How to verify the pressure transmitter

First, the true calibration of the pressure transmitter requires a standard pressure source to be input to the transmitter. Since the range (LRV, URV) is not calibrated without the use of a standard, ignoring the input section (pressure input to the transmitter) for output regulation (transfer circuitry of the transmitter) is not the correct calibration.

Furthermore, the relationship between the pressure and differential pressure detecting components, the A/D conversion circuit, and the current output is not equal. The purpose of the calibration is to find the relationship between the three. The pressure source is connected to the self-made joint through the rubber tube, the balance valve is closed, and the air circuit sealing condition is checked, and then the ammeter (voltmeter) and the hand-held device are connected into the output circuit of the transmitter, and the calibration is started after the power is preheated. We know that no matter what type of differential pressure transmitter, the positive and negative pressure chambers have exhaust, drain valve or cock; this is convenient for us to calibrate the differential pressure transmitter on site, that is to say, it is not necessary to remove the guide. The differential pressure transmitter can be calibrated by the pressure tube. When calibrating the differential pressure transmitter, first close the positive and negative valves of the three-valve group, open the balance valve, and then loosen the exhaust, drain valve or cock to empty, and then replace the positive pressure chamber with a self-made joint. The exhaust, drain valve or cock; while the negative pressure chamber remains loose, allowing it to pass through the atmosphere.

First adjust the damping to zero state, first adjust the zero point, then adjust the full scale pressure to full scale, so that the output is 20mA, the on-site adjustment is fast, here introduces the zero adjustment of the zero point and range. Zero adjustment has almost no effect on fullness, but the fullness has an effect on zero. When there is no migration, the effect is about 1/5 of the range adjustment, that is, the range is adjusted upward by 1 mA, and the zero point will move upward by about 0.2 mA. ,vice versa. It is not acceptable to calibrate the smart transmitter using the conventional method described above, as this is determined by the structural principle of the HART transmitter. Because the smart transmitter is between the input pressure source and the generated 4-20 mA current signal, in addition to the mechanical and electrical circuits, there is also the operation of the microprocessor chip on the input data. Therefore, the adjustment is different from the conventional method.

The actual pressure transmitter can be calibrated as follows:

1. Make a 4-20 mA trimming to correct the D/A converter inside the transmitter. Since it does not involve sensing components, no external pressure source is required.

2. Perform a full fine-tuning to match the 4-20 mA, digital reading to the actual applied pressure signal, thus requiring a pressure source.