Differential pressure transmitter is widely used in the factory. It is necessary to check and calibrate regularly to ensure its normal operation and accuracy. This paper introduces a method of field calibration without dismantling the guide tube.

First, the preparation work:

We know that the differential pressure transmitter is used in the application is connected with the pressure guide pipe, the usual practice, the need to guide the pressure pipe and differential pressure transmitter connector open, and then access the pressure source calibration. This is very troublesome, and the intensity of work and labor, the most worried about is the disassembly and assembly of the pressure pipe when pulling off or leakage. We know that no matter what type of differential pressure transmitter, the positive and negative pressure chamber are exhaust, exhaust valve or cock; this is our site calibration of differential pressure transmitter provides a convenient, that is not removed the pressure guiding pipe can be calibrated pressure transducer. The calibration of the pressure transducer, the positive and negative valve three valve closed, open balance valve, then unscrew exhaust, exhaust valve or cock vent, and then used a homemade joint instead of exhaust, connected to the positive pressure chamber of the exhaust valve or cock; while the negative pressure chamber is maintained to loosen state. The air. The pressure source is connected by a rubber tube with homemade joints, off balance valve, and check the gas seal, then the current meter (voltage meter), manipulator access transmitter output circuit, electric preheating start calibration.

Two, the calibration of conventional differential pressure transmitter:

First, the damping to zero state, the first zero adjustment, and then fill the pressure to adjust the full range, so that the output is 20mA, in the field to adjust the speed of speaking, in this paper, zero, range of rapid adjustment method. Zero to full of almost no effect, but full of zero impact, in the effect with migration is about 1 / 5 scale adjustment, namely the range to adjust 1mA, zero move up to about 0.2mA, and vice versa. For example: the full range of input pressure is 100Kpa, the reading of 19.900mA span potentiometer output to 19.900+ (20.000-19.900) * 1.25=20.025mA. range increased by 0.125mA, the zero increase of 1 / 5 x 0.125=0.025. zero potentiometer output to 20.000mA. zero and full scale adjustment is normal, and then check to see whether the middle scale, super when necessary to fine tune?. Then the migration, linear, damping adjustment work.

Three, intelligent differential pressure transmitter calibration

It is not possible to calibrate the smart transmitter with the conventional method, because it is decided by the structure principle of the HART transmitter. Because the intelligent transmitter between the input pressure source and the 4-20mA current signal, in addition to the machinery, the circuit, as well as the processing of the input data. Therefore, the adjustment and the conventional method is different. M7v#F in fact, manufacturers of intelligent transmitter calibration is also described, such as the ABB transmitter, the calibration is: "set range", "reset range", "fine tuning" of the points of the V. The setting range "operation is mainly to complete the configuration by LRV.URV digital set, and" reset "range operation requires the transmitter connected to a standard pressure source, through a series of instructions to guide and direct the actual pressure induced by the transmitter and set value. The initial and final setting of the range depends on the actual pressure input value. However, it is important to see that although the analog output of the transmitter is the correct relationship with the input value used, the numerical value of the process value is slightly different. Due to the need to separate the individual parts and the need to adjust, so the actual calibration can be carried out in the following steps:

1 do a 4-20mA fine tuning, used to correct the transmitter inside the D/A converter, because it does not involve sensing components, no external pressure signal source.

2 to do a full range of fine-tuning, so that the 4-20mA, digital reading and the actual pressure signal is applied, so the need for pressure signal source

3 do the final measurement range, by adjusting the analog output 4-20mA and the external pressure signal source, the role of the transmitter and the shell on the zero (Z), R (range) switch the same role. 2 ^8}2 C6 B. Y9 D

Problem discussion:

Some people think that, as long as the use of HART manipulator can change the range adjustment of intelligent transducer, and can be zero and span, and do not need to enter the source of pressure, but it can not be called calibration, can only be called "setting range". True calibration is required to use a standard pressure source to enter the transmitter. Because the standard range is not used (LRV, URV) is not calibrated, ignoring the input part (the pressure of the input transmitter) to adjust the output (transmitter conversion circuit) is not the correct calibration. Furthermore, the relationship between pressure, differential pressure detection components and A/D conversion circuit, current output is not equal, the purpose of the calibration is to identify the relationship between the three changes. It is emphasized that only the input and output (the pressure of the input transmitter, the A/D conversion circuit, the loop current output circuit) can be debugged together.

Four, some suggestions

After the end of the adjustment work, to the exhaust, exhaust valve or cock cycle in place, and should be wrapped with raw materials, to ensure that the screw does not leak, but before tightening should be positive, negative pressure chamber exhaust, drainage work. At this point, the process pressure can be used to carry out the simple static pressure error detection of the transmitter.