Pressure transmitter is a kind of commonly used measuring instrument, which can convert the physical parameters such as gas and liquid sensed by load cell into standard signal output.
It has the advantages of measurement, stable performance, high sensitivity and easy operation.
Figure 1: ABB Transmitter 264DSFSHB2B3
In order to ensure the normal operation of the pressure transmitter, users need to calibrate the product, so do you how to calibrate the pressure transmitter?
First, the true calibration of the pressure transmitter requires that we use a standard pressure source to input the transmitter. Since range adjustment (LRV, URV) is not calibrated without using a standard transmitter, it is incorrect to adjust the output (the converting circuit of the transmitter) by ignoring the input (pressure of the input transmitter).
Secondly, the relationship between pressure and differential pressure detection components and A/D conversion circuit and current output is not equal. The purpose of calibration is to find out the change relationship of these three components.
The pressure source is connected to the self-made joint by the rubber hose, closing the balance valve and checking the sealing of the gas path.Then we need to plug the ammeter (voltmeter) and the hand operator into the transmitter output circuit and start calibration after the power is warmed up.
We know that no matter what type of a differential pressure transmitter is, its positive and negative pressure chambers have exhaust, drain valves or cocks. This makes it easy for us to calibrate the differential pressure transmitter on-site, which means that the differential pressure transmitter can be calibrated without removing the pressure guide tube.
When calibrating the differential pressure transmitter, we must first close the positive and negative valves of the three valve groups, open the balance valve, and then loosen the exhaust valve, drain valve or cock to vent.
Finally, replace the exhaust valve, drain valve or cock connected to the positive pressure chamber with a homemade joint.The negative pressure chamber, on the other hand, remains in a state of looseness to allow it to pass through the atmosphere.
We need to first adjust the damping to zero, then zero, then full degree pressure to full range, so that the output is 20 mA.
Quick adjustment is emphasized in the industrial field. Quick adjustment of zero point and range is introduced here: zero point has little effect on full degree, but it has effect on zero point when full degree is adjusted.
In the case of no migration, the influence of full-scale adjustment on the zero point is about 1 / 5 of the range adjustment, that is, if the range is adjusted up 1 mA, the zero point will move up about 0.2 mA, and vice versa.
Figure 2: ABB Transmitter 15936 T 026169
It is not feasible to calibrate the smart transmitter with the above-mentioned conventional method, because the calibration of the smart transmitter is determined by the structural principle of the HART transmitter.
Between the input pressure source and the 4-20mA current signal generated by the smart transmitter, in addition to the mechanism and the circuit, there is also a micro-processing chip for computing the input data.
Therefore, the adjustment is different from the conventional method.
1.Make a 4-20mA fine-tuning first to correct the D/A converter inside the transmitter.
Because it does not involve sensing components, no external pressure signal source is required.
2.Make another full-range fine-tuning to match the 4-20mA, digital readings with the actual applied pressure signal, so a pressure signal source is required.