How to correct calibrate pressure transmitter
How to correct calibrate pressure transmitter ?
The real calibration of Smart pressure transmitter that it need a pressure source and input pressure transmitter 's
pressure.Since the range (LRV, URV) is not calibrated without the use of a standard, ignoring the input section
(input of the transmitter) for output regulation (transmitter's conversion circuit) is not the correct calibration.
Furthermore, the relationship between the pressure and differential pressure detecting components and the
A/D conversion circuit and current output is not equal. The purpose of calibration is to find the relationship between
the three. One point to emphasize: Only the input and output (input transmitter pressure, A / D conversion circuit,
loop current output circuit) can be called a true calibration.
一， preparation work ：
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.
二, the calibration of the conventional differential pressure transmitter:
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.
三，the calibration of the intelligent differential pressure transmitter ：
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.
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