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Pressure transmitter calibration steps
The pressure transmitter is a kind of measuring instrument which is mainly used for measurement and has a certain application in many fields. Pressure transmitters need to be calibrated when they are used, and pressure transmitters need correct methods when they are calibrated.
Prepare the calibration method
The standard pressure source is connected to the self-made connector through the rubber hose, the balance valve is closed, and the gas seal is checked. Then the ammeter (voltage meter) and the HART communicator are connected to the output circuit of the pressure transmitter, and the power is warmed up. calibration. The positive and negative pressure chambers of the differential pressure transmitter have exhaust, drain valves or cocks; it is convenient for us to calibrate the differential pressure transmitter in the field, that is to say, the differential pressure transmitter can be calibrated without removing the pressure guiding tube. Device. When calibrating the differential pressure transmitter, first close the positive and negative valves of the three valve group, open the balancing valve, and then loosen the exhaust, drain valve, or tap to vent. Then replace the positive pressure chamber with a self-made connector. The exhaust, drain valve, or cock; while the negative pressure chamber is kept unscrewed, making it open to the atmosphere.
Conventional pressure transmitter calibration
First adjust the damping to the zero state, first adjust the zero point, then increase the pressure to full range, so that the output is 20mA, and the adjustment in the field is fast. Here, we introduce the zero and span quick adjustment method. Zero adjustment has almost no effect on fullness, but when fullness has an effect on the zero point, its effect is approximately 1/5 of the span adjustment without migration, ie 1mA of span is adjusted upwards and the zero point will move approximately 0.2mA upwards. ,vice versa.
Smart pressure transmitter calibration
It is not possible to calibrate the smart transmitter using the above-mentioned conventional method because it is determined by the structural principle of the HART transmitter. Because the smart pressure transmitter is between the input pressure source and the generated 4-20mA current signal, in addition to the mechanical and electrical circuits, there is also a microprocessor chip to calculate the input data. Therefore, the adjustment is different from the conventional method.
Actually, the calibration of the intelligent pressure transmitter by the manufacturer Shaoxing Zhongyi is also explained. For example, ABB's transmitters have the following points: “set rangeâ€, “heavy rangeâ€, and “fine adjustmentâ€. The "set range" operation is mainly through the digital setting of LRV and URV to complete the configuration work, while the "re-quantity range" operation requires the pressure transmitter to be connected to a standard pressure source and guided by a series of instructions. The pressure transmitter senses the actual pressure directly and sets the value. The initial and final setting of the range depends directly on the actual pressure input value. However, to see that although the analog output of the pressure transmitter is correctly related to the input value used, the digital value of the process value shows a slightly different value, which can be calibrated by the trimming item. Because each part needs to be adjusted separately and must be adjusted together, the following steps can be performed during actual calibration: The HART Communicator can use the HART375 communicator from Shaoxing.
Debugging method
1. First perform a 4-20mA trim to calibrate the D/A converter inside the pressure transmitter. Since it does not involve sensing components, no external pressure signal source is required.
2. Do a full fine-tuning again so that the 4-20mA, digital readout matches the actual applied pressure signal, so a pressure signal source is needed.
3, finally do heavy ration, through the adjustment of the analog output 4-20mA and the additional pressure signal source, its role and the transmitter shell zero (Z), adjust the range (R) switch is exactly the same role .