Pressure Gauge Calibration Explained

Pressure gauges are the workhorses of Singapore industry — sitting on chemical reactors in Jurong Island, hydraulic test rigs in Seletar, compressed-air lines in every factory, and fire suppression panels in every building on the island. They're cheap, familiar, and the first instrument most people stop paying attention to. They're also, consistently, the most commonly out-of-spec instrument on any given site. This is what a proper pressure gauge calibration looks like, and what to watch for when yours come back from the lab.

Types of Pressure Gauges You'll See

The term "pressure gauge" covers several very different instruments. The calibration approach depends on which type you have.

Bourdon tube gauges (analogue dial)

The traditional round dial with a mechanical pointer. Inside is a curved metal tube that straightens slightly as pressure increases, moving the pointer via a linkage. They're robust, cheap, and the most common pressure gauge on any industrial site. They're also the most prone to drift — the Bourdon tube work-hardens over time, especially under pulsating loads.

Diaphragm and capsule gauges

Used for lower pressures, corrosive media, or viscous fluids. A flexible diaphragm deflects with pressure and the movement is transmitted to a pointer or transducer. More forgiving of contamination, less prone to shock damage.

Digital pressure gauges and transducers

Piezo-resistive or capacitive sensors with digital display or 4–20 mA output. Used on test benches, calibration rigs, and any application requiring data logging. Generally more stable than analogue gauges, but still require calibration — drift happens more slowly but affects every reading.

Vacuum gauges

Measure pressure below atmospheric, down to about –1 bar gauge. Calibration requires a reference vacuum source and traceable low-pressure standards.

What Calibration Actually Involves

An accredited pressure gauge calibration follows a documented procedure, typically derived from standards such as EURAMET cg-17 or manufacturer guidance. The core steps are:

1. Visual and functional check — inspect for damage, zero drift with pressure released, pointer action, dial legibility.
2. Reference standard setup — connect the gauge to a calibrated pressure source. For higher accuracy work, the reference is a deadweight tester (a primary standard); for general work, a calibrated digital master gauge is acceptable.
3. Ascending and descending points — apply pressure at a series of calibration points (typically 0, 20, 40, 60, 80, 100% of range, then back down). Record the indicated value at each point.
4. Hysteresis check — compare ascending and descending readings at the same pressure. A large difference indicates mechanical friction or Bourdon fatigue.
5. Repeatability — repeat the cycle to check whether the gauge gives consistent readings.
6. Results and uncertainty — tabulate deviations from the reference, calculate measurement uncertainty per the GUM, and issue a certificate with as-found and (if adjusted) as-left values.

Accuracy Classes You'll See on Data Sheets

Pressure gauges are commonly rated by accuracy class, expressed as a percentage of full scale. The most common classes (per EN 837-1 for Bourdon gauges):

• Class 0.1, 0.25: Test and reference-grade gauges for laboratory use.
• Class 0.6, 1.0: High-quality industrial gauges, often used for critical process measurement.
• Class 1.6: General industrial use, the most common class on shop floors.
• Class 2.5, 4.0: Lower precision, commonly seen on utility and compressed-air gauges.

The accuracy class tells you the maximum permissible error as a percentage of full scale. A Class 1.6 gauge with a 10 bar range can be up to ±0.16 bar off at any point. If your process requires ±0.05 bar resolution at 2 bar, a Class 1.6 gauge will never give you that — no amount of calibration fixes an inadequate accuracy class.

Common Failure Modes

• Zero offset — gauge doesn't return to zero when pressure is released. Usually mechanical (bent pointer, sticking movement) or aging Bourdon tube.
• Linear span error — gauge reads consistently high or low across the range. Often correctable by adjusting the movement.
• Non-linearity — gauge reads accurately at some points but not others. Indicates mechanical wear in the linkage or permanent deformation.
• Hysteresis — different readings on ascending vs descending pressure. Mechanical friction or Bourdon fatigue.
• Erratic needle movement — usually a sticky movement, dirty internals, or failing bearing. Calibration will not fix this; the gauge needs service or replacement.

Installed Pressure Gauges and On-Site Calibration

Removing a pressure gauge from a live process is rarely trivial — it means shutting down, draining, isolating, and then leak-testing after reinstallation. For fixed gauges on active plant, on-site calibration is often the practical choice. A qualified technician brings a calibrated pressure source, connects in parallel or via an isolating manifold, and runs the full calibration without removing the gauge from service.

UT Metrology's Pressure Calibration Capability

Our SAC-SINGLAS accredited scope covers pressure and vacuum calibration from full vacuum (–1 bar gauge) up to 700 bar, covering the range of most industrial gauges, transmitters, and test equipment used in Singapore. We perform lab calibrations at our Bukit Batok facility and on-site calibrations across Singapore, using calibrated reference standards traceable to SI units. View our mechanical calibration page or request a quote with your gauge list and we will confirm scope and turnaround.