Design and application of the hottest field type p

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Design and application of field process instrument calibrator

1 introduction

with the development of production process automation technology, in order to ensure the safe and reliable operation of the production process, it is necessary to maintain and calibrate the instruments used in the production process at any time. The traditional method of taking the instruments used in the production process back to the laboratory for calibration can no longer meet the requirements of production. Instead, the instruments are calibrated directly on site. According to this trend, many famous foreign instrument manufacturers have launched their own field type process instrument calibrators, such as the F710 series of fluke company in the United States, the CA10 series of Yokogawa company in Japan, and so on. In addition to meeting the requirements of function, application range and accuracy, this kind of calibrator should also have the ability to adapt to the environment of temperature, humidity changes, water splashes and accidental falls. In addition, in order to ensure the accuracy index of the calibrator, it should also be able to easily trace to the national standard. In response to these requirements, Shenzhen shengligao Electronic Technology Co., Ltd. has developed vc10 series process instrument calibrators, which can accurately output and measure process signals such as voltage, current, resistance, temperature, frequency and pressure through simple button operation on the panel, and has complete input and output protection functions. This series of products adopts large character LCD display, a single 9V battery or AC power adapter for power supply, and the structural design of shock proof, dust-proof and splash proof. Its volume is like an ordinary handheld digital multimeter, which is especially suitable for the calibration and maintenance of various instruments in the industrial control process on site. The panel calibration technology adopted by the product makes it easy to trace the source of the instrument to the upper level of the annual production capacity of 50000 tons of lithium-ion cathode material and 10billion watt hour power battery. Now take the representative vc14 and VC15 in vc10 series as examples to illustrate their design methods

2 hardware circuit design

in order to meet high accuracy (0.02% range) and resolution (0.001% range), 20 bit DAC and ADC are used for output and input respectively. In order to improve the stability and reduce the impact of the external environment, the adjustable components such as potentiometers are removed from the machine, and the microprocessor automatically carries out an internal calibration at the specified time to eliminate various effects. Since the signal ranges of vc14 and VC15 are different, their circuits are also slightly different, which are described separately

2.1 hardware circuit design of vc14 temperature calibrator

vc14 is mainly used for the calibration and inspection of temperature display instruments and sensors, so it has 7 graduation marks (R, s, J, K, e, t, b) thermocouples and 2 scores, which are more suitable for the testing of the wear resistance of printing ink layer, the wear resistance of PS plate photosensitive layer and the wear resistance of surface coating of related products. The simulation and measurement functions of thermal resistance of experimental grade numbers (PT100, cu50), For instruments and sensors other than these graduation marks, its MV and Ω functions can be used. Its principle is actually to output a corresponding MV or Ω signal according to the graduation meter, or measure an MV and Ω signal, and then convert it into the corresponding temperature for display according to the graduation meter. Because the instrument uses 20 bit DAC and ADC inside, it has high precision and resolution. The working principle is shown in Figure 2-1. Voltage and thermocouple output: the operator selects the voltage or thermoelectricity through the input/output and fun function keys of the panel. Everyone selects the output function of this kind of equipment in combination with their usual material characteristics to be tested. The microprocessor controls the switch K1 to connect the common terminal "C" and "V"

at this time, the output value set by the operator through the panel is converted into D value by the microprocessor, so that the output of the instrument changes. Because the D value is 0 ~ 220, the Voh range of the instrument output is 0 ~ K1 · VREF, and the resolution is about 1ppm (one millionth). The value of K1 is changed by the rang key on the user's operation panel, so that the instrument outputs signals of different ranges

resistance and thermal resistance output: the operator selects the resistance and thermal resistance output function through the fun function key on the panel, and the microprocessor controls the switch K1 to connect the common end 'C' and 'Ω' ends. At this time, there must be an excitation current I outside the instrument, and the reference input VREF of the DAC = I ·

measure the voltage and thermocouple: the operator selects the input voltage measurement through the in put/output and fun keys on the instrument panel, The microprocessor

controls K2 to the 'V' end. At this time, the ADC conversion value d = through the rage key, the microprocessor adjusts the K2 magnification, so that when vinhl changes from 0 to the full point of the range, D is 0 ~ 2 n (n = 20); The resolution can reach 1ppm, and the converted D value is changed into the corresponding display value by the microprocessor and sent to the LCD for display

measure resistance and thermal resistance: the microprocessor controls K2 to turn to the 'Ω' end. At this time, if a measured resistance Rx is connected between the input terminal HL, adjust the magnification of K2 so that d changes from 0 to 2 n when RX changes from 0 to full scale, and the resolution can reach 1ppm. After conversion, the D value is changed into the corresponding display value by the microprocessor and sent to the LCD for display

vc14 when simulating and measuring thermocouples, it has the function of automatic compensation of cold end temperature, which can comprehensively carry out the quality upgrading project. The internal microprocessor controls K3 every 10s to connect 'C' and 'R'. The output of the internal temperature sensor is sent to ADC to convert into the corresponding value, which is sent to the microprocessor to correct the current output value or measured value

2.2 hardware circuit design of VC15/MA calibrator

vc15 is mainly aimed at the calibration and inspection of instruments (such as transmitters) that use standard current and voltage signals on the process site. It is designed to output and measure DCV and DCA, simulate the output of transmitters, and provide 24V loop voltage and measure current at the same time. Like vc14, 20 bit DAC and ADC are used internally. The working principle is shown in Figure 2-2

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