The electric contact pressure gauge is a crucial instrument. It displays pressure, control signals, and alarm signal output. It also performs pressure monitoring, level monitoring, and control. It not only guarantees the regular operation of the system but also ensures accuracy. Therefore, it is of great importance for the safe production of enterprises.
1. Calibration of setpoint deviations
We test and calibrate pressure gauges with the following parameters.
Measuring range: 0-0.6 MPa.
Accuracy: 1.6 class.
Dial size: 100 mm
Material: stainless steel 316
Process connection: 1/2 NPT
Due to the direct action of the electric contact pressure gauge, it can respond to the calibration process for set point deviations.
1.1 Calibration equipment
We need to use equipment that can be measured continuously as a standard. So, first, the live cold type manometer is excluded. Then, the calibration selects the annual stability of qualified 0.02 level with detection pressure switch detection function pressure calibrator as a standard.
When the electric contact pressure gauge occurs, and there is an output signal on or off, the pressure calibrator will receive the call and automatically record the pressure value at the time of the action so that it is easy for the calibrator to collect and analyze the data.
1.2 Capture logic for electrical contact pressure gauges
Based on the principle that the upper and lower limits of an electric contact pressure gauge are only connected simultaneously in a dry state, the connections can be made in the following way.
① When the pointer is located below the lower limit point, the common terminal and the lower limit point are connected. At this point, the pressure calibrator detects the state as connected.
② When the pointer is between the lower and upper limit points, the common terminal is not connected to the upper or lower limit points, and the pressure calibrator detects a disconnected state.
③ When the pointer exceeds the upper limit point, the expected end and the upper limit point are connected. At this point, the state detected by the pressure calibrator becomes connected again.
Therefore, we need to confirm the electrical contact pressure gauge’s insulation resistance between the terminals is qualified. Then, we can use one-way switch measurement without changing the line to complete the capture of the switch action, improve efficiency and save equipment input.
1.3 Checking procedure
According to the requirements of the calibration procedure, the electric contact pressure gauge has upper and lower limit settings. Therefore, the setpoint deviation of the electric contact pressure gauge should be checked by the upper limit of 50%, the index line near 75%, the lower limit of 25%, and the index line near 50%, respectively.
1.3.1 Pressure calibration
For (0~0.6) MPa electric contact pressure gauges, the 25% and 75% setpoints are not on the indexing line. The purpose of selecting the setpoint on the indexing line is to align the setpoint with the center line of the indexing line as far as possible to reduce errors caused by human factors.
1.3.2 Calibration for accuracy
To make the measurements accurate and efficient. The pressure calibrator is optimally controlled in terms of lift speed, assuming the pressure occurs automatically.
We first control the pressure at the fastest possible speed to near the set point, bring the indicator needle close to the set value, and then adjust the pressure calibrator to automatically control the pressure at a 1/10th of the indexed value.
When the pressure is at 0.002MPa/s, it slowly passes through the setpoint, records the pressure data immediately after capturing the switch action, and then controls the pressure at the fastest speed to near the next setpoint, thus automatically completing the automatic information acquisition for the pressure and rumble process.
1.3.3 Information Acquisition
Firstly, we have to use a needle toggle to toggle the lower limit point to the 0.140 MPa indexing line and then the upper limit point to the 0.300 MPa indexing line.
As the pressure calibrator captures the electrical contact action, it will automatically record the expected pressure value to get the standard pressure value at the lower limit position at 25% and the upper limit position at 50%.
We use a needle pointer to set the lower limit point to the 0.300 MPa indexing line and the upper limit point to the 0.460 MPa indexing line.
As the pressure calibrator captures the electrical contact action, it will automatically record the expected pressure value to obtain the standard pressure value with the lower limit position at 50% and the upper limit position at 75%.
2. Setpoint deviation data and analysis
The setpoint deviation test tells us that the test activity is to obtain a deviation and not an error. Then when we check the setpoint deviation, a “value” is the pressure value read on the standard (the actual value) and the “reference value” is the set pointer indication of the electric contact pressure gauge.
Setpoint deviation = actual value – setpoint value. This formula allows the setpoint deviation for lift pressure to be calculated separately. The pressure reading of the legal acts directly on the electrical contact pressure gauge when the signal output of the switch value direct reading is changed.
It is important to note that the regulations refer to two types of action: direct-acting and magnetic assisted. Therefore, their setpoint deviation allowable values are different.
3.1 Magnetically assisted electric contact pressure gauges
Magnetic contact pressure gauge has the advantages of high reliability, long life, ample contact switching power, etc. The primary verification of the magnetic adsorption, the magnetic force is too small to reduce the reliability of the contacts. Too large magnetic force may cause the connections to disconnect promptly and may cause bad results.
3.2 The role of the magnetically assisted electric contact pressure gauge
The mode of action is generally indicated on the electric contact pressure gauge. We should check carefully during the calibration to avoid misjudgment.
As a metrologist, you must follow the regulations carefully to complete the electric contact pressure gauge calibration. Suppose you encounter doubts in the verification process. In that case, we should think more and more analysis and a correct in-depth understanding of the meaning of the regulations to improve their business level continuously.