Differential pressure transmitter in the application is connected with the pressure pipe, the usual practice, the pressure pipe, and differential pressure transmitter joint needs to be separated, and then connected to the pressure source for calibration. This is very troublesome, and the work and the labor intensity is large, the most worried about is the pressure guide pipe is broken or leakage problem when disassembling and assembling the joint. We know that no matter what type of differential pressure transmitter, its positive and negative pressure chamber has exhaust, drainage valve or cock; This provides convenience 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 pipe. When the differential pressure transmitter is calibrated, close the positive and negative valves of the three valve groups, open the balance valve, and then loosen the exhaust, drain valve or cock emptying, and then use the self-made joint to replace the exhaust, drain valve or cock of the positive pressure chamber;The negative pressure chamber, on the other hand, remains rotatory, allowing it to flow through the atmosphere. The pressure source is connected with the self-made joint through the rubber tube, close the balance valve, and check the sealing condition of the gas path, then connect the ammeter (voltmeter) and the manipulator into the output circuit of the transmitter, and start the calibration after the power is preheated.
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ⅱ. Calibration of a conventional differential pressure transmitter:
First, the damping is adjusted to the zero states, the zero points is first adjusted, and then the full degree of pressure is added to the full range, so that the output is 20mA, in the field adjustment is about fast, this paper introduces the zero point, the range of fast adjustment method. Zero adjustments have almost no impact on the fullness, but it has an impact on the fullness. When there is no migration, the impact is about 1/5 of the range adjustment, that is, if the range is adjusted up by 1mA, the zero will move up by about 0.2ma, and vice versa. For example, the input full-range pressure is 100Kpa, the reading is 19.900ma, and the output of the range potentiometer is 19.900+ (20.000-19.900) ×.1.25=20.025mA. If the range is increased by 0.125mA, the zero points will be increased by 1/5 * 0.125=0.025. The zero point potentiometer will make the output 20.000mA. Fine-tune if necessary. Then the migration, linear, damping adjustment work.
ⅲ, Intelligent differential pressure transmission calibration.
It is not feasible to calibrate the intelligent transmitter with the above conventional method, because it is determined by the structural principle of the HART transmitter. Because the intelligent transmitter is between the input pressure source and the generated 4-20ma current signal, in addition to machinery and circuit, there is also the operation of microprocessing chip on the input data.So there is a difference between tuning and conventional methods.;Calibration is: "set the range", "reset the range", "fine tuning".The "setting range" operation mainly completes the configuration work through the digital setting of lrv.urv, while the "resetting range" operation requires the transmitter to be connected to the standard pressure source and guided by a series of instructions. The transmitter directly senses the actual pressure and sets the value.The initial and final setting of the range depends directly on the actual pressure input value.However, you should note that although the analog output of the transmitter has the correct relationship with the input value used, the digital reading of the process value will show a slightly different value, which can be calibrated by fine-tuning the item.Since each part needs both separate adjustment and joint adjustment, the actual calibration can be carried out according to the following steps:
Make A 4-20ma fine tuning first to correct the D/A converter inside the transmitter. Since it does not involve sensing components, no external pressure signal source is required.
Make another whole-process fine-tuning to make 4-20ma and digital reading consistent with the pressure signal actually applied, so the pressure signal source is required.
3. At last, the range is redetermined, and the simulated output of 4-20ma is made consistent with the external pressure signal source through adjustment, and its function is exactly the same as the zero (Z) and range (R) switches on the transmitter shell.
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