JPH02500223A - Digital conversion device and method for improving output of two-wire transmitter - Google Patents

Abstract

An existing analog two-wire transmitter (11) has a sensor module (35), and analog circuits (23) which provide an output representative of a sensed process variable, such as pressure, to a two-wire current loop (14). At least portions of the analog circuit (23) are removed and replaced with apparatus including a digital converter (52) that digitally calculates the transmitter output using the same current range in the current loop (14) and calculating corrections for obtaining linearity of the output.

Description

[Detailed description of the invention] name of invention Digital converter for improving the output of two-wire transmitters Background of the invention 1. Field of invention The present invention provides a method for improving the output of two-wire transmitters for sensing process variables. The present invention relates to a digital conversion device.

Summary of the invention Existing analog 2-wire transmitters combine and detect process variables. and a sensor module that generates a sensor output as a function of the process variable. Equipped with joule means. The existing transmitter also has a sensor module in hand Excitation means coupled to and exciting the stage is provided. Existing transmitters are The sensor signal is then connected to a two-wire transmitter output representing the sensed process variable. It also includes analog detection means for analog conversion.

Existing transmitters are modified to improve transmitter output . The analog detection means are removed from the transmitter and the output of the transmitter is decoded. A digitally calculating permutation device is located within the transmitter. The replacement device is Receives sensor output and performs linearity and other corrections on the output.

In a preferred embodiment, the existing excitation means are removed and the device a displacement excitation disposed within the sensor and coupled to the sensor module means to excite the same; Consists of means.

In a more preferred embodiment, this sensor module is coupled to the output of the hand sensor. rectifying means to rectify this, and analog compensation to apply analog correction to the sensor. Equipped with proper means.

In an even more preferred embodiment, the device includes output correction, span and zero adjustment. Equipped with a microprocessor that calculates the integer.

Therefore, while the existing transmitter has an improved output, this transmitter The smitter remains intact and connected to the process variable and loop. This way You can easily replace existing sensor modules or add transmitters to your process line. The output can be digitally corrected without having to disconnect or disconnect from the 2-wire loop. A transmitter is obtained.

Brief description of the drawing Figure 1 shows the upper housing and part of a conventional analog transmitter with parts removed. FIG. 4 is a sectional view of the lower housing.

FIG. 2 shows the upper and lower housing parts of a transmitter according to the present invention with a portion removed. FIG. 3 is a cross-sectional view of the housing.

FIG. 3 is a block diagram of a first preferred embodiment of the transmitter of the present invention.

FIG. 4 is a block diagram of a second preferred embodiment of the transmitter of the present invention.

5A, 5B and 5C are schematic circuit diagrams of the transmitter of the present invention. Ru.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a prior art process variable transmitter 10 connected to a flange adapter. ・It is shown bolted to the union, and its flange adapter The adapter union couples the fluid to the transmitter 10.

The transmitter 10 detects the fluid pressure at the flange φ adapter union. and provides an output current to the two-wire loop representative of the sensed pressure. Transmi The transmitter 10 is powered by an external power supply 14A coupled to a 2-wire loop and is powered by a 4-wire loop. An output current signal, such as 20 milliamps, is similarly coupled to the two-wire loop 14. is supplied to the external load 14B.

The transmitter 10 has three compartments 1 which are isolated and sealed from each other. 8. Consists of a housing 16 with 22 and 24. Transmitter 10 Also, the pressure sensor is located within the compartment 18 to control process variables such as differential pressure, gauge pressure, and absolute pressure. It has a capacitive pressure sensor 26 for sensing.

Sensor 26 is electrically connected to circuit board assembly 28 within compartment 18 via electrical leads. This circuit board assembly includes a diode or rectifier 30 that rectifies the sensor output. and an analog correction section 32 that corrects the sensor output. This correction It also includes compensation.

Cable 34 passes through a seal 36 between compartments 18 and 22 and connects to circuit board 28. is electrically connected to a connector plate 38 in the compartment 22. The connector plate 38 It consists of an additional analog correction or compensation circuit that corrects the temperature characteristics of the sensor 26. It will be done. Connector plate 38 has a multi-bin connector 42 for connecting to other transmitter circuits. It is paired with

In operation, sensor 26, circuit board assembly 28, cable 34 and connector board 38 together configure the sensor module 35 within the transmitter 10 to Detects a variable and provides a sensor output to a connector 42 that includes an analog temperature correction section .

Terminal strip 44 in sealed compartment 24 is connected to two-wire loop 14 in conduit 14C; It constitutes an airtight through-power feeding section 46 that connects a two-wire circuit from the compartment 24 to the compartment 22. Ru. A compartment 22 within the housing 16 contains an analog converter and excitation circuit assembly 2. It is said to have a shape that can accommodate 3. The excitation circuit assembly 23 excites the sensor. or convert the sensor signal into an output of 4 to 20 milliamps. Circuit assembly 23 utilizes an analog converter and an analog converter coupled to connector 42. and a printed circuit board 23A consisting of excitation electronics and a spacing coupled to the circuit board 23A. It is composed of a printed circuit board 23B consisting of a control circuit and a zero point adjustment circuit.

