 64, which, in turn, is connected to the hydraulic interface board 62. An output of board 60 is applied to the board. 66a visual display screen on the outside of the housing to show the customer the correct volumetric reading of the fuel he is acquiring. A similar deployment screen 66b on the other side of the distributor apparatus (not shown in Figure 1) receives the pertinent data to the hoses on that side. Of course, the corrected volumetric data can also be supplied to any of the various remote consoles and the like as conventional in modern fuel dispensing apparatuses. Figure 2 shows in block diagram form the important functional components of the automatic temperature compensation system. The temperature probes 80 embedded in the measuring devices 26-30 supply data to the T-56 meter board. The serial data was emitted through the intrinsically safe connection 17 to the ATC 60 controller board. The ATC controller board 60 receives unprocessed volumetric data from impellers 26-30. Board 60 takes the temperature data supplied from the T-56 meter board to make corrections to the raw data from the 26-30 impellers and supplies the corrected output to the 66a and 66b display screens, according to the side of the housing of the distributor apparatus 12 that is being accessed by a customer. The ATC controller board also communicates with the hydraulic interface or mixer controller board 62, which in turn communicates with the pump controller board 64 in a conventional manner.

The hydraulic interface board also communicates with the handles 46, valves and the switch for submerged turbine pumps in the underground tanks, from which the 20-24 pipes separate the liquid fuel. Figure 3 shows an improved meter 70 for use in measuring devices 26-30. The meter 70 is a conventional meter except that one of its end caps 74 has been modified to provide temperature measurement data. The cover 74 is fused with two permanently installed perforations 76, 78. A permanent wall 76 is, in fact, an opening towards the interior of the meter 70, since the perforation 78 forms a hollow tube depending on the meter 70. A The temperature sensor 80 is permanently secured in the perforations 76 to be directly exposed to the fuel as it flows through the meter 70. In this way, a direct measurement of the fuel temperature can be obtained by the sensor 80. The perforation of test 78 is provided as a receptacle for a thermometer of the examination authority. The test perforation 78 can be filled with a thermally conductive material to ensure a good thermal connection between the thermometer and the housing to allow verifications as to the accuracy of the temperature that is being provided by the sensor 80. This design is particularly useful because to which allows easy adaptations of existing meters in the field. The system will now be described with reference to the block diagram of Figure 2, and with reference to the technology already well known to those of ordinary experience in the art in the form of existing THE ADVANTAGE® distributors. This board also communicates with the display screens 66a and 66b. It controls the deployments during ATC mode, and allows the Pump Controller Board 64 to control the display screens during normal mode. The temperature measurement is controlled by the ATC Meter-T Board. It has the potential to monitor one to eight different product probes 80, plus a ninth probe for ambient temperature. The board measures the voltage sequentially through each of the probes. This voltage and the output of a low frequency sawtooth waveform generator are input to a comparator whose output is a pulse amplitude proportional to the voltage across the probe. This board also contains high precision references for self-calibration. The Pump Controller Board 64 receives compensated pulse data from the ATC 60 Controller Board. This is the same controller board used in conventional Gilbarco THE ADVANTAGE® units. No changes need to be made to the software or hardware of the Pump Controller Board when communicating with the ATC system. In order to make the Meter-T Board and the probes intrinsically safe, the power supplied to the Meter-T Board from the ATC Controller Board, and the newly received temperature data, is passed through the intrinsically safe barrier 18. This barrier resembles the standard impulse IS barriers of commercially available dispensing devices. The packing of the Meter-T Board and the probes would have to be otherwise explosion-proof and, consequently, very expensive. Each probe 80 is installed in a product flow path in order to measure the temperature of the product. Each probe 80 uses an almost linear, highly accurate RTD, and four wire measurement methods and is regularly scanned by the ATC 56 T-Meter Board, which converts the voltage measurements across the probes into amplitude temperature data. of time domain impulse. The Hydraulic Interface Board 62 is used by the Pumping Controller Board 64 in unmixed configurations to directly communicate with and control hydraulic devices. In the ATC system, pumping handling signals are entered directly on this board; however, the impulse data received are the compensated pulses emitted by the ATC 60 Controller Board. Each of these input sets is converted back to logical CMOS levels and then passed to the 64 Pumping Controller Board. All other pipelines hydraulic control; that is, valve and STP control are passed directly from the Pumping Controller Board to the Hydraulic Interface Board, as is conventional. In a mix pumping configuration, the Mixer Controller Board exists in place of the Hydraulic Controller Board. However, the functionality with respect to the ATC system remains constant. The low and high product pulses from each side are fed directly to the ATC controller board, whose level is lowered, compensates, then raises the pulses as it would in a non-mixer. The pulses are then fed to the Mixer Controller Board. Submerged Turbine Pumps, proportional valves and pumping handles are still routed directly through the Mixer Controller Board.

