CN102538904A - HART (Highway Addressable Remote Transducer)-communication-based capacitive level transmitter and working method thereof - Google Patents
HART (Highway Addressable Remote Transducer)-communication-based capacitive level transmitter and working method thereof Download PDFInfo
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- CN102538904A CN102538904A CN2010105786690A CN201010578669A CN102538904A CN 102538904 A CN102538904 A CN 102538904A CN 2010105786690 A CN2010105786690 A CN 2010105786690A CN 201010578669 A CN201010578669 A CN 201010578669A CN 102538904 A CN102538904 A CN 102538904A
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Abstract
The invention relates to a HART (Highway Addressable Remote Transducer)-communication-based capacitive level transmitter and a working method thereof. The HART-communication-based capacitive level transmitter is characterized in that: a digital communication function is additionally provided based on a two-wire system capacitive level transmitter, digital signals and analog signals can be simultaneously transmitted without disturbing each other by adopting the standard of Bell202FSK (Bell202 Frequency Shift Key) signals, therefore, the both-way communication is achieved; meanwhile, the measuring accuracy and the utilization ratio of the capacitive level transmitter are improved, the HART-communication-based capacitive level transmitter is convenient in mounting, adjustment, maintenance and control, and the cost for control is lowered, so that the role of the HART-communication-based capacitive level transmitter in the fields of detection and control is greatly enhanced.
Description
Technical field
The present invention relates to a kind of detection technique, particularly a kind of capacitance object position transmitter based on the HART communication.
Background technology
The thing position is meant the interface location between liquid in the hold-up vessel or the equipment of industrial product, pulverulent solids, the gas, also can be owing to density does not wait the interface location that forms between mutual exclusive two kinds of liquid.Be divided into liquid level, material level, boundary's level sensor or transmitter according to concrete purposes.The thing position is one of major parameter related in the control procedure.The parameter of material consumption or output metering is not only in the thing position, also is the important parameter that guarantees production continuously and device security.Particularly in the modern chemical industry industry, production scale is big, and speed is high, and high temperature, high pressure, severe corrosive or inflammable and explosive material are often arranged, and is most important especially with automatic control for the supervision of thing position.Therefore, account for critical role in the process control of thing position detection technique modern chemical industry industry.Level transmitter in the power station, industrial circle such as petrochemical industry, oil field is widely used.Through measurement to the thing position; Obtain the continuous variable or the switching value signal of thing position; To obtain the quantity of material in the container; So that regulate the inflow and outflow flow of material, thereby realize processing and the optimized control of process, and useful information is provided storage management at line material to material.
Capacitance type sensor is a kind of sensor that the variation of tested non electrical quantity is converted into electric capacitance change.Though capacitance type sensor is subject to the influence of distributed capacitance, and antijamming capability and signal long-distance transmissions ability are not high yet.But capacitance type sensor has simple in structure, plurality of advantages such as resolution height.And can under mal-conditions such as hyperthermia radiation and judder, work.The capacitance object position transmitter is applicable to that industrial enterprise measures and control production run in process of production, and is main as type conduction and the liquids position of non-conductive medium or the remote continuous coverage and the indication of powder shape solid material level.As the classic method of measurement object position, measurement by capacitance is less demanding to site environment, and simple, and is easy to maintenance, also can be applicable to many industrial occasions.The capacitance object position transmitter is product moulding the most at present, and function is the most perfect, uses the most a kind of level meter.
Along with the application of field bus technique in industrial process control field; The networking of automated system, total linearize are big trend; Original capacitance object position transmitter can not carry out digital communication through the control of 4～20mA simulating signal, can not satisfy the requirement of modern industry system.
Because the HART agreement has the characteristics of compatible with digital signal and simulating signal; Under the prerequisite that does not influence simulating signal control, can carry out digital communication; Have on-the-spot and remote parameter monitoring function, have incomparable advantage aspect reduction system cost, raising control accuracy and the system reliability.
The intelligence instrument that has the HART agreement is at present monopolized by The foreign chicken products on the market at home always; Because the monopolization of its fancy price and technology; The production cost of domestic enterprise is increased greatly; Reduced the competitiveness of enterprise, therefore researched and developed capacitance object position transmitter and have very big realistic meaning based on the HART communication with independent intellectual property right.
Summary of the invention
The present invention be directed to existing capacitance object position transmitter and can't realize the problem of digital communication; A kind of capacitance object position transmitter and method of work based on the HART communication proposed; On two-wire system capacitance object position transmitter basis, increased digital communication functions; Digital signal and simulating signal are transmitted under non-interfering situation simultaneously, realize both-way communication, strengthen its effect in the Detection & Controling field greatly.
