How often should test equipment be calibrated?

Any industry which depends on accurate measurement to deliver a precision product or service must make regular calibration of its test instruments a priority. Calibration is the process by which measurement equipment is verified against known and traceable quantities. Any faults or inaccuracies must be resolved with repairs or adjustments before a calibration certificate can be issued.

Of course, calibration does carry a cost, both in payment for the service itself and in equipment downtime. It is therefore important to establish a calibration frequency that is cost-effective but does not compromise equipment dependability.

Why is periodic calibration necessary?

All equipment is susceptible to measurement drift; the accuracy of the readings degrade with time and use. With longer periods between calibrations, the risk of significant drift increases. A small level of drift in an instrument is not necessarily an issue, but left unchecked it can gradually shift the readings out of tolerance.

If your measurement device gives inaccurate readings, the consequences could be costly:

• A product batch may have manufacturing defects and need to be discarded.
• Condition monitoring equipment could fail to detect a fault, leading to a breakdown.
• Products may have to be recalled, with impact on reputation as well as profits.

Regular calibration checks are crucial to guaranteeing the accuracy of your instruments, and the quality of the end product that depends on them.

What causes measurement drift?

Measurement drift is inherent in your test equipment. A device kept in storage after being calibrated will not necessarily display the same level of accuracy when it goes through another calibration process in 12 months. The way that you use the equipment can also have a bearing on the effects of drift.

Using the equipment Out of Range is where the device is exposed to loadings beyond those that it was designed for. Using a voltmeter rated at 600V to measure a 690V power supply could place harmful electrical stresses on the measurement circuits, introducing an element of drift.

Rough Handling is one of the major causes of measurement drift. Even if a device is intended to be used in hostile or rugged environments, it still needs to be handled properly. Violent shocks, drops or even sudden changes in temperature can all have an adverse impact on accuracy.

The Environmental Conditions in which your equipment is used can also impact its accuracy in service. This can often be short term, and the instrument may operate correctly again under normal conditions. However, exposing gauges and meters to factors such as strong magnetic fields or Radio Frequency Interference sources can induce permanent reading drift.

Deciding how often to calibrate your test equipment

How measurement devices are stored, transported and used can have a negative impact on accuracy. This should be a factor when considering the optimal period between mechanical calibration and electrical calibration checks. There is always a compromise between making sure the equipment will read accurately, while not taking it out of service without good reason.

Manufacturers issue their own guidelines on how often their equipment should be calibrated. This recommended frequency can be adjusted. Establishing the best calibration frequency for a piece of equipment will draw on additional factors. These can include experience of calibrating that specific kind of device and knowledge of the circumstances under which it is used. These are key pieces of information when determining how often it should be tested.

For example, with fixed equipment such as a laboratory dynamometer, rough handling and changes in environmental conditions are not likely to affect its accuracy. In contrast, a current clamp meter carried in a field service engineer’s toolbox is more likely to suffer bumps and shocks.

Some equipment always needs major adjustments to remain in tolerance. As a result, it may justify shorter periods between calibrations than devices typically passing calibration with no adjustment required. It may even be the case that devices requiring major adjustments are calibrated less frequently than the manufacturer recommends to reduce downtime.

Our recommendations on calibration intervals are subject to constant review to make sure they continue to best match your needs and are only implemented with your full agreement, in line with the requirements of ISO 17025:2017.

Calibration strategies by DM Systems & Test

There are other benefits to your equipment regularly passing through the hands of a skilled calibration lab such as DM Systems & Test. Our trained engineers may notice small defects such as nicks in the insulation of test leads that may have escaped the attention of the end user but could still impact on safety or accuracy. We may also be able to action after-sales items from the manufacturer, such as carrying out firmware updates.

At DM Systems & Test we have the knowledge and experience to offer optimised calibration strategies for a comprehensive range of both mechanical and electrical test equipment. We also understand the importance of keeping downtime to a minimum. Speak to us about how you use your equipment so we can set out the most efficient calibration schedule possible.

For further information on our calibration strategies, or to find out which of our services are accredited to ISO 17025:2017, contact DM Systems & Test.