Essential mechanical test equipment list for calibration

Testing your measurement equipment regularly to ensure it is calibrated and accurate ensures you maintain quality standards and reduce operational downtime. This article will help you create your essential mechanical test equipment list for calibration, ensuring you have access to correctly functioning devices when you need them.

What is calibration?

Using test and measurement equipment effectively relies on your devices providing accurate readings. Calibration is the process where equipment is comprehensively tested against a known quantity. The accuracy of its readings is measured, and adjustments made where necessary. To maintain accuracy over time, each device must be regularly calibrated at set intervals. This periodic calibration is required because of measurement drift.

When establishing calibration intervals, the vulnerability of each instrument to the effects of drift should be considered, and a critical mechanical test equipment list generated. This list should include the most susceptible items or where out of tolerance readings would pose a particular risk.

Extra measures should then be taken to identify measurement drift before it moves the readings of the instrument beyond what is deemed acceptable.

What is calibration drift in mechanical test equipment?

Drift is the tendency for equipment to deviate from its calibrated state. All kinds of test equipment are susceptible, and the drift can be characterised as either short or long-term. An example of short-term drift would be a Vernier calliper which has travelled in an aircraft hold. The low temperature would cause the scale to contract, introducing a temporary element of inaccuracy. The instrument is likely to return to accurate operation under ambient conditions.

Long-term drift is a permanent condition possibly caused by damage or wear-and-tear. For example, the weakening of the compression spring in a torque wrench. Recalibration or repair would be necessary to resolve this.

Drift can take several different forms. Offset drift is where equipment will always read high or low by the same amount throughout its measurement range. When the accuracy of a device reduces in proportion with the measured quantity, this is known as span drift. If the instrument measures accurately apart from in a certain spot in its range, this is known as zone drift. During the calibration process, an instrument could be identified as having one or all of these issues.

Causes of mechanical calibration drift

All mechanical test equipment will inevitably display measurement drift over its service life. Metal components such as springs become less ductile as they age. Plastics will become more brittle. Light corrosion or hardening of internal grease can introduce friction to moving parts. These will all introduce a gradual shift in the quality of the readings produced.

External factors such as physical shocks from improper storage or use can contribute significantly to errors. As will using test equipment beyond rated span or range or failing to complete preventative maintenance such as pre-use checks, cleaning and lubrication.

Regular calibration by an accredited lab will identify and resolve measurement drift. Quality Management Standard ISO9001:2015 Section 7.1.5 requires that the resources needed to generate accurate results are established and provided. Where instruments are exposed regularly to the causes of measurement drift, the intervals between calibrations should be established specifically to ensure they always read accurately in service.

6 items for your critical mechanical test equipment list

1. Torque Wrenches. These can be mechanical click-off or digital types, or even bolting guns with adjustable torque settings. It is very likely that they will be handed roughly in service, making regular calibration essential.
2. Weighing Scales. Small capacity scales are easy to overload. Industrial warehouse scales may have heavy pallets dropped on them or be bumped by forklift trucks. Overloads and impacts are known causes of mechanical measurement drift.
3. Vernier Gauges and Micrometers. If these are not stored in their protective case, their condition will soon start to degrade. Especially if stored and transported alongside other tools. As these items are often used for QA checks, accurate readings are crucial.
4. Pressure Gauges. Sudden increases in pressure can have a detrimental effect on accuracy over time. Gauges mounted on flexible hoses are also at additional risk of impact damage. These are often used in safety critical applications.
5. Vibration Probes. Vibration causes damage to rotating plant machinery. As the condition monitoring probes are exposed to the same harmful environment, they require regular testing. Especially as they are typically used to monitor critical equipment.
6. Flow Meters. Whether metering a gas or fluid, the potential for contamination or foreign object ingestion is always present. Items with moving parts such as impellers are also susceptible to wear and tear.

Calibration experts for your critical equipment

At DM Systems & Test, we have extensive experience with calibrating all kinds of mechanical test equipment. We have historic calibration records for instruments from a wide variety of manufacturers going back decades. If you bring an instrument to us, we’ll have seen it or something very similar before. We’ll know how soon it is likely to need another calibration check, and we can schedule this for you.

We also appreciate that our calibration services represent a cost to you, as is having your equipment out of service while we do the testing. We can evaluate the measurement drift we identify at each calibration check and use this to identify calibration intervals that will keep your instruments reading accurately, while minimising the cost and inconvenience of downtime.

For more information on our UKAS accreditation, or to find out which of our mechanical calibration services are UKAS accredited, get in touch. We have a team of experts who are available to advise and recommend which level of calibration is most suitable for your application or industry sector.