A pair of sealed adjustment screws 50 are inserted into the transmitter housing from inside the compartment 22. It extends to the outside of the ring 16. Adjustment screw 50 adjusts the span and width on circuit board 23B. It is used to adjust the potentiometers 23C and 23D for zero and zero points.

Analog converters are a reliable, low-cost means of output, with span and zero settings. The determination is made using potentiometers 23C and 23D. Potentiometer 23 Mechanical adjustment of C, 23D is sensitive to mechanical vibrations that change the span or zero setting. exposed. Potentiometers 23C and 23D are used to set the output span and zero point. Tension meter adjustment and resolution can be adjusted to the limit.

4 to 20 milliamps of transmitter 10 as a function of sensed pressure The linearity of the output of the transmitter 10 is improved with an analog correction circuit of the transmitter 10. child For nonlinearities such as analog converters, excitation or sensor modules Although adjustment is also performed by can get.

What is the investment to assemble and install the transmitter 10 in the process plant? The transmitter 10 is removed and a higher To replace the precision transmitter, install a transmitter 10 like this All costs are losses. If the transmitter 10 is a chemical, petroleum or valve, paper When installed in a process plant such as a plant, the transmitter 10 Complete replacement would be costly and time consuming.

If the pressure line to flange adapter union 12 has a separate isolation valve, If not, loosen the bolts and remove the flange adapter from the transmitter. When removing the flange adapter union, process fluid may spill from the flange adapter union. Shut down at least part of the plant to depressurize the lines to prevent leakage. hut dovn).

If equipped with a shut-off valve, it will remain shut off while the transmitter is being replaced. There's no need to. Loosen the bolts and remove the flange adapter from transmitter 10. The union must be removed and re-bolted to the replacement transmitter. .

Leaks when bolting flange adapter union to alternate transmitter Check the seal (tightness) between the flange, adapter, and union. must be inspected.

After replacing the transmitter 10, the replacement transmitter will lose its pressure range during the replacement. The pressure line must be vented to remove any air that may have entered the There are many bad things. To replace all transmitters 10, transmitter 1 disconnect loop 14 from terminal 44 in 0 and disconnect conduit 14 from transmitter 10. It is necessary to separate C. The replacement transmitter is then connected to loop 14 and conduit 14. It is necessary to recombine to C.

In some cases, shutting down part of the process plant to replace the transmitter It is impractical to do so, and replacing the transmitter 10 is a It may be postponed until the end of the term. Combined with flange adapter union 12 Process pipes and conduit 14C may be damaged due to aging, corrosion, vibration, etc. Do not manipulate these lines while replacing everything, as they may be weakened by If you do so, there is a risk of damaging that part.

Rather than replacing the entire transmitter, the analog voltage inside the transmitter 10 If you want to upgrade the child device by replacing it with a digital converter, replace everything. You can avoid wasting money and time. Using a digital converter for replacement The process itself, the pressure line leading to the transmitter, and the flange adapter union 12, loop wire (wiring) 14, terminal strip 44 and conduit 14 This makes it possible to prevent adverse effects and failures on C and the like.

Additionally, digital transducers allow for electrical span and zero adjustments to reduce vibration This eliminates the need for sensitive potentiometers. span and zero Higher resolution than that of the potentiometer is achieved by electrical adjustment of the points, More accurate span and zero point settings are possible.

Digital converters also provide a wider range and more linear transmitter output. Realizes digital linearity correction that provides power. Including housing and temperature compensation section Transmitters such as sensor modules, terminal strips and connections to loops, etc. The main parts of the transmitter 10 are suitable for use with digital circuits and are The performance of the system is improved by this high precision system. .

As a result, analog converter 23A can be removed from transmitter 10. By incorporating equipment with a digital converter, the transmitter 10 can be It can be improved to any desired level. Transmission by digital converter Upgrading the converter requires the original equipment, assembly effort, and analog compensator. The effort and equipment spent on incorporating it into the process line will be wasted. enable prevention. Span, zero, and other adjustments to digital converters Adjustment is done without the use of potentiometers, providing a high degree of stability and ease of setting. can get.

FIG. 2 shows a typical transmitter 11 having such a digital converter. It is shown. In Figure 2, reference numbers indicate identical parts of corresponding features. To show this, it is the same as the one in Figure 1. In Figure 2, the digital Transducer 52 is incorporated within transmitter 11 and assembly 23 (shown in FIG. ) have been previously removed from the transmitter 11.

