Design of smart card for electromagnetic flowmeter

2022-06-23
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Using Fieldbus to design electromagnetic flowmeter smart card

nowadays, fieldbus technology is developing with each passing day, and its application fields are becoming more and more extensive, from home, energy, building to industrial field. This paper will introduce the design of smart card of electromagnetic flowmeter based on fieldbus

in order to meet the needs of the market, major companies at home and abroad have launched a new generation of intelligent flow meters with their own characteristics. Among them, the development of intelligent electromagnetic flowmeter combined with fieldbus technology is particularly eye-catching, which is determined by the characteristics of electromagnetic flowmeter

1) among various flow instruments, electromagnetic flowmeter involves the most intelligent functions. The application of intelligent technology is not only conducive to improving the performance of electromagnetic flowmeter, but also easy to combine with fieldbus technology

2) electromagnetic flowmeter has a wide range of uses. From river basin governance to community construction, especially the development of emerging environmental protection industries, steel mills will further promote the application of electromagnetic flowmeter at this stage because they are not willing to raise the purchase price again

the advantage of fieldbus technology is to simplify the monitoring and management of field devices, and gradually replace the traditional decentralized control system with network management. Intelligent electromagnetic flowmeter, with its own intelligent technology and fieldbus technology, will greatly meet the requirements of its application in various fields. At present, the bus technologies widely used in the industrial field in China include HART communication protocol, foundation fieldbus, LonWorks technology, etc. the following introduces the design of smart card when the intelligent electromagnetic flowmeter is combined with these fieldbuses

hart

hart (highway addressable remote translator) protocol is a transitional protocol. It uses FSK technology to superimpose a frequency signal on the 4 ~ 20mA process measurement analog signal, so that the analog signal and digital two-way communication can be carried out at the same time without mutual interference. At present, there are still a large number of 4 ~ 20mA standard analog instruments in the industrial field in China. HART protocol plays a connecting role and has been widely used in China

1. Considering the combination with HART protocol, the three CPU scheme is adopted when designing the smart card of electromagnetic flowmeter. The CPU adopts the 68HC11 single chip microcomputer of Motorola Company. This type of chip has the characteristics of small size, low power consumption and simple system design. It is the most powerful series among all 8-bit single chip microcomputers. CPU1 controls a/d sampling, d/a conversion, data processing and Hart command interface; CPU2 generates rectangular wave excitation signal and wide pulse sampling signal (although CPU2 has few tasks and simple functions, its reliable operation is the guarantee for the normal operation of the whole instrument, so a single chip microcomputer is used to realize these functions); Cpu3 manages keyboard operation and LCD display (the interface between cpu3 and smart board can be made into plug-in type, and whether cpu3 is required can be selected by the user). The communication between the three CPUs adopts synchronous serial spi mode, CPU1 is the master, CPU2 and cpu3 are the slaves

2. The a/d conversion circuit adopts AD7715 chip, which is a chip used for low-frequency measuring instruments. It has the advantages of 16 bit error free resolution and good anti-interference. It can amplify and convert unipolar input and bipolar input signals. In the design of smart card, AD7715 chip uses 5V single power supply and +2.5v bipolar signal input. The input pin, output pin and serial clock input pin of serial data are directly connected with the SPI port of CPU1

3. The loop power supply chip AD421 is used in the d/a conversion circuit. Its 16 bit resolution and 60.01% nonlinearity are particularly suitable for the design of Hart intelligent instruments. The built-in voltage regulator of AD421 provides + 5V power supply and also supplies power to modem. It is connected with CPU1 through serial interface. The digital signal output by CPU1 directly enters the data input pin of AD421. At the same time, connect the AD421 with the modem chip of HART protocol, and the 1200Hz and 2200Hz modulated sine waves can be added to the current loop output by the AD421 chip, so that the digital signal and analog signal can be output at the same time

4. The modulation and demodulation chip (modem) is ht2012 produced by smart company, which is specially designed and produced for Hart products. The demodulator obtains the FSK signal through irxa. After demodulation, the FSK signal outputs a digital signal in the orxd, which is directly connected to the asynchronous serial input port of CPU1. The modulator obtains the digital signal of CPU1 asynchronous serial output port through itxd. The modulated signal outputs FSK signal in otxa, and the FSK signal is loaded into 4 ~ 20mA output circuit after shaping. The inrts starts the modem to output the FSK signal, and the OCD is used as the carrier sense output. When the irxa has the FSK signal, it changes to the low level, and starts CPU1 to read the demodulation signal at the orxd. Since the input signal of the demodulation part of ht2012 chip is from the 4 ~ 20mA loop, the signal must pass through the band-pass filter to remove the environmental noise interference, and be converted into a square wave through the trigger to enter irxa. The input signal of the modulation part is taken from the asynchronous serial output port of CPU1, and the signal must be loaded into the 4 ~ 20mA loop through the shaping circuit after modulation