Interface A This interface contains deployment outputs from the Pump Controller Board to the ATC Controller Board, and strobe outputs from the Modular Keypad and explores the inputs to the Pump Controller Board from the ATC Controller Board. Interface B The ATC controller maintains the final control of the displays with this interface. The data signals and the transfer validation signals are such as those coming from the Pump Controller; however, the ATC Controller determines whether its own data or data from the Pump Controller are sent to the Main Deployment Screens. Interface C This interface passes through the return signals and keyboard strobes that are normally handled by the Pump Controller. However, the Modular Keypad is also used to control ATC functions. The ATC Controller Board searches the keyboard signals of the Pump Controller Board, determines which key was pressed, and then takes control of the display screens if necessary. Interface D This interface contains all the normal hydraulic signals between the Interface Board Hydraulic and Pumping Pump Board. The impulse data transmitted here will have been previously compensated by the ATC Controller Board. Interface E This interface contains the standard pump control signals, the hydraulic control pipe signals and the STP controls used in Modular Electronic Distribution Units without ATC. However, the impellers are connected directly to the ATC Controller Board. Interface F This interface contains pulse data compensated by the ATC Controller Board, the level moves to resemble the normal inputs of the Hydraulic Interface Board. The voltages are sufficiently raised by the ATC Controller Board to reliably switch the input transistors on the Hydraulic Interface Board. Interface G These are unbalanced impulse signals, sent directly by the impellers to the Board ATC controller. These are the same impulse signals used by the Hydraulic Interface Board in a modular dispenser or THE ADVANTAGE without ATC, and are represented as pipes 32-36 in Figure 1. Interface H This is a "serial" interface of a only channel in the ATC Controller Board and the ATC Meter-T Board, through which the T-Meter Board transmits temperature data to the controller as an impulse whose amplitude is related to the temperature. The Meter-T board continuously transmits a sequence of up to eleven pulses to the Controller Board. One pulse is sent per product temperature probe (up to eight maximum). An optional ninth pulse corresponds to the room temperature sensor. For a two-product, two-sided dispensing device, there will be four product probes. Two high-precision reference data pulses must also be transmitted through this interface to allow the ATC Controller to self-calibrate the system as potentially the tenth and eleventh impulses, respectively. Interface K This interface contains the type authorization signals issued from the Board (Mixing Controller) of the Hydraulic Interface for the ATC Controller Board. During the ATC Transaction Mode (see THE ADVANTAGE® ATC Software Functional Specification), the ATC Controller Board uses the impeller inputs to determine the product selection, but uses the grade authorization information to determine when it is finished. the transaction. TABLE METER-T 56 The meter board-T 56 sequentially reads up to 9 temperature probes 80 and 2 reference elements by applying a constant current and then measuring the voltage drop. The fall Voltage is directly related to the resistance of the probe or element that is being measured at that moment. The voltage drop is amplified and compared with a stable free running ramp voltage to create an impulse amplitude proportional to the amplified voltage drop. Each temperature probe and each of the two reference resistors creates its own pulse amplitude due to the conversion. The resulting pulses are transmitted sequentially through the external security barrier 17. In addition to the pulse creation function described above, there is a probe current detector 100 that inhibits the creation of an output pulse when a current is not received from the probe being read. The output pulses are assembled in a pulse train that has a particular sequence for easy retrieval. In the ATC system, the pulses are in the sequence: Low Reference, High Reference, Probe 1, Probe 2, Probe 3 ... to Probe 9. There is also an inactive time in the pulse train after the last probe that provides an additional key for synchronization in the receiver. By setting the system so that pulse durations are typically 20 to 50 milliseconds, the system can provide a good degree of noise immunity. In a typical application, the data pulses are in a conduit with basic line voltages of 120 or 240 vac. Typically, line voltages carry momentary currents that last for periods ranging from nanoseconds to microseconds. The data pulses of the ATC system can be hard filtered to remove these noise pulses without substantially affecting the data. Since filtering affects both the calibration pulses and the probe pulses in the same way, there is no net effect that can contaminate the validity of the data. For example, if the filtering action adds 50 microseconds to the duration of the impulse, all the pulses