Transmitter 11 thus has an output to loop 14, which loop itself Maintains improved accuracy by simply interfacing with control systems via the body are doing. The digital converter 52 is an analog Because it performs a second compensation or correction in addition to the has been improved to the desired level, while replacing all transmitters. It saves you the time, expense and inconvenience of having to

Instrument 52 is mounted within chamber 22 of transmitter 11 and is is sealed inside the transmitter. The circuits of device 52 accumulate energy. The transmitter's inherent safety features are Retained.

FIG. 3 shows a first embodiment of a transmitter 500 manufactured according to the present invention. It is shown.

Transmitter 500 is coupled to the process variable through line 514. La The process variables for IN514.1 are absolute pressure, gauge pressure or differential pressure, temperature, PH , flow rate, conductivity, etc. Transmitter 500 is on line 514 The above process variables are sensed to generate a function of the process variables and an output at 15.

Transmitter 500 further connects a two-wire route through conductors 503 and 505, respectively. It has output terminals 502 and 504 connected to a terminal 506. The power supply 508 is the conductor 503 and conductor 507 in series with loop 506 to supply energy to transmitter 500. supplying Rugy. Transmitter 500 is connected to an output terminal by conductor 502. 502 and is also connected to output terminal 50 by conductor 540 through resistor 542. 4 is provided.

Current control 536 controls the current in loop 506 as a function of the sensed process variable. Control the flow I. Therefore, the current I is the output of the transmitter. Current 1 is A low frequency electric current of 4 to 20 milliamps that is linearly proportional to the sensed process variable. It is preferable that the flow is smooth. The current control section 536 also controls the current generated across the resistor 542. is connected to the output terminal 504 by a conductor 544 to detect the voltage It is preferable.

This voltage is representative of the loop current I.

The current control unit 536 monitors the loop current in this manner and controls the loop current I. control in a closed loop. A resistor 510 is connected between conductors 505 and 507 in loop 506. Continued.

Loop current I flows through resistor 510. Utilization equipment device) 512 uses the voltage generated across the resistor 510 control computer, loop controller, chart recorder, instrument etc. It may consist of other display, recording or control equipment.

The current control unit 536 has a first communication output (communicationoutp). ut). The first communication output is a high frequency, frequency shift keyed (FS) K: frequency-shift-keyed) continuous signal. is preferable. Keying or modulation frequency of the first communication output The number is such that the first communication output does not substantially interfere with the operation of the utilization device 512. , away from the low frequency of the loop current l so that it can be superimposed on the loop current l.

It is preferable that the

The first communication output is the span and zero settings, the transmitter (sequential) number, and the detection transmitter, such as the identification code of the process variable, the current intensity of the process variable, etc. Contains data or installation parameters describing the operation of the system. The first communication output is , from the current control unit 536 to the output terminals 502, 504 via conductors 520, 540. conductors 503 and 505 of loops 506, respectively. It is connected to the.

Communication means 516 connects with conductors 503 and 505 through conductors 546 and 548, respectively. It continues. The communication means 516 connects conductors 520, 503, 5 from the current control section 536. A first communication output is received through 46, 505 and 540. therefore communication Means 516 receives data contained in the first communication output and transmits the data from the transmitter. Give the data to a user in a remote location. The communication means 516 preferably is capacitively coupled to the loop 506, and the low frequency loop current l flows through the communication means 516. It doesn't flow through.

In the embodiment described in connection with FIG. However, as is clear to those skilled in the art, such communication signals are transformer via a conductor (line) or bus that is separated from the loop. It can also be AC coupled to a transmitter.

The transmitter 10 further receives a portion of the loop current and transmits a controlled energy. is connected to conductor 520 to energize the transmitter circuit at a voltage level. It has a regulator 518. Regulator 518 connects power to conductor 522. is supplied to the excitation means 526 through the conductor 524 and to the calculation means 532 through the conductor 524. do. The portion of the loop current coupled to regulator 518 is and a conducting wire 550 that connects between the conducting wire 540 and the conducting wire 540, and It is returned to the loop through a connecting conductor 552.

Excitation means 526 is an excitation means coupled to sensor module 528 by conductor 527. Generate output. Sensor modules are used to detect process variables. 514 to process variables. The excitation output on lead 527 is from the sensor monitor. Excite Joule 528. Sensor module 528 detects detected process changes. The sensor output, which is a function of quantity, is transmitted through conductor 530. Sensor module 5 28 further includes an analog circuit 529 that corrects the sensor output on conductor 530. .

The correction applied by analog circuitry 529 is based on the sensitivity of the sensed parameter. This is to correct the deviation of the sensor output from the desired response. analog circuit 5 The correction applied by 29 is the linearity of the sensor output as a function of the process variable. compensation, temperature compensation for sensor output representing pressure, flow rate, and conductivity, and cooling compensation for thermocouples. This may include bond compensation and the like. In a preferred embodiment, sensor module 528 further includes: , a rectifying means for rectifying the sensor output on the conducting wire 530 is provided.

The sensor output on lead 530 is coupled to computing means 532 .

