Inspec Insights

Interim Checks, Another Way to Assure Quality


What are they?
Interim Checks are generally short “tests” of equipment to ensure they are still functioning properly.

Why do them?
Since calibrations of larger equipment such as vision systems, CMMs, X-Ray/CT are usually only done annually, there is a possibility that something may have happened to the equipment since the last calibration and it could be giving erroneous results.  If it is not discovered until many months after the problem occurred there could be a very large liability stretching all the way back to the last calibration (since you may not know when the problem first arose).  By performing Interim Checks, you are verifying that at that moment the system is functioning properly (if it isn’t, then the system needs to be repaired and recalibrated).  Any problem will only have happened since the last passing interim check, reducing the period of liability.

 When to do them?
That is a judgement call on your part.  The more frequent you do them, the shorter the period of liability but also the less time used for actual inspection/measurement work.  The frequency is usually determined based on:

  • The liability encountered for erroneous information
    • If there is a high liability in customer safety or the product use, they should be done more frequently
    • If there is minimal impact the period may be extended
  • The amount of time the equipment has been in use
    • If the equipment is subject to excessive wear, the frequency should be increased
    • If there is negligible wear the frequency can be reduced
  • The time period since the last Interim Check, a fixed amount of time is set, such as:
    • Every 10 days of use or
    • Each month when the equipment is not being used

How to do them?
Usually, based on the type of measurements done, there will be an artifact (some fixed piece of equipment or part that is used exclusively for the Interim Check) which will be measured to verify that the results are consistent compared to the prior results (it should be checked right after a calibration, when you know the measurement system is functioning properly). Examples:

For a CMM it could be a ballbar measured at different angles, comparing the lengths at the different angles and compared to the initial calibrated length

  cmm artifact

 For a Vision System, it could be a glass plate with various sized shapes, lines with a scale

  glass plate

For an X-ray system it could be uniform disks of various densities with specific shaped plugs within the disk to measure uniformity of the field and recognition of the shapes and sizes

xray artifact

Who does them?
Normally they are performed by the technicians that use the equipment.  If the Quality team is skilled in the use of the equipment, it could be a quality technician who performs the interim checks.  They can also be completed by a calibration house such as Inspec.

So to keep your accuracy high and your liability low you’ll want to incorporate interim checks into your laboratory procedures.  Inspec can help you set up an Interim Check schedule or we can come and perform them for you, contact us today to discuss how we can help you.

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