A deadweight tester is a proven method of pressure calibration that is usually chosen for bench applications when accuracy and reliability are the top requirements. Calibrations are performed at the bench for convenience and to maintain reference conditions. The bench is a convenient location to clean, inspect, calibrate and repair with all the necessary equipment available. Reference conditions are necessary to achieve the reference accuracy of the device under test and the calibration standards. Reference accuracy may be required to maintain the necessary test uncertainty ratios (TUR).
To perform the test:
- The pressure gauge should be mounted in the same orientation (vertical or horizontal) as in the process.
- Measurement points should be distributed uniformly over the calibration range.
- Calibrated weights are placed on the instrument corresponding to the measurement points.
- Pressure is added with an internal pump or screw press until the piston holding the weights begins to float.
- The piston and weight are spun by hand to minimize friction.
- While the piston is floating the reading on the device under test is compared to the pressure corresponding to the sum of the selected weights.
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