What you need to know about Pressure Gauge Calibration

To start off our discussion of calibration and its importance we should first start with a clear definition.  Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible and with a second device.  The device with the known or assigned accuracy is called the standard.  The second device is the unit under test.  There are a couple of different methods of collecting calibration data; Cardinal Point Calibration and, Nominal Point Calibration.  For the purposes of Pressure Gauge Calibration, Cardinal Point Calibration is one where a specific value is set on either the test or the reference instruments.  Nominal Point Calibration is one where a value is set near the target value.  The exact value that is set is not as important as knowing what that value is.

Now that we have a definition of Calibration to work from, why do you need to keep your gauges calibrated and what determines the frequency?  Having a gauge that is regularly calibrated is essential to ensure that you are getting accurate readings when using the gauge.  Calibration frequency can be determined by a number of factors.  Often the manufacturer of the device will have a suggested calibration interval.  The interval is determined by factory testing based on how long the gauge is expected to stay in tolerance.  While this can be helpful, the manufacturers recommended interval should not be your only deciding factor.  Your company may have a Quality Assurance (QA) program which specifies that devices be calibrated on a more frequent or less frequent basis.  Keeping good records and data on how your instruments react to their working conditions over time will help you to determine a good calibration frequency for your specific needs.  Field instruments may require more frequent calibration when compared to lab instruments due to environmental influences.  Humidity, contamination, temperature, vibration or shock can all influence your gauge’s calibration status.

Where to have your gauge calibrated is another important consideration to take into account.  You need to ask some of the following questions to ensure you are getting what you want.  Does your QA program specify that you need an accredited lab to do your calibration, what about ISO?  If so, do they have all the proper documentation to support their accreditation?  Do you trust the lab that is doing the calibrations?  It takes more than simply acquiring the standards to take good measurements.  Does the lab technician have training, procedures and a stable environment in which to perform the calibrations?  Are their standards traceable to national standards (NIST) and kept in tolerance?  These are just a few of the questions to keep in mind when researching your lab.

Now that you are familiar with why, when and where to get your gauge calibrated lets look at a couple of things you can do to keep your gauge working well.  Many of the devices being used today are digital.  These types of devices may have software upgrades that can be downloaded on the manufacturer’s website and updated by the user.  Keeping your device updated will help keep your device working in top shape.  Another thing to keep in mind is never try to open or do any internal work on your gauges.  Calibration or warranty of gauges may be void if the device is opened internally.  Always check with the manufacturer or your calibration facility before opening up the instrument.  Generally, the only reason any part of the gauge should need to be opened is to change the batteries.  Opening of the gauge by untrained personnel may compromise the device and can lead to very costly repairs, sometimes costing as much as or more than a new gauge.  Finally, keeping debris out of the gauge, using the correct fittings, careful handling and proper storage will all go a long way to protecting the device and maintaining calibration integrity.

To conclude our discussion of gauge calibration we have looked at what calibration is and why it is important.  We have also discussed frequency and ensuring you have a reputable lab.  By taking all the variables we discussed into account, you should be well on your way to keeping your gauges reading accurately.