Technical scheme of the present invention is: a kind of capacitance object position transmitter based on the HART communication; Capacitance object position transmitter based on the HART communication; Comprise with MCU being MCU control circuit unit, signal processing unit, AD conversion unit, D/A conversion unit and the HART communication interface of core; Signal processing unit is changed sensor signal, and the capacitance of measuring is adjusted to the correspondent voltage value; Magnitude of voltage is sent into the collection that AD conversion unit carries out data, and data are admitted to the MCU control circuit unit; After the MSP430 single-chip microcomputer of MCU control circuit unit obtained communication of HART communication interface or the instruction through man-machine interface, MCU control circuit unit output image data signal converted standard signal output into to D/A conversion unit; Signal processing unit comprises square-wave generator, first gating switch, BPF., voltage follower, sensor, voltage current adapter, second gating switch, phase-sensitive detector (PSD), low-pass filter successively; When sending into first gating switch, the square wave that square-wave generator sends sends into the phase-sensitive detector (PSD) of rear end; Voltage follower output signal is delivered to second gating switch through the synchronous signal of sensor, and MCU control circuit unit output signal control signal second gating switch is selected sensor signal.
Said HART communication interface mainly is made up of MCU interface and transformer coupled interface, and MCU itself has serial ports and can be used as the communication interface with HART MODEM.
A kind of method of work of the capacitance object position transmitter based on the HART communication; Comprise capacitance object position transmitter based on the HART communication; Said signal processing unit is with the simulating signal process MCU control circuit unit of sensor sample; Compare computing, carry out exporting 4～20mA simulating signal by D/A conversion unit after the data processing, realize the level gauging of capacitance object position transmitter according to sampled value; Simultaneously, HART communication interface electric circuit inspection demodulates the digital signal of stack to the external control signal that is superimposed upon on 4～20mA direct current signal, and the CPU that sends the MCU control circuit unit to handles; Process result is that the alternating signal of HART semaphore request and being superimposed upon on the direct current signal is seen off through HART communication interface circuit modulation conversion.
Said HART agreement adopts the Bell202 frequency shift keying signal of standard to communicate with 1200 baud rates, and its Physical layer adopts the sinusoidal signal of 1200Hz and two kinds of different frequencies of 2200Hz, is superimposed upon on 4～20mA signal to communicate.
Beneficial effect of the present invention is: the capacitance object position transmitter and the method for work that the present invention is based on the HART communication; Realize both-way communication; Improved simultaneously the measuring accuracy and the utilization factor of capacitance object position transmitter again, be convenient to installation, adjustment, maintenance and control, reduced and controlled cost.
Description of drawings
Fig. 1 is the capacitance object position transmitter schematic diagram that the present invention is based on the HART communication interface;
Fig. 2 is single-chip microcomputer of the present invention and HART communication interface figure.
Embodiment
Based on the capacitance object position transmitter of HART communication, comprise with MCU being MCU control circuit unit 1, signal processing unit 2, AD conversion unit 3, D/A conversion unit 4 and the HART communication interface 5 of core.MCU control circuit unit 1 comprises power module 11, MSP430 single-chip microcomputer 12 and man-machine interface; Signal processing unit 2 mainly is that sensor signal is changed, and the capacitance of measuring is adjusted to the correspondent voltage value; Magnitude of voltage is sent into A/D converting unit 3 and is carried out the collection of data, and data are admitted to MCU control circuit unit 1; After the MSP430 single-chip microcomputer 12 of MCU control circuit unit 1 obtained 5 communications of HART communication interface or the instruction through man-machine interface, MCU control circuit unit 1 output image data signal converted corresponding 4～20mA output into to D/A converting unit 4; HART communication interface 5 also comprises the modulation-demodulation circuit that is made up of special-purpose HART modem chip.Signal processing unit 2 comprises square-wave generator 21, first gating switch 22, BPF. 23, voltage follower 24, sensor 25, voltage current adapter 26, second gating switch 27, phase-sensitive detector (PSD) 28, low-pass filter 29 successively; When sending into first gating switch 22, the square wave of several different angles that square-wave generator 21 sends sends into the phase-sensitive detector (PSD) 28 of rear end; Voltage follower 24 output signals are delivered to second gating switch 27 through the synchronous signal of sensor 25, and MCU control circuit unit 1 output signal control signal second gating switch 27 is selected sensor signal.
The present invention is through being provided with HART communication interface circuit, MCU control circuit unit; The simulating signal of sensor sample is through the MCU control circuit unit; Compare computing; Carry out exporting 4～20mA simulating signal by the D/A converting unit after the data processing according to sampled value, realize the level gauging of capacitance object position transmitter; Simultaneously, HART communication interface electric circuit inspection demodulates the digital signal of stack to the external control signal that is superimposed upon on 4～20mA direct current signal, sends CPU to and handles; Process result is the alternating signal of HART semaphore request and is superimposed upon on the direct current signal through HART communication interface circuit modulation conversion, thus the digital communication of realization and external information.Among the present invention, main variables and control information are transmitted by 4～20mA, and under the situation of needs, other procedure parameters, device configuration, calibration and configuration info are visited with the mode of digital communication through the HART agreement.
