Calibration of Diaphragm Pressure Gauges

In order to solve the maintenance problem of diaphragm pressure gauge, after many experiments, the company has made a set of equipment for filling silicone oil into the spring tube by using the existing device, and summarized the oil filling method. The specific methods are as follows:

1. Make special calibration tools for the diaphragm pressure gauges

The connecting thread of the head of the diaphragm pressure gauge used is standard thread. In addition, each diaphragm pressure gauge is equipped with a connecting flange. Therefore, to calibrate the diaphragm pressure gauge, it is necessary to make a special supporting flange for calibration.

2. Calibration process of diaphragm pressure gauges

1) First remove the head part of the diaphragm pressure gauge from the flange. Then connect the pressure gauge and calibrator together, and calibrate and adjust it with the pressure calibrator according to the calibration method of ordinary pressure gauge. Clean the diaphragm flange and fill it with oil through a funnel;

2) At this time, transformer oil may be brought into the spring tube. Hold the gauge by hand and shake it a few times to clean the transformer oil in the spring tube. Put the head of pressure gauge with the spring tube downward on the vacuum gauge calibration table;

3) The two-way valve is set to the "on" position, and the three-way switching valves A, B and C are not connected. Use the sucking pump to pump air, and the vacuum indicated by the standard vacuum gauge is greater than 0.93pa, the greater the better. If the vacuum degree is less than 0.93pa, the air extraction system is not well sealed, and there will be small bubbles after filling  the spring tube with oil, which will affect the accuracy. First, set the two-way valve to the "off" position, and then flip the three-way switching valve to make A, C connected, except B, and silicone oil is filled into the gauge. In order to make the tiny bubbles left in the spring tube escape due to people during oil filling and unfinished air extraction, it is best to stop for 10 minutes and then remove the pressure gauge;

4) Place the head of the spring tube pressure gauge vertically upward to prevent oil leakage. After filling, wrap PTFE sealing tape around the joint, quickly twist and join the head of the pressure gauge and the flange capsule together and fasten it. Since the silicone oil sealed in the gauge is pressurized during tightening, the zero point of the pressure gauge is raised. Open the vent hole on the capsule with an allen wrench to release the residual pressure in the capsule, and observe the pointer of the meter to make it indicate at the zero scale mark. In the process of pressurization, when the pointer of the measured gauge points to the first large scale line and is completely consistent with the pressure of the standard gauge, tighten the screw thread;

5) Finally, verify the zero point and range. Connect the diaphragm pressure gauges and the manufactured calibration with flange, and install the assembled gauge on the pressure calibrator for calibration to make it qualified.

In the above steps, the most important thing is to exhaust the air, and no small bubbles can be left in the oil, otherwise the instrument error is large, and it’s not good to return to zero for pointer, and the accuracy is greatly reduced. Check the accuracy of the original gauge in the manual, and the accuracy of the gauge repaired by the above method will be qualified.

According to the experience of our company, when the diaphragm pressure gauge is installed in a place with large vibration, it is best to fill the case with shockproof silicone oil, so as to ensure that the diaphragm pressure gauge has a long operation cycle.