are lengthened by 50 microseconds, and the data contained in the negative proportions of the impulses will remain the same. Referring to Figure 4, which is a block diagram of the meter board-T 56, the Ramp Generator 102 uses an integrator to create a very linear ramp voltage. An output level detector detects high and low voltage conditions, which provides up / down control to control the direction of the ramp. The output of the ramp generator 102 is a ramp that rises for approximately 100 milliseconds, and falls for approximately 20 milliseconds. The part or bottom of the ramp is approximately 3 volts and the top of the ramp is approximately 9 volts. The ramp is of free execution, and is not intentionally influenced by any external input. The ramp provides a mechanism for linear conversion from 5 voltage to time. In other words, the length of time between two points on the ramp is proportional to the "'voltage difference between the same two points as shown in figure 7. The ramp should be stable in ramp ratio over periods of seconds, but the 0 widening over long periods over periods of hours or days are acceptable, since the reception system ignores the effect of slow broadening A Current Source 104 provides a nominal current of 1 milliamp without taking charge 5 into account and is routed through a selected multiplexer 110, 112, 114, 116 .. according to the control of the state generator and the decoder 108. The State Generator and Decoder 108 receives a ramp address control signal developed in the ramp generator 102, and transforms it into a digital signal by means of a Schmitt activator, whose output is high during the time of the ramp, when that output goes down at the end of each ramp period, it activates the synchronization input of a binary counter, which advances an output a binary. Accordingly, a synchronization sequence is developed to control the various multiplexers 110, 112, 114, 116 ... and to control the total pulse sequence with respect to the dead time and the continuous process of creating a pulse train. The operation of a "window" for each of the resistors and probes referred during the sequential ramp cycles is illustrated graphically in Figure 6. During that window, the current coming from the source 104 is directed towards the chosen resistance and the fall The resulting voltage is applied to the amplifier 106. The multiplexers 110, 112, 114, 116 (and more as needed per probe and each for the reference resistors) provide connections to each probe element or calibration resistor, depending on the particular multiplexer. When the control inputs are low, the multiplexer works like a 4-pole relay with open connections. When the control inputs are high, the multiplexer works like a 4-pole closed relay. Under the control of the State Generator and Decoder 108, one multiplexer is enabled at a time. When enabled, each multiplexer connects the current source, the current return, the probe + detector, and the probe detector - in a 4-wire measurement configuration. This provides the highest accuracy in measuring the voltage drop across the resistive element that is being examined at that moment, since the voltage drops in the lead wires of the current source and the current return are excluded from the measurement. Resistors LO Real and Hl Real 130, 132 represent reference resistors that are used for system calibration. The Real LO is chosen at the lower end of the full scale temperature range, and the Real Hl is chosen at the high end of the full scale range. In the T-meter, LO Real is 80.1 ohm, and Real Hl is 120.3 ohm, although other values could be used. The tolerance and stability of these resistors is selected based on the application, since the accuracy of the system and the long-term stability ultimately depend on these resistors. In the T-meter, this one has .01% tolerance and 5 parts per million of temperature stability, they are still available as commercial parts. A Voltage Difference Amplifier 106 consists of an instrumentation amplifier with a voltage gain of about 60. There is filtration on both the input side and the output side of the amplifier stage to reduce the susceptibility to noise. The amplifier recovers the measured voltage drop from the resistive element that is being detected and amplifies the CE signal for later use. The impedance of the amplifier input is very high to avoid the effects of errors due to the resistance of lead wires coming from the amplifier towards the element. Since the nominal input is in the range of 80 to 120 millivolts of ce, the corresponding output of the amplifier is in the range of 4.8 to 7.2 volts of ce, during probe detection or resistive element detection. The reset block 118 zeroes the input and output voltages of the amplifier block at the top of each ramp. At the end of each ramp formation period, a negative impulse is coupled to the input of the Replenishment Block, which causes a momentary shortening of the input of the amplifier block, and discharges to the base. This action ensures that each new amplifier output starts at a nominal level of zero volts. This depletes the voltage that was in the capacitors due to the last reading. In the case of a conductive sensing cable