Inner integrated 12 bit A/D converters of MCU control module, have super low-power consumption and can directly drive LCD, can save many peripheral chips, simplify hardware circuit design greatly up to the FLASH storer of 60KB and the RAM of 2KB.
The HART communication interface is with MCU and the HART MODEM chip development capacitance object position transmitter based on the HART communication, and is simple and convenient, dwindled space and cost.The main functional modules of HART MODEM is made up of steering logic, carrier wave detection, modulation and demodulation four parts.The function of it is integrated input filtering and output Shaping can be simplified the reliability of interface circuit design realization system.
The HART communication interface mainly is made up of MCU interface and transformer coupled interface.MCU itself has the communication interface that serial ports can be used as itself and HART MODEM, and is as shown in Figure 2.
When occurring the frequency signal of 1200 (± 10) Hz or 2200 (± 20) Hz on the IRXA pin of HART chip A5191; Then the OCD pin of A5191 is a high level; MCU puts high level with P1.3 after P1.6 detects high level; This moment, the INRTS pin of HART MODEM detected high level, opens detuner detected digital signal is carried out demodulation and send valid data to MCU by ORXD handling.
If OCD is low level, explain that bus is idle, the P1.3 of MCU setting at this moment also is a low level, then the modulator of A5191 is opened, and is sent by the OTXA pin after the data-modulated shaping that will receive from ITXD.Data by OTXA sends are transformer coupled to 4～20mA direct current signal by operational amplifier amplification and process.
The HART agreement adopts the Bell202 frequency shift keying signal of standard to communicate with 1200 baud rates.Its Physical layer adopt two kinds of different frequencies (1200Hz and 2200Hz, represent respectively 2 systems 1 and 0) sinusoidal signal, be superimposed upon on 4～20mA signal and communicate, owing to the average of sinusoidal signal is 0, do not disturb direct current signal.It can make simulating signal and digital signal can carry out two-way communication simultaneously and do not interfere with each other.
What the present invention adopted is semiduplex communication, adopts the three layer model structure of simplifying, i.e. ground floor Physical layer, second layer data link layer and layer 7 application layer.Physical layer specifies the transmission method of signal, transmission medium; Data link layer has been stipulated the form of HART frame, and the link communication function realizes setting up, safeguards, terminates; Application layer regulation HART command set.Order is divided three classes, i.e. generic command, normal commands and specific command.Generic command provides all and field apparatus function associated, and these orders comprise: read manufacturing firm and device type; Read initializaing variable and unit; Read the number percent of electric current output and range; Read 4 predefined dynamic variables; Read and write 8 character items, 16 character descriptors, date; Read and write 32 character informations; Read range, unit and damping time constant; Read transducer series number and boundary; The Assembly part numeral that read-write is the most last; Write polling address.Commonly used command provides the function in the common multiple field apparatus, but is not whole.Comprise and read a group selection of 4 dynamic variables altogether; Write variable damping time; Write range; (zero setting, put maximum range) is measured in calibration; Fixing output current is set; Carry out self check; Carry out host reset; Adjustment is initial to become zero; Write initializaing variable unit; Adjustment digital-analog convertor zero point and gain; Write tansfer function; Write transducer series number; Read-write dynamic variable assignment.Specific command only provides the function to special field apparatus, and it is peculiar, not compatible to be that the present invention controls oneself.
Because HART agreement predetermined data transfer rate is 1200bit/s, 10 milliseconds around an of character of every transmission, so adopt the mode transceive data of interrupting in the software, all the other times can make CPU get into low power consumpting state or handle other affairs.The reception of the USART module of MSP430, transmission buffer memory all can produce independently and interrupt, and program is accomplished the various processing to the HART information frame in this interrupts.In the receiving course of frame, unusual whenever detecting, corresponding state information can be set automatically, program interrupts focusing on mistake, the delay that occurs in the transmission course at timer, and calls corresponding processing procedure according to the difference of system works pattern.The process of transmitting of information frame similarly; When system works during in group schema; The command information whether steady arm constantly has main frame to upload on the detection line at a certain time interval if do not have, can send the form of the relevant information of equipment operation with the HART information frame automatically; If just there is main frame to communicate by letter, then preferentially carries out Host Command, or postpone or cancel the transmission of burst data according to the Host Command type.
