Pressure Gauge Calibration

When calibrating a pressure gauge, it is best to utilize the same media that the pressure gauge is attached to. If this is not feasible, calibration with air/gas is appropriate for low-pressure gauges, whereas liquids are safer for high-pressure gauges.

Because of the hydrostatic pressure of the medium, the difference in height between the pressure gauge calibration equipment and the pressure gauge might produce an inaccuracy during calibration. This is more common in liquid medium than in gas media. The size of the inaccuracy varies with the density of the liquid and the variation in height. If the calibration equipment and gauge cannot be placed at the same height, the effect of the height difference should be considered during calibration. A 2.5 cm (1 in) height variation allows for a pressure measurement error of around 0.02 bar (0.3 psi).

Contamination such as dirt, moisture, or oil can harm both the pressure gauge and the calibration equipment. As a result, it is critical to ensure that the media and equipment are free of contamination and do not interfere with the operation.

A leak test is required prior to calibration because any leakage in the pipe system might cause calibration problems. Pressurizing the system, allowing the pressure gauge to settle, and monitoring the pressure are all ways to do a leak test. Any decrease in pressure might indicate a leak. During calibration, the pressure loss must be kept to a minimum.

When the pressure quickly varies, the adiabatic effect can impair pressure gauge calibration accuracy. As the pressure fluctuates quickly, the temperature of the fluid inside the gauge changes, affecting the density of the fluid and hence the pressure. This might result in mistakes in the gauge’s reading, leading to erroneous calibration findings.

It is advised to utilize a pressure gauge with a high-frequency response to reduce the impacts of the adiabatic effect during calibration. Such gauges have a quicker reaction time and can correctly monitor rapid pressure changes.

Friction is caused by movement in mechanical pressure gauges. Exercising or pressurizing the system prior to calibration might help to minimize friction. This is accomplished by applying the nominal pressure, holding it for a minute, and then releasing it. Repeat two or three times more.

Because the pressure gauge is mechanical, the location of the gauge might impact the pressure measurement in the system. As a result, it is advised that the gauge be calibrated in the same place that it will be used in the real pressure measurement process. To guarantee proper installation, see the manufacturer’s instructions.

During calibration, adjust the input pressure so that the indicator needle always lands on a major scale mark instead of in between them. This makes the calibration process more convenient.

The discrepancy in pressure readings when a gauge is subjected to increased and lowering pressure is referred to as hysteresis in pressure gauge calibration. In other words, it is the difference in pressure readings between when a gauge is calibrated while rising pressure and when it is calibrated while reducing pressure. Mechanical wear, temperature variations, and gauge design can all contribute to this variance. When calibrating pressure gauges, it is critical to account for hysteresis to guarantee accurate results.

Repeatability, or the ability to generate the same reading for the same input, is one of the characteristics of an accurate pressure gauge. Calibration is required if the gauge produces different results each time. It is advised that the gauge be pressurized for three cycles before calibration.

The gauge reading may change depending on the temperature to which the procedure is subjected. Because the pressure gauge is typically calibrated at normal room temperature, changes in temperature can affect the accuracy of the pressure measurement. When calibrating, it is therefore advised to record the temperature and humidity.

Metrological traceability is critical in pressure gauge calibration because it assures that the gauge’s pressure measurements are accurate and compatible with the international system of units (SI). To establish metrological traceability in pressure gauge calibration, the gauge must be calibrated against a SI-traceable reference. The gauge is frequently compared to a recognized standard, such as a deadweight tester or a main pressure standard.

Calibration uncertainty might suggest a probable discrepancy in the calibrated value. Environmental factors, reference equipment, or operators taking the reading can all contribute to this uncertainty. It is critical to understand calibration uncertainty and separate mistake from uncertainty. Calculators for TUR (Test Uncertainty Ratio) or TAR (Test Accuracy Ratio) are one approach to be aware of linked uncertainty, albeit not all connected uncertainties are addressed. As a result, calculating the overall uncertainty of the calibration is advised to determine how successful the calibration is.

Pressure gauges must be calibrated on a regular basis to ensure the accuracy of the measurement. However, calibration requirements may vary based on the gauge’s purpose and design. Although there is no definitive answer, a typical guideline is once a year. However, it is also vital to verify for the manufacturer’s advise on the calibration time. Pressure gauges used in difficult working circumstances may necessitate more regular calibration.