broken from the probe, the previous reading would continue to be read without this reset function. The Reset Block is also activated by detecting a missing probe, as soon as it is detected by the Probe Current Detector 100. This provides for low maintenance of the amplifier output as long as the nominal current limits of the amplifier are not met. probe returned. This provides information to the system that takes into account missing or defective probes. The current returning to the Probe Current Detector 100 from the probe 80 of its multiplexer must be at least 250 microa nominal perios to turn on. In the event that a probe having a broken lead wire in the source or return path is selected, the current detector responds by causing a reset of the amplifier output to occur for the duration of that synchronization period of the amplifier. multiplexor. The Comparator Block Low 120 includes a resistive divider. The voltage divider provides a nominal voltage of approximately 3.5 volts of ce. The purpose of the Low Comparator block is to provide a consistent starting point for the output pulses generated by the T-meter board. The comparator compares the ramp formation voltage with the 3.5 volt level and outputs a digital output 0 when the ramp voltage is greater than 3.5 vdc, and a digital output 1 when the ramp voltage is less than 3.5 vdc. This method is used to create the starting point, because irregularities in the ramp ratio occur at the bottom of the ramp when the ramp changes direction. The Comparator Raised Block 122 compares the output of the amplifier block with the ramp voltage and outputs a digital output l when the output voltage of the amplifier is greater than the ramp voltage, and a digital output 0 when the output voltage of the amplifier is smaller. to the ramp voltage. The results of such a comparison for various probe resistances can be seen in Figure 7. The Impulse Generator Rocker Circuit 124 responds to signals from comparators 120, 122, low and high, to generate an upward pulse. The impulse starts at the point determined by the low comparator and ends at the point determined by the high comparator. The low comparator establishes the tilting circuit, and the high comparator sets the tilting circuit to zero. The Dead Time Generator 126 is used to synchronize the system that receives the data clearing.

Each data clearing causes the sequential scanning of each resistor or resistive element followed by a dead time. The Output Pulse Interface 128 provides a low impedance path to the base, allowing the flow of current from an external circuit when the pulse generator sends a pulse to the output circuit. The duration of the current flow is directly related to the time period between the starting point on the 3.5 vdc ramp, and the termination point on the ramp which is determined by the insertion of the ramp and the output of the amplifier. EC. In this particular system, the output switches a nominal current of approximately 25 to 30 milliamps. In this manner, the T-meter 56 emits a pulse train on the pipe 58, with the pulses in a prescribed sequence as established by the static generator and decoder 108. The pulses are of an amplitude determined by the resistance of the probe selected 80 or reference resistors 130, 132. The resistance of each probe 80 is, of course, highly dependent on the temperature of the meter in which it was installed. Referring now to Figure 5, the output of Meter Board-T 56 to the ATC Controller Board 60 will be explained. The supply current of the combined T-meter plus the switched data pulse current is monitored by the input current sensing resistor 150. The voltage developed through the sensing resistor is filtered by a low-pass network 152 to remove the noise components that are introduced into the data channel. In this case, the data channel is the conduit that also contains the AC line voltage. The filtered voltage is compared in the comparator 154 with a reference voltage to determine if the received current is greater than a specific threshold level. The threshold current is chosen approximately halfway between the supply current of the T-meter and the combination of the supply of the T-meter plus the data impulse current. When the received current is greater than the threshold current, the LED 156 in the optical coupler is energized. The optical coupler isolates the logic system from the front end of the receiving circuit to provide both increased safety in the event of faults between the data lines of the T-meter and the AC wiring, and also provides increased noise immunity for noise in the CA line The phototransistor 158 in the optical coupler communicates to the digital hardware. When the LED is on, the phototransistor also turns on, deriving the discrete transistor base to the ground. The transistor collector is in a high state, which results in a high condition at the input of gate AND 160 during this time. In addition, during this time, gate AND 160 receives a clock signal of 384 KHz from oscillator 162 and a frequency divider 164. As a result, the AND gate produces an output pulse train of 384 KHz as long as the current of total data exceeds the threshold current. The number of cycles in the pulse