Claims (4)
1. capacitance object position transmitter based on the HART communication; It is characterized in that; Capacitance object position transmitter based on the HART communication; Comprise with MCU being MCU control circuit unit, signal processing unit, AD conversion unit, D/A conversion unit and the HART communication interface of core, signal processing unit is changed sensor signal, and the capacitance of measuring is adjusted to the correspondent voltage value; Magnitude of voltage is sent into the collection that AD conversion unit carries out data, and data are admitted to the MCU control circuit unit; After the MSP430 single-chip microcomputer of MCU control circuit unit obtained communication of HART communication interface or the instruction through man-machine interface, MCU control circuit unit output image data signal converted standard signal output into to D/A conversion unit; Signal processing unit comprises square-wave generator, first gating switch, BPF., voltage follower, sensor, voltage current adapter, second gating switch, phase-sensitive detector (PSD), low-pass filter successively; When sending into first gating switch, the square wave that square-wave generator sends sends into the phase-sensitive detector (PSD) of rear end; Voltage follower output signal is delivered to second gating switch through the synchronous signal of sensor, and MCU control circuit unit output signal control signal second gating switch is selected sensor signal.
2. according to the said capacitance object position transmitter based on the HART communication of claim 1, it is characterized in that said HART communication interface mainly is made up of MCU interface and transformer coupled interface, MCU itself has serial ports and can be used as the communication interface with HART MODEM.
3. method of work based on the capacitance object position transmitter of HART communication; Comprise capacitance object position transmitter based on the HART communication; It is characterized in that said signal processing unit compares computing with the simulating signal process MCU control circuit unit of sensor sample; Carry out exporting 4～20mA simulating signal by D/A conversion unit after the data processing according to sampled value, realize the level gauging of capacitance object position transmitter; Simultaneously, HART communication interface electric circuit inspection demodulates the digital signal of stack to the external control signal that is superimposed upon on 4～20mA direct current signal, and the CPU that sends the MCU control circuit unit to handles; Process result is that the alternating signal of HART semaphore request and being superimposed upon on the direct current signal is seen off through HART communication interface circuit modulation conversion.
4. according to the method for work of the said capacitance object position transmitter based on the HART communication of claim 3; It is characterized in that; Said HART agreement adopts the Bell202 frequency shift keying signal of standard to communicate with 1200 baud rates; Its Physical layer adopts the sinusoidal signal of 1200Hz and two kinds of different frequencies of 2200Hz, is superimposed upon on 4～20mA signal to communicate.
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Cited By (7)
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| CN103576643A (en) * | 2012-08-10 | 2014-02-12 | Ls产电株式会社 | HART analog input module with differential input stage |
| CN103701789A (en) * | 2013-12-20 | 2014-04-02 | 重庆川仪自动化股份有限公司 | Instrument communication module and method |
| WO2014146243A1 (en) * | 2013-03-19 | 2014-09-25 | General Electric Company | Current loop voltage modulator for communication interface |
| US9008197B2 (en) | 2013-07-26 | 2015-04-14 | General Electric Company | Current loop voltage modulator for communication interface |
| CN107091666A (en) * | 2017-06-15 | 2017-08-25 | 上海诺仪表有限公司 | Digital communication apparatus and method, the mass flowmenter of a kind of mass flowmenter |
| CN107421631A (en) * | 2017-06-28 | 2017-12-01 | 沈阳振科仪表有限公司 | A kind of relay exports vibration velocity transmitter |
| CN111780828A (en) * | 2020-06-18 | 2020-10-16 | 东风汽车集团有限公司 | Method for calculating actual fuel percentage of fuel tank |
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103576643A (en) * | 2012-08-10 | 2014-02-12 | Ls产电株式会社 | HART analog input module with differential input stage |
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| CN103701789A (en) * | 2013-12-20 | 2014-04-02 | 重庆川仪自动化股份有限公司 | Instrument communication module and method |
| CN107091666A (en) * | 2017-06-15 | 2017-08-25 | 上海诺仪表有限公司 | Digital communication apparatus and method, the mass flowmenter of a kind of mass flowmenter |
| CN107421631A (en) * | 2017-06-28 | 2017-12-01 | 沈阳振科仪表有限公司 | A kind of relay exports vibration velocity transmitter |
| CN107421631B (en) * | 2017-06-28 | 2023-07-28 | 沈阳振科仪表有限公司 | Relay output vibration speed transmitter |
| CN111780828A (en) * | 2020-06-18 | 2020-10-16 | 东风汽车集团有限公司 | Method for calculating actual fuel percentage of fuel tank |
| CN111780828B (en) * | 2020-06-18 | 2021-06-04 | 东风汽车集团有限公司 | Method for calculating actual fuel percentage of fuel tank |
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Application publication date: 20120704 |