Pressure gauges are used in process control, HVAC, hydraulics, and industrial systems. Calibration compares the gauge reading to a reference standard such as a deadweight tester or digital pressure calibrator. Accurate pressure measurement is critical for safety and process quality.
Inspect the gauge for cracked glass, bent pointer, leaking connections, or corrosion. Verify the pointer rests at zero (or the designated rest position) with no pressure applied. Record the as-found zero reading.
Connect the gauge to the reference standard using appropriate fittings. Ensure the system is leak-free. If using a deadweight tester, level the instrument and verify the piston rotates freely.
Apply pressure at a minimum of five equally spaced points from 0% to 100% of the gauge range (e.g., 0%, 25%, 50%, 75%, 100%). At each point, allow the reading to stabilize and record the gauge indication and the reference value.
Reduce pressure at the same five points from 100% back to 0%. Record the gauge reading at each point. The difference between ascending and descending readings at the same pressure is the hysteresis error.
Repeat the 50% test point three additional times to assess repeatability. Calculate the spread of readings at this point.
Record all ascending, descending, and repeatability data. Calculate errors and hysteresis. Apply calibration label with date and due date. If the gauge fails, tag it as out of tolerance and remove from service.
Per ASME B40.100, accuracy class determines limits. Grade A gauges allow ±0.5% of full scale in the middle half and ±1.0% in the lower and upper quarters. Grade B allows ±1.0% and ±2.0% respectively. Hysteresis must not exceed the accuracy class limit.
12 months
A deadweight tester provides the lowest uncertainty for pressure gauge calibration. Digital pressure calibrators are more portable and easier to use, and modern units have accuracy approaching that of deadweight testers for most gauge classes.
Testing in both directions measures hysteresis — the difference in readings due to internal friction in the gauge mechanism. Excessive hysteresis indicates wear or damage in the Bourdon tube or gear train and may disqualify the gauge from service.
Never apply pressure exceeding the rated range of the gauge. Overpressure can permanently deform the Bourdon tube and destroy the gauge. The maximum calibration point should be 100% of the gauge's full-scale range.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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