train is counted by the counter 166, and the period between the pulse trains is also measured to determine the presence of the dead time for synchronization purposes. The probe resistance value is extracted by collecting the counts for the Real LO, Real Hl, and any other probe that connects. This count is then compared to the resistance values for the temperatures in the expected temperature range in a search table. This allows errors in the non-linearity of the resistance of the probes to be compensated. The compensated value for the probes and the compensated values for the two known known resistors of Real LO and Real Hl are interpolated to find the temperature as soon as each probe is queried. This process is done for each data clearing, start at LO Real, Hl Real and end of the last probe, which is followed by a dead time. As a result, a new probe resistance is accurately determined at intervals of about 1 to 1.5 seconds. The ATC Controller Board 60 can then select the pulse corresponding to the measuring device 26-30 to determine the appropriate temperature correction of the reading it gives. The resistance is used as an entry in a search table that converts it into temperature, which also interpolates a high degree of accuracy. The use of the search table removes the errors caused by the non-linearity of the resistance of the probes 80 over the expected temperature range. This allows a simple mathematical interpolation of the value for the probes and the reference resistors of the search table to reach a temperature value. The temperature is then used in a conversion process that either adds or subtracts events in the combustion flow count process to compensate for temperature the reported fuel transaction. The overall merits of the ATC system described here are comparative cases of installation in either new constructions or adaptations, a method for detecting what inherently maintains accuracy with minimal spreading, and a method for communicating several exact readings across a barrier of intrinsic safety with minimal effect due to the barrier. The ATC detection system described here essentially removes all the effects of broadening over time and temperature. The system accomplishes this by sending reference readings along with the various temperature probe readings. This process provides the correct interpretation of all readings when using stable references as guide lines. Another benefit of this approach is that the system does not require calibration, and therefore can not be de-calibrated. Although the invention has been described with reference to a particular embodiment, those of ordinary skill in the art will understand that various modifications and refinements may be made and still fall within the scope of the claims.

Claims (26)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. An apparatus for dispensing a liquid fuel comprising: a housing having a fuel handling compartment, an electronic compartment, and a vapor barrier between the fuel handling compartments and the electronics; a plurality of fuel passages through the housing; and flow meters for each passage to measure the volume of fuel flowing through the passages, each meter connecting to a first electric circuit to receive an electrical signal representative of the volumetric flow through its respective passage, characterized in that it also comprises probes thermometric associated with the respective passages to determine the temperature of fuel flowing through the passages, each of the probes connecting to a second electric circuit common to each probe to receive the signals representative of the temperatures of the probes and process those signals for transmission over an intrinsically safe common transmission path through the vapor barrier to the electronics component; and the electronics including a computing device connected to the circuits, first and second, to receive the signals coming from the circuits, first and second, and to generate an output signal representative of a volumetric flow of corrected temperature. The apparatus according to claim 1, characterized in that it comprises a reference resistor also connected to the second electrical circuit whose second circuit receives the signals coming from the resistor for transmission over the common transmission path towards the electronic compartment. The apparatus according to claim 2, characterized in that the second electric circuit sequentially passes a current pulse from a current source through each of the probes and resistors. The apparatus according to claim 2 or 3, characterized in that the second electric circuit multiplexes the data and reference signals for transmission to the electronic compartment. The apparatus according to any of claims 1 to 4, characterized in that each flow meter includes a meter housing and the respective thermometric probe is mounted on a removable terminal wall of the meter housing. 