在工厂有广泛的应用，为保证其正常运行及准确性，定期检查、校准是很有必要的。 Differential pressure transmitters are widely used in factories. To ensure their normal operation and accuracy, regular inspection and calibration are necessary. A method for on-site calibration without removing the impulse tube is now introduced.
We know that the differential pressure transmitter is connected to the impulse tube in the application. Generally, the connection between the impulse tube and the differential pressure transmitter needs to be disconnected, and then connected to the pressure source for calibration. This is very troublesome, and the work and labor intensity are high,
The most worrying is to break the pressure tube or leak when disassembling the joint. We know that no matter what type of differential pressure transmitter, its positive and negative pressure chambers have vents, drain valves or cocks; this facilitates our on-site calibration of differential pressure transmitters.
This means that the differential pressure transmitter can be calibrated without removing the impulse 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 unscrew the exhaust, drain valve or cock to vent, and then replace it with a homemade connector.
Replace the exhaust, drain valve or cock of the positive pressure chamber; while the negative pressure chamber is kept loose, allowing it to vent to the atmosphere. The pressure source is connected to the self-made joint through a rubber tube, the balance valve is closed, and the gas circuit is sealed, and then the ammeter (voltmeter), the hand
The controller is connected to the output circuit of the transmitter, and calibration is started after power-on and warm-up.
的校准 Calibration of conventional differential pressure transmitters
First adjust the damping to zero, first adjust the zero point, and then add the full-scale pressure to adjust the full scale so that the output is 20mA. The on-site adjustment is fast. Here we introduce the quick adjustment method of zero and range. Zero adjustment has almost no effect on full scale, but zero adjustment when full scale
It has an impact. Without migration, the effect is about one-fifth of the range adjustment, that is, the range is adjusted upward by 1mA, and the zero point will move upward by about 0.2mA, and vice versa. For example: input full-scale pressure is 100Kpa, the reading is 19.900mA, adjust the range potentiometer to make the input
The output is 19.900+ (20.000-19.900) × 1.25 = 20.025mA. When the range is increased by 0.125mA, the zero point is increased by 1/5 × 0.125 = 0.025. The zero adjustment potentiometer makes the output 20.000mA. The zero and full scale adjustments are normal. After that, check the middle scales,
See if it is too bad? Make fine adjustments if necessary. Then adjust the migration, linearity, and damping.
的校准 Calibration of smart differential pressure transmitter
It is not possible to calibrate the smart transmitter with the conventional method described above, because this is determined by the structure principle of the HART transmitter. Because the smart transmitter is between the input pressure source and the 4-20mA current signal generated, in addition to the mechanical and electrical circuits, there is a microprocessing core.
The chip works on input data. Therefore, calibration is different from conventional methods.