The calculation means 532 calculates the calculation output as a function of the sensor output. The calculation output is is indicative of a desired output, such as the amplitude of current I in loop 506, and is representative of the sensed output. It is also a function of the given parameters.

Constant 533 is stored inside the calculation means. Constant 533 is the transmitter output It represents the digital correction of the correction made by the analog circuit 529. In addition to further improving the transmitter output. Constant 533 is linearity correction, Perform span correction, zero correction, or other improvements to the transmitter's output characteristics. may include corrections. In the preferred embodiment, constant 533 is the linearity, span and composite (a+ult1ple) correction of zero point setting.

The calculation output is coupled to a current controller 536 through a conductor 534. preferred practice In the example, the current control unit 536 transfers the calculation output on the conductor 534 to the conductor 544. Compared to the sensed sense current, i.e. the actual current I, the actual current l is so that it is substantially equal to the calculated current I expressed by the calculation output on 34. , controls the current on conductor 520.

The transmitter output is thus subject to both analog and digital correction. It has been improved from the front. Since the equipment used has been digitally corrected, it has been detected that better representative of the parameters.

In a preferred embodiment, the computing means 532 is also connected via conductor 534 (computing means 532 (along with the output) also generates an output representing a first communication output coupled to the current control section 536. do. Therefore, the current control unit 536 converts the current that is the first communication output into a loop current. superimpose it on

In a more preferred embodiment, the communication means 516 represents the correction constants from the user. Receive the data. The communication means 516 communicates from the correction constant on the conductors 546, 548. second communication outputs are coupled to conductors 503 and 505, respectively. Transmit In the terminal 500, the second communication output is passed through the resistor 542 from the terminals 502 and 504. , are coupled to computing means 532 via conductors 524 and 552.

The calculation means 532 receives the second communication output and converts the data contained therein into a constant 533. be memorized as . Transmitter 500 can thus transmit correction constants from a remote location. 533 can be given. In order to adjust the correction constant 533, the transformer There is no need to locate or open the emitter 500. Figure 3 The transmitter 500 shown in FIG. 528, calculation means 532, current control section 536, regulator 518 and resistor 542 permutation converter is used. Displacement excitation means 526 are also provided. It will be done.

FIG. 4 shows a two-wire, 4 to 20 milliampere circuit connected to loop 14. A block diagram of a second preferred embodiment of the circuit of transmitter 10 is shown. . Transmitter 10 is coupled to the loop at its terminals 60,62.

An energizing source 64, such as a battery or power supply, is connected to a loop load represented by a resistor 66A. They are coupled in series through conductive wire 15.

The loop load can be for example from a control computer, chart recorder or ammeter. Become. Loop current flows from energizing source 64 through conductor 64A to a transformer at terminal 60. from the transmitter through conductor 62A from terminal 62 to resistor 6. 6A, thus powering the transmitter 10 from the loop. Tiger Diode 59 within transmitter 10 provides reverse polarity protection to transmitter 10 .

The amplitude of the low frequency loop current is controlled by a current control 66 coupled to terminals 60,62. controlled, so the amplitude of the loop current is sensed by the transmitter. is a function of the process variable. First regulator 68 is connected to terminal 60 and applies a first regulated voltage on conductor 70 in transmitter 10 . No. A second regulator 72 connects to conductor 70 and applies a second regulated voltage to conductor 74. Apply.

The current flowing through the transmitter returns to the common conductor 76 in the transmitter 10, The conductor is connected to terminal 62 through resistor 78 . The electric current generated across the resistor 78 voltage represents the actual loop current, and this voltage is passed through conductor 80 to the digital analog is fed back to the converter (DAC) 82 for closed-loop control of the transmitter output current. used. The excitation means 84 is energized via conductors 70° 74 and is energized through conductors 86. to excite the sensor module 88. Sensor module 88 is a capacitive pressure sensor , an analog linearity and temperature compensation element and a rectifier circuit. can.

The sensor module 88 transmits the sensor output as a function of the sensed parameter to the conductor 90. is coupled to integrator 92 by.

Temperature compensation using analog techniques is done inside the sensor module 88. in The interface circuit 94 is connected to the integrator 92 through conductors 91.93 and is connected to the integrator circuit. interface between circuit 92 and integrator timer 96 and microcomputer 98. conduct a course.

Integrator 92 is powered by leads 70 and 76 and is connected to a tie which is powered by leads 74 and 76. It operates at a higher voltage than the microcomputer 96 and the microcomputer 98. This voltage difference For this reason, the interface circuit provides level shifting to achieve a harmonious signal level. ensure that the Integrator 92, interface circuit 94 and integrator timer 96 operates in conjunction with a microcomputer 98 to provide a double slope type analog digital A digital converter 99 is formed.

