This article was first published on September 12, 2022, and updated on February 19, 2025.
Not every application will require the same level of pressure gauge accuracy. For instance, the pressure of a home water system does not necessarily need to be as precise as a medical sterilizer. However, over time, even the highest quality pressure instruments can become less accurate due to factors such as wear and tear, environmental conditions, and mechanical stress.
This gradual decline in accuracy poses can lead to inefficiencies, safety risks, and compromised operations, making it critical to periodically calibrate your instruments to ensure they provide accurate readings. During my 13 years as a precision product leader at Ashcroft, I am often asked how calibration is done. Read this article to learn what is involved in pressure gauge calibration and the instruments you can use to ensure it is done correctly.
At the end of the article, you will also see links to additional resources to help deepen your knowledge on this subject and more.
What is pressure gauge calibration and why is it important?
Pressure measurements are only useful if you trust their accuracy. Calibration is the process of adjusting an instrument to ensure it operates within specified accuracy limits by comparing it to a standard with known precision and expressing this accuracy as a percentage of its span. Once an instrument is calibrated, it is restored to its original specified accuracy limits. giving you confidence that you are maintaining operational integrity and efficiency.
During the pressure gauge calibration, you need to consider several factors, including:
The relationship between calibration, accuracy, and uncertainty
Calibration is essential for ensuring accuracy and minimizing uncertainty in measurements. Here's why:
- Accuracy (or error) is a qualitative concept. It describes how closely a measurement aligns with the true value, indicating its correctness. In other words, it is the difference between the measured value and the actual value being measured. An instrument with high accuracy delivers measurements with minimal error.
Calibration improves accuracy by detecting and correcting systematic errors in an instrument. - Uncertainty is a quantification. It represents the doubt that exists about the result of any measurement. Every measurement has some level of uncertainty due to instrument limitations, environmental influences, operator errors, etc. In layman's terms, uncertainty could be expressed as “give or take.” A stick might be two meters long, give or take a centimeter or 20 cm ±1 cm, at a level of confidence of 95%.
Calibration reduces uncertainty by providing a quantified confidence level in the measurement.
Pressure gauge calibration instruments
To ensure your pressure gauge is calibrated correctly, two standards of calibration instruments are used:
1. Primary standard: This is a highly accurate standard that is not calibrated by other standards. It is defined through fundamental quantities such as length, mass, and time, and is used to calibrate other standards, known as secondary or working standards.
For example, the Aschroft® Deadweight Tester 1305D is a primary pressure standard that includes a pressure source (calibrated weights) for generating precise calibration points. It features a built-in shuttle valve that provides the method for controlling the rate of pressure increase and a micro vernier displacement valve to achieve a precision adjustment.
Figure 1: Primary standard deadweight tester.
2. Secondary standard: This standard is calibrated against a primary standard to ensure its accuracy. It serves as a reference for calibrating other instruments and must maintain a high level of precision.
Some examples of secondary standard calibration tools include:
- Ashcroft® ATE-2 Handheld Calibrator
This instrument is a great secondary standard option when precision calibration and traceability are required. Its multifunction design means it can perform precision measurements of pressure, temperature, current or voltage. The base unit includes application-specific firmware for the convenient calibration and setting of measurement and control devices, as well as logging of associated data.
Figure 2. Handheld calibrator.
- Ashcroft® Digital Test Gauges
These test gauges are highly accurate secondary standard instruments for test and measurement applications. Their full-scale total error (TEB) includes the effects of linearity, hysteresis, repeatability and temperature from 0 to 150 °F, and the silicone MEMS sensor technology provides accuracy and long-term stability demanded by test instrumentation users.
Figure 3. Digital test gauge.
- Ashcroft® A4A Precision Pressure Gauge
This analog dial pressure gauge is known for high accuracy and performance, making it a great option for use in calibration and test laboratories, as well as for precision test and measurement validation.
Figure 4. Analog precision pressure gauge.
- Ashcroft® 1082 Test Gauge
This analog instrument is known for its precision, dependability, safety and performance. It is often used for testing and validation and is constantly monitored to ensure unyielding standards and material integrity.
Figure 5. Analog test gauge.
- Ashcroft® 1084 Test Gauge
This compact test gauge is used for inspecting, testing and validating key installation points, and it is an excellent option when you need to achieve highly reliable precise pressure measurements.
Figure 6. Compact test gauge.
NOTE: When selecting an instrument to verify the calibration of a pressure gauge, the American Society of Mechanical Engineers (ASME) advises that the standard used for comparison should be at least four times more accurate. For instance, a 0 -100 psi gauge with a ±1% full span accuracy (±1.0 psi tolerance) should be checked against a pressure standard capable of measuring within ±0.25 psi or better.
When to calibrate your pressure gauge
As we stated previously, all pressure gauges lose their accuracy over time. Unfortunately, there is no set schedule for when inaccuracy of your instrument may occur. That's why it is so important to check calibration regularly. In a separate article, we discussed how the timing of calibration is set by the end user depending on both application and process parameters. However, as a general rule of thumb, we recommend that pressure instruments be checked annually.
There are some exceptions to that rule, including the following seven reasons you would want to check calibration sooner rather than later:
Ready to learn more?
Now that you know more about why calibration is important, the factors to consider in the calibration process and the instruments available to test pressure gauges, you may still have questions. Here are a few relevant articles that may interest you:
- Three Components of Pressure Gauge Calibration for Critical Processes
- How Often Should I Check the Calibration of My Pressure Gauge?
- How To Identify Your Pressure Gauge and Get the Proper Replacement
- How Does Temperature Affect Pressure Gauge Performance?
- How Do I Select the Right Pressure Gauge Range?
You can also contact us to speak with one of our industry experts to get your questions answered. In the meantime, download our guide to learn how to avoid equipment failure. 