CN201974211U

CN201974211U - Capacitance level transmitter based on HART (Highway Addressable Remote Transducer) communication

Info

Publication number: CN201974211U
Application number: CN2010206477312U
Authority: CN
Inventors: 王鑫; 杨振荣
Original assignee: Shanghai Automation Instrumentation Co Ltd
Current assignee: Shanghai Automation Instrumentation Co Ltd
Priority date: 2010-12-08
Filing date: 2010-12-08
Publication date: 2011-09-14
Anticipated expiration: 2020-12-08

Abstract

The utility model relates to a capacitive level transmitter based on HART communication. The capacitive level transmitter based on HART communication adds digital communication function on the basis of the two-wire capacitive level transmitter, and adopts Bell202FSK The signal standard allows the digital signal and the analog signal to be transmitted simultaneously without interfering with each other, realizing two-way communication, and at the same time improving the measurement accuracy and utilization rate of the capacitive level transmitter, which is convenient for installation, adjustment and maintenance And control, reducing the cost of control. It greatly enhances its role in the field of detection and control.

Description

Capacitance object position transmitter based on the HART communication

Technical field

The utility model 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 modernized industry, production scale is big, the speed height, and high temperature, high pressure, severe corrosive or inflammable and explosive material are often arranged, most important especially for the supervision and the automatic control of thing position.Therefore, thing position detection technique accounts for critical role in the industrial process control of modernization.Level transmitter in the power station, industrial circle such as petrochemical industry, oil field is widely used.By 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 provide useful information 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 to 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, mainly as class 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 measuring the thing 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, a kind of level meter that is most widely used.

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 by 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 utility model is the problem that can't realize digital communication at existing capacitance object position transmitter, a kind of capacitance object position transmitter based on the HART communication has been 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, strengthened its effect in the Detection ﹠ Controling field greatly.

The technical solution of the utility model 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 is carried 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 by man-machine interface, MCU control circuit unit output image data signal was converted to standard signal output to D/A conversion unit; Signal processing unit comprises square-wave generator, first gating switch, bandpass filter, 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, the 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.

Described HART communication interface mainly is made of MCU interface and transformer coupled interface, and MCU itself has serial ports and can be used as communication interface with HART MODEM.

The beneficial effects of the utility model are: the utility model is based on the capacitance object position transmitter of 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 of the utility model based on the HART communication interface;

Fig. 2 is the utility model single-chip microcomputer 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 by man-machine interface, MCU control circuit unit 1 output image data signal was converted to corresponding 4～20mA output to D/A converting unit 4; HART communication interface 5 also comprises the modulation-demodulation circuit that is made of special-purpose HART modem chip.Signal processing unit 2 comprises square-wave generator 21 successively, first gating switch 22, bandpass filter 23, voltage follower 24, sensor 25, voltage current adapter 26, second gating switch 27, phase-sensitive detector (PSD) 28, low-pass filter 29, 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 utility model is by 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; The result who handles 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.In the utility model, 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 in the mode of digital communication by 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.

HART communication interface usefulness MCU and HART MODEM chip development are based on the capacitance object position transmitter of HART communication, and be 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 that interface circuit design realizes system.

The HART communication interface mainly is made of MCU interface and transformer coupled interface.MCU itself has the communication interface that serial ports can be used as itself and HART MODEM, as shown in Figure 2.

When occurring the frequency signal of 1200 (± 10) Hz or 2200 (± 20) Hz on the IRXA of the A5191 pin, 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, the bus free time be described, 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.Transformer coupled to 4～20mA direct current signal by the data that OTXA sends 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 because 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.

Claims

1. A capacitive level transmitter based on HART communication, characterized in that the capacitive level transmitter based on HART communication includes an MCU control circuit unit, a signal processing unit, and an analog-to-digital conversion with MCU as the core Unit, digital-to-analog conversion unit and HART communication interface, the signal processing unit converts the sensor signal, and adjusts the measured capacitance value to the corresponding voltage value; the voltage value is sent to the analog-to-digital conversion unit for data collection, and the data is sent to the MCU Control circuit unit; after the MSP430 microcontroller of the MCU control circuit unit receives the HART communication interface communication or the instruction through the man-machine interface, the MCU control circuit unit outputs the collected data signal to the digital-to-analog conversion unit to convert it into a standard signal output; the signal processing unit in turn includes square Wave generator, first gating switch, bandpass filter, voltage follower, sensor, voltage-to-current converter, second gating switch, phase-sensitive detector, low-pass filter, square wave from square wave generator When it is sent to the first strobe switch, it is sent to the back-end phase-sensitive detector. The output signal of the voltage follower passes through the sensor and the signal is sent to the second strobe switch. The MCU control circuit unit outputs the signal to control the signal for the second strobe switch to select. sensor signal.

2. The capacitive level transmitter based on HART communication according to claim 1, wherein said HART communication interface is mainly composed of MCU interface and transformer coupling interface, and MCU itself has a serial port which can be used as a connection with HART MODEM. Communication Interface.