Process of Pressure Sensor Calibration

Calibration is the process for adjusting the electrical signal of the pressure sensor to have a known relationship to the measured pressure. The pressure sensor must connect with the instrument for work after the calibration is completed, otherwise the required accuracy cannot be achieved and the pressure reading cannot be obtained correctly. This article will share the calibration process for pressure sensors. Each step in the process has different calibration items and technical standards.

I. The preparation before calibration for the pressure sensor

When calibrating a low-range pressure sensor, we must eliminate the effect of the liquid column difference. If there is a water column correction, we should add the correction value of the water column to the calibration. When measure medium is liquid, we should keep the geometric center of the pressure port of the pressure sensor at the same level with the lower end of the piston of the piston gauge (or the geometric center of the standard pressure tap).

• Adjustment before the pressure sensor formal calibration

Preheating according to the time specified by the manufacturer: When the manufacturer does not make provisions, it can be preheated for 15 minutes (the instrument with the reference end temperature automatic compensation is preheated for 30 minutes), and then the calibration of the pressure sensor is performed.
Verify on the main tick or integer point: Unless otherwise specified, the number of checkpoints shall be not less than 5 points including the lower limit, upper limit and common points.
The calibration starts from the lower limit value and gradually adds the input signal so that the pointer or display number is slowly stopped on the main scale value of every meter (avoiding any overshoot and return phenomenon) until the upper limit value of the range. Then gradually reduce the input signal for the down stroke verification until the lower limit value of the range. Read and record the values of the standardizer during the process (except for pressure gauge verification). The upper limit only detects the upper stroke, the lower limit only detects the down stroke, and we should record it well.
The inspected instruments without failure shall not be adjusted in any form until the adjustment is completed before the formal calibration.
For the result of the adjustment before calibration, the pressure sensor whose basic error of the indication value is less than or equal to the error allowed by the indication value, can no longer adjust the zero position and the full scale.

• Sealing inspection for the pressure sensor

1. After the pressure sensor is tightly connected to the pressure checker, balanced boost (or evacuation), and the pressure of the pressure sensor measuring chamber rises to the upper limit of measurement (or 90% of the local atmospheric pressure), then closes the isolation valve and sealed for 15min. In the last 5 minutes, the pressure value drops (or rises) must not exceed 2% of the upper limit of the measurement.
2. When the differential pressure sensor is tested for sealing, the high and low pressure chambers are connected, and the rated working pressure is added for observation.

• Static pressure error test for the differential pressure sensor

1. Differential pressure sensor must perform static pressure error test after replacing the elastic component, reassembling the mechanical component and changing the measuring range.
2. When using a piston pressure gauge as a pressure source, connect the oil and water isolation device before connecting the sensor.
3. Connect the high and low pressure chambers of the differential pressure sensor to the atmosphere and measure the lower limit of the output. Add static pressure, slowly change the atmospheric pressure to rated working pressure, after 3 minutes of stabilization, measure the lower limit of the output. Then calculate the difference between this value and the lower limit of the output when connecting atmospheric pressure. This difference is the static pressure effect, and its value should not be greater than the manufacturer's specifications.
4. If the static pressure of the sensor in actual operation is less than its rated static pressure, the static pressure error can be obtained according to the actual working static pressure test.
5. If the static pressure error exceeds the specified value, the zero point should be moved back after the pressure is released, and adjust the static pressure error again

II. The calibration project and technical standards for the pressure sensor

• Zero and full range calibration

1. When inputting the lower limit pressure signal, adjust the output current of the sensor to physical zero. When pressing to the upper limit pressure signal, adjust the output current to full range and repeat the adjustment until both meet the requirements.
2. Perform a positive or negative migration of zero based on operational requirements.
3. When the intelligent pressure sensor is first calibrated, the measured physical quantity should be applied for calibration. After that, we can use the handheld communicator for calibrations. In the case of arbitration check, a pressurization calibration is required in principle.
4. Repeat zero and full range adjustments until accuracy is met. The basic error value, return error value and output open circuit range of the sensor shall meet the requirements of the following table.
5. For the flow sensor, when the differential pressure signal is below 9%, the basic error value and the return error value are not counted.
   

Accuracy (%F.S.)	0.25	0.5	1	1.5	2.5
Basic error (%)	±0.25	±0.5	±1.0	±1.5	±2.5
Return error (%)	0.2	0.4	0.8	1.2	2
output open circuit range change (%)	0.1	0.25	0.4	0.6	1

• Detection after the calibration for the sensor
  

This detection is same as steps 1 to 3 of the adjustment before the pressure sensor calibration.

• Issue a verification report for the pressure sensor

III. The work after the pressure sensor calibration

1. Switch off the power supply of the pressure sensor and calibration instrument (No power supply meter does not have this requirement)
2. The instrument installed on site, its exposed zero, range and alarm value adjustment machines should be painted and labeled with a valid metering label.
3. Organize the entire verification record.
4. Install the pressure sensor back to its original position and restore the wiring.