Sending equipment in for calibration can sometimes be a costly and inconvenient procedure, but regular calibration is essential to maintain accuracy and reliability of your instruments.

Instrument manufacturers are continually developing new and innovative products. For instance testo has just launched a new range of Smart probes for HVAC/R contractors. The new range measures parameters such as temperature, pressure and airflow. Testo Smart Probes are supported by easy to download Apps which make the applications considerably easier thanks to a Bluetooth connection to a smartphone or tablet.

Despite the fact technology is continuously advancing, the price of these exciting new products is actually coming down. With lower pricing in mind, one of the more frequent questions contractors ask is “why is the cost of calibration high compared to the price of the instrument?”

We spoke with Service and Calibration expert Paul Jordan to help further understand the options available and help users to make informed choices about calibration.

Testo’s Calibration Director Paul Jordan

Levels of calibration

Good quality instrument manufacturers such as Testo deliver new instruments with a document called a Protocol or Certificate of Conformity (C of C). For some customers and applications this is sufficient. It states that the instrument was checked and is within stated tolerance limits. The results are fixed and cannot be adapted to suit a customers’ individual requirement. The protocol also states, “Measurements are traceable to a National Standard”.

Sometimes customers require new equipment to be delivered with a calibration certificate rather than a C of C. More often organisations require their instrumentation to be calibrated periodically. In both cases Testo offers two recognised standards of calibration:

ISO Calibration certificates – Testo supply these, when requested, from its own accredited calibration laboratory in the UK. These certificates are fully traceable to a national and or International standard(s) and the route of traceability is transparent as Testo state exactly what reference equipment was used to perform the calibration on the certificate. The customer can select calibration points to satisfy their requirement and a measurement uncertainty is documented.

UKAS calibration certificates – UKAS calibration certificates are another level up from the ISO certificates. Any accredited calibration laboratory, not just in the UK, is accredited against the international standard ISO17025:2005 “General requirements for the competence of testing and calibration laboratories.” In order to achieve accreditation to this standard a laboratory is assessed by an accreditation body; in the UK this is UKAS. Audits can be rigorous and it is because Testo conforms to the standard we can provide assurances that a calibration certificate we issue is of a high level both from a technical and qualitative aspect.

Calibration Points

The simplest temperature calibration, for instance, may involve the instrument being checked against a single reference temperature. However, this does not check that the instrument is accurate across the range, therefore most calibrations are carried out over a range of temperatures.

Most HVAC/R standards are vague regarding the level of calibration required or the measurement points. Generally, the standard requires that the instrument is calibrated “to the manufacturers recommendation” or similar. Organisations need to consider whether a minimal calibration will suffice or if the additional confidence afforded by a more detailed calibration is needed.

One of testo’s newly relaesed ‘Smart Probes’ being calibrated

Costs

So, back to the original question “why is calibration expensive relative to the price of the new generation of instruments?”

The answer to this question is not simple as there are different factors which contribute but essentially the process of delivering a technically competent calibration has inherent costs associated with it. In other words the cost of the instrument is not directly related to the cost of the calibration, and as already explained earlier it depends on the level of calibration chosen. Costs which contribute can vary such as reference equipment purchase price, other testing apparatus required such as a wind tunnel, on-going equipment maintenance including re-calibration, maintaining good quality processes and of course manpower.

These costs exist whether calibrating a high end reference instrument or a typical budget instrument and therefore the question of cost is more a consideration for the instrument and its application rather than the calibration. If you need to make a measurement, particularly in industries where you need to demonstrate compliance or have to comply with an internal or external quality standard, then calibration should be important. This is not only a consideration when purchasing a new instrument but also for subsequent calibration at a defined period thereafter.

Any laboratory offering calibration services will need to adopt robust processes. Any credible laboratory, and particularly one which is accredited to ISO17025 such as Testo’s calibration laboratory, will spend time maintaining the calibration processes and accreditation. This can include initial analysis, measurement uncertainty calculation, and ongoing performance checks and in some cases inter laboratory comparisons (checks against other laboratories reference equipment) which further enhance confidence in the Laboratories ability to produce meaningful measurements. Of course, these activities also require analysis and supporting documentation which is required to demonstrate the laboratories competence during an audit.

Measurement Uncertainty

One key element of any calibration is the laboratories ability to assign a measurement uncertainty to any measurement performed. This is essential as absolute accuracy does not exist, and therefore any measurement will have a degree of uncertainty. The amount of measurement uncertainty can vary and many factors can contribute or effect this key element depending on the type calibration being carried out.

If the measurement uncertainty is not documented on a calibration certificate the measurement cannot be quantified and therefore the measurements can be considered meaningless. Measurement uncertainty is commonly overlooked when comparing calibration prices between one laboratory and another and quite often is the reason a calibration can be cheap. If calibration is important to you, and to your client, there is a responsibility to ensure the calibration you purchase will stand up to the rigours of any inspection, audit or possible HSE investigation.

Accuracy counts



So the calibration question needs to be considered not just in the context of cost but in what standards are you trying to meet and how important is it measurements I make for my customers are accurate. Testo continues to optimise processes and look for ways to reduce the price of calibration services without compromising quality. As a diligent laboratory accredited by UKAS to ISO17025 you can be assured when a customer sends their instrument to Testo for calibration, regardless of the initial cost of the instrument, they can be confident in the service we provide.

For more information on testo’s calibration services or any testo products please visit our website: www.testolimited.com or give us a call on 01420 544433