Dual slope transducer 99 receives the corrected analog signal from sensor module 88. Performs analog/digital conversion of sensor output. The double slope converter 99 is In this way, a digital signal representative of the temperature-compensated sensor output is sent to the microcomputer. Send to computer98. The microcomputer 98 has a microphone on one integrated circuit. processor, program memory and random access memory, 1-chip microcomputer with favorable low power consumption and compact size It is preferable that

In other embodiments, the microcomputer 98 may have space and power specifications as designed. If compatible, it should be constructed from separate microprocessors, program ROM, and RAM. It can also be done.

In one preferred embodiment, “watchdog 1 timer 102 is The microcomputer 98 is connected to the computer 98, and the microcomputer 98 controls the watchdog timer. - When the selected task fails to execute within the time limit set in 102, this Detect. Failure to execute a task within the time limit is due to an error in the microcomputer 98. behavior and the watchdog timer will trigger a micro-clock when such a failure occurs. Reset your computer. Nonvolatile connected to microcomputer 98 Memory 104 is loaded with constants representing the transmitter's digital linearity correction. has been coded.

Therefore, the improved transmitter is Sometimes, in addition to the analog correction section provided inside the sensor module 88, A digital correction section for the emitter output can be provided. microcomputer The controller 98 performs a transform based on the digital correction word stored in the memory 104. Calculate the transmitter output. The obtained calculation output is the original analog transmitter output. The accuracy is improved to exceed the accuracy of force. Calculated transmitter output is connected to a digital-to-analog converter (DAC) 82 through conductor 106. Ru.

DAC 82 compares the calculated output with the signal on lead 80 representing the actual loop current. do. DAC 82 couples the signal to current control 66 through conductor 108 and loops so that the current in is equal to the desired calculated transmitter output. My A communication circuit 112 coupled to a computer 98 provides correction for the transmitter. Provides a means to receive digital words such as constants, spans and zero settings from the loop. There is.

The communication circuitry 112 within the transmitter is part of a digital control system or or a second communication circuit, which may be a separate device that couples to the loop at a remote location. 114 to form a two-way communication circuit. A, connected by 64A. Data representing span, zero and linearity corrections are The signal is taken into the second communication circuit 114.

The second communication circuit 114 is connected to the loop conductors 62A, 64A and within the transmitter. The high frequency signal is connected to the communication circuit 112 via the conductor 76.126. high frequency signal The signal is detected by communication circuitry 112 within the transmitter and a "carrier detect" signal is sent from the communication circuit 112 to the microcomputer 98 via the conductor 116. . When the carrier detection signal is detected, the microcomputer 98 A signal is sent to communication circuit 112.

The communication circuit 112 closes the switch 122 to connect the modem 124 in the communication circuit 112. Supply power. The modem 124 is connected through conductors 126.128.76.62A, 64A. and performs bidirectional communication with the second communication circuit 114. The correction constant is determined by modem 124. The data is received by the microcomputer 98 and transferred to the memory 104. vinegar Pan and zero constants are similarly received and stored in memory 104.

Modem 124 controls transmitter functions stored in memory 104. Data indicating the status of constants, including controlled parameters, sequence numbers, and maintenance history. Similarly to data representing process variables, it is transmitted to a second communication circuit.

The combined energizing current supplied to the circuit is 4 milliamps of energizing current which can be taken from the loop. It may exceed the level. The excitation circuit 84 and the microcomputer 98 are the same. in series so that the same current flows through both, effectively controlling the total energizing current from the loop. connected to. Charge pump 132 further reduces the excitation current at the loop terminals. between conductors 70, 74 and 76 to reduce the charge pump is , so that the current requirements of two series connected energizing circuits are better balanced. , transfers charge between series connected loads. This is true at the transmitter terminal. further reduce the energizing current.

During normal transmitter operation, switch 122 is open and the mode Since the operation of the system is stopped, the required amount of energization is further reduced. Transmit from loop The energizing current to the generator is thus kept below 4 milliamps. Therefore, The transmitter can be operated with a loop 14 of 4 to 20 milliamps. It is Noh. However, during communication between modem 124 and circuit 114, the excitation current consumption is It may temporarily exceed 4 milliamps.

A first portion of the transmitter circuit is shown in FIG. 5A. sensor moji The capacitor 88 is shown within the dotted box and is connected through the fixed capacitors 142 and 144. It consists of a capacitive pressure sensor connected to an array of rectifying diodes 146.

The rectifier diode 146 is connected to the excitation circuit 84, and the excitation circuit is connected to the rectifier diode. Capacitive pressure sensor 140 is energized through port 146 .

Sensor module 88 further includes selected fixed resistors 148, 150, 152, 154, 156, 158 and thermistors 162, 164. thermistor 162 and 164 are coupled to sensor 140 and fixed capacitors 142 and 144. This is a compensation element that provides analog temperature compensation to the sensor 140. sensor module The circuit 88 also includes a correction capacitor 166, which was used in the previous analog converter. However, it does not need to be connected to the digital converter and is not used.

Excitation means 84 includes resistors 168, 170, 172, 174°176, 178. Conde Sensors 180, 182, 184. .

