Issues with on-site pressure testing after negative migration of the transmitter
Thread Content
A differential pressure transmitter for measuring liquid level in a two-chamber balanced container, with a range of -8 to 0 kPa after migration. During major repairs, pressure testing is required. Which of the following methods is used on-site for pressure testing and calibration? Talk about the advantages and disadvantages. 1. Change the range to 0–8 KPa; expose both the positive and negative sides to atmospheric pressure, open the balance valve, zero the scale, and then perform pressure testing on the positive pressure side. After completion, change the range to -8～0 kPa. 2. Pressurization adjustment on the negative pressure side. The system is connected to the atmosphere under both positive and negative pressure; the balance valve is opened, zeroed, and then pressure testing is carried out on the negative pressure side. There’s no need to keep changing the range back and forth. 3. Positive pressure side suction and negative pressure adjustment. The system is connected to the atmosphere under both positive and negative pressure; the balance valve is opened, zeroed, and then negative pressure is applied on the positive pressure side for verification. No need to adjust the range back and forth
2 and 3 are the best options; no need to change the range after verification, which avoids errors that can occur as a result of changing the range
From a practical perspective, methods 2 and 3 indeed avoid the risk of errors caused by repeated range adjustments. Two additional points of experience for reference: When adjusting the pressure on the negative-pressure side, it is important to pay attention to the sealing quality of the connections of the pressure pump. In our field operations, we have encountered situations where slight leaks in the threads on the negative-pressure side caused the calibration data to become inaccurate. If negative pressure is to be applied, it is advisable to first determine the transmitter’s tolerance for negative pressures; in some older models, the diaphragm box may experience slight deformation when subjected to a continuous negative pressure of -8 kPa. The choice of method should be determined based on the model of the equipment on site and the capabilities of the calibration tools available.