Pressure Gauge Calibration: The Complete Guide — Methods, Standards, and Finding the Right Lab
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Why Pressure Gauges Require Regular Calibration
Bourdon tube pressure gauges are the most common measuring instrument in Thai factories — found in steam, hydraulic, pneumatic, and chemical systems. But their thin metal tube construction drifts over time, especially after shock, overpressure, or sustained vibration. Using a gauge showing an incorrect value in process control can range from product quality issues to serious safety hazards.
Types of Pressure Instruments and Calibration Methods
1. Bourdon Tube Pressure Gauge (Most Common)
- Typical accuracy classes: 1.0, 1.6, 2.5 (maximum error as % of full scale)
- Calibration method: Deadweight Tester or calibrated pressure calibrator — compare readings at multiple points on ascending and descending strokes
2. Pressure Transmitter / Transducer
- Converts pressure to electrical signal (4–20 mA or 0–10V)
- Much higher accuracy than Bourdon gauges (0.1% or better)
- Requires calibration of both the pressure and electrical signal sections
Standard Calibration Procedure for Pressure Gauges
- External inspection — cracks, broken glass, legible markings
- Zero check — pointer at zero before pressure is applied
- Connect to pressure standard (Deadweight Tester or reference calibrator)
- Ascending measurements — increase pressure from 0 to full scale, recording gauge readings at each point
- Descending measurements — reduce pressure from full scale back to 0 (checks hysteresis)
- Calculate error and hysteresis against class tolerance
- Issue certificate — test points, readings, reference values, errors, uncertainty, environmental conditions
Frequently Asked Questions
How often should a pressure gauge be calibrated?
No fixed rule — depends on criticality, frequency of use, and calibration history. General guidance: critical process gauges every 6 months; general-use gauges annually.
What if my gauge fails calibration?
Tag it "DO NOT USE" (red tag), remove it from service, repair/adjust, then recalibrate before returning it to use.