186.188,190,192. Amplifier 194, 196° transistor 198 and a transformer with five windings coupled together for excitation. Ru. The operation of the excitation circuit in cooperation with the sensor module was described by Roger L. Frick (ROger L, Pr1ck) U.S. Pat. No. 3,646.538. Yes Sensor module 88 sends a sensor current "Is" representative of the sensed pressure to conductor 2. 02 to the integrating circuit 92. Sensor module 88 also provides analog temperature A compensation current "It" is sent to the integrating circuit 92 through conductor 204. Sensor current “ Is” and the analog temperature compensation current “It” are connected to the amplifier 208 and the resistors 210 and 212. , 214, 216 and a capacitor 218 at node 206. be done.

The amplification stage represents the sum of the current (1s+It) and therefore the sensor module's current A voltage is generated on conductor 218 representing the sensor output corrected by the analog compensation circuit. . The conductor 218 passes through a switch (field effect transistor, FET) 220 to It is connected to dividing stage 222 . A virtually fixed reference potential on conductor 224 is connected to the switch ( FET) 22B to the integrating stage 222. Integrating stage 222 is mutually Amplifier 228. connected as shown in Figure 5A. capacitor 230 and resistor It is composed of 232. Switches 220 and 226 are alternately energized. Then, the integrating stage 228 integrates the sensor potential and the fixed potential alternately.

Integrating stage 222 integrates the voltage applied by switches 220 and 226 over time. output on conductor 234. The output of the integrating stage is passed through lead 234 to comparator 236. The integrator output is compared to a substantially fixed voltage on lead 238.

The output of the comparator is sent on lead 240 and transmitted to the circuit of FIG. 5B, described below. .

A second regulator 72, which is part of the power supply circuit, is connected between conductors 70 and 74. Reference is made to the excitation circuit, integration circuit, and temperature compensation circuit in the sensor module 88 (standard ) generates an intermediate supply voltage on voltage supply conductors 224 and 238; second legi The regulator includes resistors 244A, 246 coupled together as shown in FIG. 5A. , 248, 250, 252. adjustable reference nce) 254 and capacitors 256 and 258.

The connector labeled “J2” in Figure 5A is labeled “J2°” in Figure 5B. Connected to the connector shown.

In FIG. 5B, NAND gates 246 and 248 are coupled together to A top circuit 250 is configured. The comparator output (Figure 5A) is connected from lead 240 to the The set of flip-flops 250 is sent out through the connector J2. . The first output Q of flip-flop 250 is routed from conductor 244 through connector J2. It is connected to the gate input of switch 226 (Figure 5A). flip flop 2 A second output Q of 50 is passed from conductor 242 through connector J2 to switch 220 (fifth It is connected to the gate input in Figure A).

The excitation voltage passes through connector J2 and is connected through conductors 70, 74 and 76. There is. Timer 96 connects the low level timer output on conductor 252 to inverter 25. 6 to a level shift buffer 254 which provides a high level timer output.

Timer 96 is manufactured by RCA Corporation, part number CD4536B. It is preferable to consist of the following.

Inverter 256 connects the high level timer output to the flip-flop through conductor 258. to the reset input of step 250.

The Q output of flip-flop 250 passes through buffer y260 to the reset of timer 96. Supplied to set input. The Q output of the flip-flop 250 is connected to the inverter 26 2 and is supplied to the input of the microcomputer 98. microcomputer 98 is part number 80C59 manufactured by Oki Semiconductor Company. is preferable.

Microcomputer 98 sends a clock signal to timer 96 through conductor 264. supply Flip-flop 250, timer 96 and integrator circuit 92 together Therefore, it functions as a double slope integrator circuit. Q output of flip-flop 250 has a pulse width representing the composite current (Is+It).

Therefore, the signal coupled to the microcomputer 98 is transmitted to the sensor module 88. represents the sensed parameters, including any analog corrections applied within the system.

The microcomputer 98 is an analog/digital sensor output (Is + It) During this pulse width from inverter 262, the self Count clock pulses.

The watchdog timers 102 are coupled together as shown in FIG. 5B. Inverters 268, 270. Capacitors 272, 274, 276, resistors 278 , 280. ) consists of a transistor 282 and a diode 284.

During normal operation of the microcomputer 98, the microcomputer 98 periodically Wire 290 provides a pulse to watchdog timer 102 . Conductor 29 A pulse above 0 resets watchdog timer 102 and is output on lead 292. Prevents the generation of force.

However, the microcomputer 98 malfunctions and the watchdog timer If you fail to send a pulse to conductor 290 at the set time interval, A watchdog timer output is issued on line 292 to microcomputer 9. 8 and normal operation begins again. The determined time interval is the resistance 2 80,278 and the capacitance of capacitors 214,218.

Electrically erasable read only memory (EEROM) 104 is a microcomputer 98, span, zero, etc., as described in connection with FIG. Stores digital recognition representing physical corrections. The microprocessor is in memory 104 The stored correction constant is read and the output correction amount is calculated as a function of the constant.