Foundation Fieldbus (FF)

foundation fieldbus is a fully distributed automation system. Its open digital communication capability enables the automation system to have networking characteristics. The main functions to be completed are to measure, signal transmission, control, display, and calculate various parameters in the industrial production process, so as to realize the automatic detection, monitoring, and automatic adjustment of the production process Sequence control and self-protection. In terms of communication mode, for example, China's rare earth output ranks first in the world, and all digital communication is adopted. Because the FF system completely decentralizes the control function to the field, it is required that only the field instruments can realize the complete control function, that is, in addition to measuring and calculating, the field instruments can communicate with each other to receive, send and control. With its significant advantages, the intelligent electromagnetic flowmeter can not only fully meet the needs of the FF Bus, but also simplify its own hardware circuit and reduce the cost, Improve the reliability of instruments

at present, many companies produce chips that can be used as foundation fieldbus communication controllers, such as Yokogawa and Fuji in Japan, shipstar in the United States, and SMAR in Brazil. The FB3050 chip produced by SMAR company was selected for the ninth five year plan project "development of intelligent electromagnetic flowmeter conforming to FF Protocol"

1. The chip complies with the fieldbus physical layer standard specified in SP part2. The chip is designed to consider the interface with various popular microprocessors, which can be used as the communication interface of the master device and the slave device on the fieldbus. In order to reduce the burden of CPU, FB3050 has designed an automatic identification processor for data link layer address and frame, and provided a set of logic mechanism for automatically identifying frame control word and frame destination address. With this mechanism and DMA circuit, FB3050 can correctly receive all information frames belonging to this node from the top without CPU intervention

2. The CPU on the board adopts intel80188 chip, which is most commonly used in embedded control. 80188 has 1MB Memory Space and 64KB maximum IO addressing space. It integrates a set of interrupt controllers, two-way DMA controllers, three 16 bit timers to realize value-added services such as spot warehousing, logistics distribution and warehouse order pledge, six programmable memory chip selection lines and seven programmable IO interface chip selection lines. In view of the rich resources of 80188 chip, when designing the flowmeter smart card, the functions in CPU1 in the smart board of Hart intelligent electromagnetic flowmeter can be completely moved up to intel80188 chip in the FF board

3. AD7715 chip is still selected as the a/d sampling circuit. Its data input and output lines are connected to the i/o port line of 80188, and the drdy data ready line is connected to the interrupt line INT1. 80188 turns on the interrupt when the timer expires. When drdy is at low level, it indicates that the data is ready. The interrupt responds and enters the interrupt sampling processing program. The original CPU2 and cpu3 can still be retained (cpu3 is selected by the user), and its SPI port line can be connected with the i/o line of 80188 to communicate in analog SPI mode. Because the FF Bus is all digital communication, the Ma circuit part can be omitted

lonworks bus

lonworks bus is introduced by echelon company of the United States. It is a relatively perfect and excellent field bus standard. LonWorks is a bus product based on network technology, which has been widely used in the United States and other places. There are many successful application examples in China. Combined with the OEM cooperation mode of echelon company, LonWorks bus technology will have a broader application prospect in China. Therefore, it is necessary to apply this technology to intelligent electromagnetic flowmeter

lonworks field control network is a local operation network, which provides a strong implementation means for the distributed monitoring system. Because the router is used in the system, the network is not limited by the communication medium, communication distance and communication rate. The combination of intelligent electromagnetic flowmeter and LonWorks technology not only facilitates users, but also expands the application field of electromagnetic flowmeter

in LONWORKS bus, each field device is called a node. A typical field control node mainly includes the following functional blocks: application CPU, i/o processing unit, communication processor, transceiver and power supply. The core of LonWorks technology is the neuron chip, which is the communication coprocessor of nodes to coordinate the communication and control between hosts and nodes, as well as the information communication between nodes. Because the neuron chip mainly uses the resources of the advanced host to complete the complex measurement and control functions, its peripheral circuit is simple and small, and can be made into a plug-in interface with the instrument communication card. In this way, when designing the circuit, the universality of the instrument communication card is maintained, and the anti-interference ability is improved, so that the instrument can still independently complete the monitoring and control functions when the network is busy

the wide application of fieldbus technology is the trend and necessity of the development of industrial automation. It is the direction that every engineer and technician should recognize and make active efforts to better combine fieldbus technology with industrial instruments in the near future. (end)

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