If you work to ISO 9001: 2015 and/ or ISO 17025:2017 standards, it’s imperative that you establish a calibration programme that ensures the validity of the results given by your weighing equipment.  While ISO standards outline the need for calibrations, no prescribed guidance is provided to determine calibration frequency.  To safeguard the accuracy of your equipment, we look at key considerations to help you define the best frequency for your process, equipment and application.

1. Manufacturers’ recommendations

Manufacturers’ guidance is a good place to start.  Located within the user manual, the recommended frequency will provide a useful baseline of calibration frequency.  However, if your equipment is critical to your process, you may need to follow a risk-based methodology (see 2) to determine a bespoke frequency.

2. Risk-based methodology

As the accuracy of weighing equipment becomes less reliable over time, a risk-based methodology is commonly used to determine calibration frequency and considers the following points:

a. Criticality of results

If you have very tight tolerances or need a very small Uncertainty of Measurement (UoM), this may determine the need for shorter calibration intervals. This will help you to identify any deviations against your tolerances and keep your UoM in line with your Quality Management System (QMS).

b. Frequency of use

Equipment in heavy use will be subject to greater wear and tear and may benefit from more frequent calibrations to identify drifts.  Capturing trends in drifts over time will identify whether calibrations should be completed in longer or shorter cycles based on your specific usage and application.  For instance, the extent of drift in the results from one calibration to the next may show a shorter calibration interval is required to ensure that the equipment stays within your required tolerances.

c. Environmental factors

Accuracy can be affected if equipment such as balances and scales are located in non-sterile areas, unstable environments or subject to temperature extremities. More frequent calibrations should be performed in these instances to ensure weighing results are not impacted.

3. Statutory or regulatory requirements

If you operate within statutory or regulatory requirements, you may need to implement a more stringent programme of calibrations to ensure compliance.  While ISO standards don’t offer specific guidance on how often to calibrate, internationally recognised guidelines are available to help you to determine suitable intervals for your purposes.  By following the published guidelines below, you can be sure you’re adopting the highest standards for good measurement practice.

GMP 11: Good Measurement Practice for Assignment and Adjustment of Calibration Intervals for Laboratory Standards

ILAC-G24:2007/OIML D10:2007, Guidelines for the determination of calibration intervals of measuring instruments

4. Internal and external QMS stipulations

The calibration frequency of weighing equipment may be determined by your in-house criteria and/ or your customers’ QMS.  While you may deem your weighing process to be less critical, weighing inaccuracies may have a significant impact on downstream customers.  To strike the correct balance, any contractual obligations around customers’ calibration intervals should be considered alongside your in-house requirements.

5. Transportation or accidental damage

If your equipment has been in transit or has been damaged, recalibrating the equipment will help to ensure your results remain accurate and reliable before your next scheduled calibration.  This action is especially critical for higher resolution weighing equipment, which is more sensitive to movement and knocks.

Is there a definitive answer?

There’s no one-size-fits-all solution to how often you should calibrate.  If you have a range of equipment operating under varying conditions, you may also need to implement simultaneous schedules.  By taking the factors above into your frequency assessment, you can determine a customised calibration programme to optimise the accuracy of your weighing results.

For help to identify the best calibration frequency, contact our specialist engineers who can complete a comprehensive assessment and develop a bespoke programme of UKAS and/ or traceable calibrations for your needs.  This will help to reduce the risks of downtime, non-compliance and recalls.  If your business needs change, our engineers are also on hand to reassess your schedule.