The crystal 292 is combined with the microcomputer 98 to create a stable clock. or provide reference time.

The operation of the transmitter is described as having a separate non-volatile memory 104. However, a person skilled in the art knows that part of the RAM in the microcomputer 98 is , may be powered by a battery to non-volatilely store correction constants etc. will be understood. Conductors 70, 74 and 76 are level shifters (buffers) 254 to energize it.

The connector labeled 'J3' in Figure 5B is the connector from the microcomputer 98. Connect the conductors to the circuit shown in Figure 5C. Power supply lines 70, 74, 76 are also It is connected through connector "J3" to the circuit shown in FIG. 5C.

The connector labeled “J3°” in Figure 5C is labeled “J3” in Figure 5B. and the power supply 70.74.76 connects to connector “J3”. through which it is connected to the circuit shown in Figure 5B.

The transmitter connects the loop 14 through the terminal 60.62'i shown in FIG. 5C. connected to. Current from loop 14 flows into the transmitter from terminal 60. . Terminal 60 is connected to conductor 126 through polarity protection diode 59. instrument end Children 61 and 63 are used to connect appropriate display instruments 65 in wiring compartment 24 (FIG. 2). diode 59.

A first regulator 68 receives an energized portion of the loop current from conductor 126. It is connected to a conductor 326 for use.

The first regulator 68 includes resistors 3 coupled together as shown in FIG. 5C. 00,302,304,306°308.310,312. capacitor 314, 316°318, amplifier 320. Transistors 322, 324. diode 32 Consists of 6,328 and Zener diode 330°332,334,336 and generates a regulated voltage. Regulator 68 connects conductor 70 to a first Supply rectified voltage.

Current control circuit 66 connects conductor 126 and terminal 62 to control the amount of current in the loop. connected between. Current control circuit 66 controls the flow of current from conductor 126 to terminal 62. Amplifiers 350° coupled together as shown in FIG. 5C to control Resistors 78, 352, 354, 356. Transistor 358°360 capacitor 362 and Zener diodes 364° and 366. The amplifier is Transistor 3 receiving a control input on conductor 368 and wired in a Darlington structure At 58.360, a current is delivered through resistor 354.

A portion of the loop current flows from conductor 126 to Zener diode 364 to transistor 3. 58.360 and flows through resistor 356 to conductor 76. Is it a transmitter circuit? Current from the remaining portions flows into conductor 76, which is the common conductor of the circuit.

In this way, substantially all of the loop current flows from conductor 76 through resistor 78 to terminal 62 and returns to the loop. The voltage generated across resistor 78 connects conductor 370. is led to the DAC82.

The DAC82 is manufactured by Analog Devices, part number AD7543. I would like it to be done. DAC 82 connects the voltage on conductor 370 to The calculation output signal received from 372 is compared. Busbar 372 connects from the DAC. Connected to microcomputer 98 (shown in Figure 5B) through data center J3. be done.

Communication circuit 112 receives a first communication signal as described in connection with FIG. The communication output is sent to the current controller via conductor 128 for supplying the loop. Second The communication output of is connected to communication circuit 112 through conductor 126 from the loop at terminal 60. connected to. Communication circuit 112 receives a second communication signal from conductor 126 and demodulates the communication signal. The demodulated second communication signal is sent to the connection via bus 374. The signal is connected to the microcomputer 98 (FIG. 5B) through the terminal J3. communication circuit 112 includes a filter 376 that filters and amplifies the communication signal received from the loop. have

Filter 376 includes a detection circuit 378 that detects the presence of a carrier wave and a communication signal. It is connected to a modem 124 for modulation and demodulation. Modem 124 is Texas Instruments Part number TCM3105 manufactured by Ment Corporation is preferred. carrier wave detector 378 is connected to the microcomputer 98 (No. 3) from the conductor 116 through the connector J3. (Figure 5B). When the carrier wave is detected, the microcomputer 98 A signal is sent through conductor 118 to switch 122 which energizes modem 124. .

Charge pump 132 is connected between conductors 70, 74 and 76. charge The pump has a capacitor 390 coupled to a charge pump integrated circuit 392. It is preferable that The charge pump integrated circuit 392 is manufactured by Intensil Corporation. Part number 7660 is preferred. Capacitor 390 is from conductor 70.74 It is charged and then discharged into conductors 74, 76 so that the currents are balanced.

The device is thus designed with the transmitter installed in place in the process plant. can be configured to apply any desired digital corrections to its output.

In order to perform digital linearity correction, the digitally calculated output must be acquired. However, it is possible to eliminate the cost of replacing the entire transmitter. Trance The mitter is compatible with the device of the invention while it remains in place in the process equipment. Is possible.

Although the embodiment described here is supposed to have a linear output, For those skilled in the art, the present invention can be applied to non-linear outputs such as square root outputs, and reverse operation outputs (re Verse acting output) can be used as well. That will be understood.