6. The apparatus according to claim 5, characterized in that the end wall also includes a perforation adapted to receive a second probe in order to verify the accuracy of the first mentioned probe in the terminal wall. The apparatus according to any of the preceding claims, characterized in that each probe is a resistive temperature sensing probe (RTD). The apparatus according to any of the preceding claims, characterized in that it has at least four passages of fuel through said housing. The apparatus according to any of the preceding claims, characterized in that the second circuit comprises a pulse-amplitude modulator that converts the received signals into a data stream modulated by pulse-amplitude. The apparatus according to claim 9, characterized in that the pulses of the converted data and the reference signals are in the range of 20-5 milliseconds in length. The apparatus according to claims 9 or 10, characterized in that said second electric circuit includes a waveform generator in a closing tooth and a comparator to allow comparison of the voltage through one of said probes with a waveform in Closing tooth to generate pulses of a length derived from the resistance of the probe. 12. The apparatus according to any of the preceding claims, characterized in that it comprises a reference resistor having a resistance corresponding to the resistance of the probes at an extreme end of a range of expected temperatures. The apparatus according to claim 12, characterized in that it comprises an additional reference resistor having a resistance corresponding to the resistance of the probes at an opposite extreme end of said range of expected temperatures. The apparatus according to claim 2 or any claim dependent thereto, characterized in that the temperatures of the probes are calculated by interpolation of the signals from the probes and the reference resistors. The apparatus according to claim 14, characterized in that the signals are applied to a look-up table to derive the values that remove the errors from the non-linearity of said probe resistance. 16. A method for distributing liquid fuel and measuring the amount distributed according to a corrected volumetric temperature measurement comprising; passing the fuel through one of a plurality of fuel passages in a hazardous area of a fuel distributor; generate a signal representative of the volume of fuel flowing in the passage; and passing the representative signal of the volumetric flow through an intrinsically safe passage through a barrier to a non-hazardous area, characterized in that it also comprises the steps of: generating a signal representative of the temperature of fuel flowing through the passage; receiving the signal representative of the temperature and transmitting the temperature data through the barrier through an intrinsically safe transmission path common to a plurality of temperature sensors associated with respective fuel passages to the non-hazardous area; and modify the signal representative of the volumetric flow to give a temperature ratio. A method according to claim 16, characterized in that it further comprises the sequential passage of a current pulse from a current source through each of the various reference probes and resistors to generate the data signals representative of the temperature of fuel flowing through the passage and other passages and to generate reference signals. A method according to claim 17, characterized in that it further comprises the multiple transmission of the data and reference signals for transmission through the intrinsically safe transmission path through the barrier to a non-hazardous area. A method according to claim 17 or 18, characterized in that said modification step includes the application of data and reference signals to a look-up table to derive the values in order to remove the errors of the non-linearity of the resistance of the probes A method according to claim 17, 18 or 19, characterized in that it further comprises the conversion of the data and the reference signals to a pulse-amplitude modulated form. 21. A method according to claim 20, characterized in that the pulses are in the range of 20-50 milliseconds. 22. A method according to any of claims 17 to 21, characterized in that it further comprises the generation of a sawtooth waveform and the comparison of the voltage across the probes with a ramp voltage of the waveform in tooth of saw to generate pulses of a length derived from the resistances of the probes. 23. A method according to any of claims 17 to 22, characterized in that the step of passing a current pulse through the reference resistors generates a voltage corresponding to the voltage across one of said probes at an extreme end of a range. of expected temperatures. 24. A method according to claim 23, characterized in that the step of passing a current pulse through the reference resistors generates a voltage corresponding to the voltage across one of said probes at the other end of a range of expected temperatures. 25. A method according to any of claims 17 to 24, characterized in that it comprises the calculation of the temperatures of the probes by interpolation of the data signals and the reference signals. 26. A method according to any of claims 16 to 26, characterized in that it further comprises the temporary insertion of a temperature probe juxtaposed to the passage to verify the accuracy of the signal representative of the temperature of the fuel flowing through the passage.