Measuring equipment management checklist: how to be ready for the audit

Scales and weights come up in almost every quality audit. Whether it concerns ISO 9001, HACCP, BRC, IFS or GMP: the auditor wants to see that your measuring equipment is reliable and that you can demonstrate it. The measuring instrument itself is rarely the problem. Usually things go wrong in the administration around it.

With this checklist you can go through your measuring equipment management in advance. The points are based on what we encounter at customers in practice. Calibration is not a legal requirement, but the standards mentioned do ask for calibrated measuring equipment at defined intervals, traceable to national standards. For the periodic calibration of your weighing equipment, see scale calibration.

Register and identification

Everything starts with a complete overview. An auditor often picks a random scale on the shop floor and asks you to find it in the records, or the other way round.

1. Is there an up-to-date measuring equipment register? With, for each instrument, a unique number, description, make, model, serial number, location, range and readability.
2. Is the application recorded? What is the instrument used for and which tolerance applies to it? That later determines how the certificate is assessed.
3. Are all relevant measuring instruments included? Including check weights, spare scales and instruments that are only used occasionally.
4. Is each instrument physically identifiable? With a label carrying the number from the register, preferably supplemented with the calibration status or the date of the next calibration.
5. Are instruments that must not be used marked as such? For example with a label out of service or indicative only.
6. Is it indicated which scales must be legally verified? For selling by weight or pre-packaging, a legal requirement applies in addition to your quality requirement.

A tip: keep check weights in a case with the same number on the case and on the certificate. Loose weights without identification are difficult to account for at an audit. Suitable storage can be found under cases and accessories.

Intervals and justification

1. Does each instrument have a defined calibration interval?
2. Is the interval justified? Consider intensity of use, environment, the importance of the measurement and the results of previous calibrations. Annually is a common starting point.
3. Is the interval adjusted? If a scale consistently stays well within tolerance, a longer interval may be justified. If it regularly deviates, a shorter interval is needed.
4. Is there a schedule and is it met? An expired calibration date is, in our experience, one of the most frequent audit findings.
5. Is it recorded what happens when a date is exceeded? For example temporary additional interim checks or blocking the instrument.

More about choosing and adjusting intervals in how often should a scale be calibrated.

Certificates and assessment

1. Is the most recent certificate for each instrument readily available?
2. Is the identification correct? The serial number or your own number on the certificate matches the register.
3. Does the certificate contain measurement results and measurement uncertainty? Without measurement uncertainty it is not a calibration certificate.
4. Is traceability to national standards stated?
5. Has the certificate been assessed? Against the tolerance for the application, with date, name and conclusion: conforms or does not conform.
6. Have the results before and after adjustment been kept? You need the results before adjustment for an impact analysis.

How to read and assess the results is explained in calibration certificate explained.

Interim checks

Between two calibrations a scale can drift, for example after a fall, overload or relocation. Interim checks reduce the period over which you are left in uncertainty when a deviation is found.

1. Is it recorded which instruments are checked in the interim, how often and by whom?
2. Is the method described? For example a check with a calibrated weight at a load that matches the use, possibly supplemented with a corner load check.
3. Is there an action limit? What is permitted and what does the employee do when the limit is exceeded?
4. Are the check weights themselves calibrated and suitable? As a rule of thumb, the error of the weight is at most one third of the permissible error of the scale at that load.
5. Are the results recorded and reviewed periodically? A trend is often visible before a limit is exceeded.

A practical approach can be found in checking your scale between calibrations.

Nonconformities and impact analysis

For an auditor the question is often not whether there are nonconformities, but what you do about them. ISO 9001 explicitly requires you to assess whether previous measurement results have been affected when an instrument is found not to conform. Suppose that at the annual calibration a scale in the packaging line turns out to read too high, outside your tolerance. What now?

1. Block the instrument and mark it as rejected until it has been adjusted or repaired and recalibrated.
2. Determine the period. Since when could the deviation have existed? Look at the last good calibration and the interim checks.
3. Determine what was weighed in that period. Which products, batches or analyses were determined with this instrument?
4. Assess the consequences. Is the deviation relevant to the product specification, food safety, legal requirements or agreements with customers? In the example: do packages contain less product than stated?
5. Decide on measures, such as reassessing released batches or informing customers, and record the reasoning.
6. Find the cause and prevent recurrence, for example with a shorter interval, additional interim checks or a better set-up.
7. Close the nonconformity demonstrably in your nonconformity records.

If the scale is legally verified and a seal has to be broken for the repair or adjustment, re-verification is also required before it is used again for legal applications.

Responsibilities and traceability

1. Is there someone with overall responsibility for measuring equipment management? And is there a deputy in case of absence?
2. Is it clear who assesses certificates and who releases or blocks instruments?
3. Have the employees who carry out interim checks been instructed? And is that recorded?
4. Has the calibration laboratory been assessed as a supplier? With a justification of why this laboratory is suitable for your measuring equipment.
5. Has traceability been demonstrated? The certificate states the references used and their traceability to national standards.
6. Do you know whether a customer or sector requires an accredited certificate? The difference is explained in ISO 9001, ISO 17025 and traceability.

How MASSLAB helps you

MASSLAB calibrates scales of all makes according to EURAMET cg-18 and weights in classes F1 to M3, on site or in our laboratory. Our certificates are traceable to national standards and state the measurement uncertainty. In our customer portal you will find the certificates and the schedule, which makes keeping track of intervals and preparing for an audit easier. For periodic maintenance of your weighing equipment, see maintenance contracts. If a legally verified scale has to be re-verified after repair, we can do so as a Recognised Verifier (Erkend Keurder) under the Dutch Metrology Act, after checking whether we are permitted to verify that instrument.