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Claims (11)

[Claims] 1. electrically connected to its first and second terminals from its internal transmitting circuit; The ability to send output information through a two-wire current carrying loop adapted to Adds the ability to receive input information to the built-in parameter value transmitter. , wherein the output information is of a structure in which the transmitter is installed. Parameters that are state dependent and measured by sensing means in the transmitter In a method of adding an input information receiving capability, such as formed based on the value of between the sensing means of the transmitter mounted on the structure and the first and second terminals; by opening at least a portion of the transmitting circuit set that is originally electrically connected to the removing stage, and a sensing means and first and second terminals within the transmitter mounted on the structure; This process consists of installing and modifying a transmitter/receiver circuit set that is electrically connected between The transmitting and receiving circuit of the transmitter modified in this way transmits the output information and 1. A method having a function of being able to receive one input information. 2. In the method according to claim 1, the modified transmitter the transmission of the output information using a transmission signal having frequency components within the first frequency range; reception of input information by the modified transmitter at a first frequency. using a received signal having frequency components in a second frequency domain separated from the the way it is done. 3. In the method according to claim 1, the detection means includes a sensor and a sensor. It consists of an output signal correction circuit, and the sensor and the sensor output correction circuit are space within the transmitter that was in place before the signal circuit set was removed. isolated from the space within the modified transmitter containing the The way it is sealed. 4. In the method according to claim 1, the input information includes span and zero adjustment. A method that is a separate representation. 5. electrically from a first set of transmitter circuits therein to its first and second terminals; transmitting the first information through a two-wire current carrying loop adapted to be connected to the A selected second parameter value transmitter that is initially capable of transmitting A method for adding the ability to transmit information, the first information being a transmitter. depending on the condition of the structure to which the transmitter is installed and the sensing means within the transmitter. The selected index is formed based on the value of the parameter measured by In the second method of adding information transmission capability, a transmitter attached to a structure electrically connected from the beginning between the detection means of the terminal and the first and second terminals. opening and removing at least a portion of the first set of transmitter circuits; and a sensing means and first and second terminals within the transmitter mounted on the structure; The process consists of the step of installing and modifying a second transmitting circuit set that is electrically connected between , this second transmitting circuit is configured such that the thus modified transmitter is connected to the first and second transmitter circuits. Has the ability to allow both output information to be sent via a two-wire loop. The way things are. 6. In the method according to claim 5, the modified transmitter the transmission of the first information using a transmission signal having frequency components within the first frequency range; transmission of the second information by the modified transmitter Using a transmitted signal having frequency components in a second frequency domain separated from the frequency domain. A method carried out using 7. first and second terminals within the transmitter and receiving an input information signal; within the transmitter through a two-wire loop adapted to be electrically connected to the a transmitting/receiving circuit for transmitting the value of the parameter measured by the detecting means; Parameter values depend on the state of the structure to which the transmitter is installed A parameter value transmitter, such as first and second terminal means electrically connected to the first and second terminals, respectively; and a transmitting/receiving circuit, The transmitting/receiving means includes: first and second voltage values to be applied to the first and second terminal means; and a third voltage value intermediate the first and second voltage values to be applied to the stage. Different voltage values can be supplied to said three terminal means, and between said first and third terminal means A second circuit that is capable of passing a greater total current than the transmitting and receiving circuit parts electrically connected to the a power supply in which there is a transmitting/receiving circuit part electrically connected between the second and third terminal means; and a pair of terminals, and one selected terminal of the charge storage means is a first terminal. alternately electrically between the first and third terminal means; connected, and then the opposite terminal of the charge storage means is connected to the third terminal means. a charge storage means that can be electrically connected between the second and third terminals; A parameter value transmitter with. 8. An apparatus according to claim 7, wherein the first terminal means is a voltage regulating circuit. and a second terminal means electrically connected to the first terminal through the current sensing resistor. electrically connected to the second terminal. 9. 7. The apparatus according to claim 7, wherein the transmitting/receiving circuit comprises a first and a second transmitting/receiving circuit. A terminal that receives information signals. 10. 7. The device according to claim 7, wherein the power supply means is connected to the first and second one that can be operated by a current supplied at the terminals of 2; 11. Adapted to be electrically connected to the first and second terminals within the transmitter The parameter value is transmitted through a two-wire loop connected to the transmitter installation. by sensing means within the transmitter, depending on the condition of the structure being A parameter value transducer with a transmitter/receiver circuit that transmits parameter values measured by a transmitter, at first and second terminals of the transmitter; Microwave in the transmitter/receiver circuit installed in the transmitter that controls signal transmission a processor; The microprogram is configured to send the value of the parameter within the time set by the reset timer. The microprocessor associated with this transmission when the processor fails to command A function is provided within the transmitter that allows the operating sequence within the transmitter to be reset. A reset timer means in the transmitter/receiver circuit and a parameter value transmitter.