CMM Calibration And Verification Explained By The Experts
Do you know the difference between measuring equipment calibration and verification?
The two terms are often used interchangeably between service providers, sometimes leading to confusion on what each term means. It’s certainly a question we get asked a lot here at Status. Here we take a closer look at both of these terms and explain what’s involved with each.
What Is Verification?
Verification, also known as certification, is the process of confirming whether or not a CMM is performing within its stated specifications. The probability that a measurement error is smaller than the specified maximum permissible error is indicated by a verification.
In a verification, you can specify the maximum permissible error as the largest error you are prepared to accept. However, the process does not compensate for lack of trueness or applying a correction, which is where calibration comes in.
What Is Calibration?
Calibration is the process of restoring a CMM to its original specifications. This is a completely separate service from verification and there are several factors that you need to take into consideration when thinking about calibrating your machine.
Important Considerations for Both…
- Metrology equipment needs to be accurate so it’s important to bear in mind that widening your tolerance of permissible errors when undertaking a verification can reduce the control over measurement uncertainty and quality.
- It’s vital that you understand what your CMM service provider is offering. We’re aware that some providers use the term ‘calibration’ when they mean ‘verification.’ It sounds more impressive and involved but in fact they often cannot adjust your CMM’s error map.
- You should also understand what type of service you will be receiving. Will your CMM be fully serviced with fine-tuned adjustment to bring it back in line with OEM specification as part of your routine preventive maintenance? Or will they just provide you with a certificate verifying the machine’s permissible error at the end of the process? Regardless of whether the specification has drifted or not?
- It is most important to find out how long it will take your service provider to perform the verification and calibration process too. At Status we always recommend a two day visit because our Length Bars (Gauge Blocks) need to undergo a soaking time to acclimatise to the machine’s environment – this process takes a minimum of 24 hours. Which is why it’s the first thing engineers tend to do when they start work on a customer’s machine. Unpacking the gauge block first so the soak can take place during the first 24 hours whilst carrying out other service-related work is vital for the process to take the minimum amount of time required.
- The most important thing to note in this whole process is the certification of the service provider. Is the provider a recognised calibration laboratory accredited in accordance with ISO 17025, certifying equipment to the ISO 10360 standard? These levels of accreditation are essential for ensuring competence of testing and calibration services; it’s the minimum standard you should expect from your service provider. This is standard practice for any OEM engineer that is looking to perform a full calibration, or even verification.
What about Pre-Calibration?
Pre-calibration can be performed by your metrology partner to help ensure that CMM maintenance or repairs that could affect the calibration process don’t need to take place after it. It’s a sensible cost-cutting step and we’d always recommend this to our clients. Status Service Engineers use a set checklist to ensure that the machine is really usable and suitable for calibration. This includes checking things like the cabling and connections for damage or wear, inspecting the air filtration system, running a measurement cycle to check the motor function, wiping down machine covers and the computer, reviewing firmware revision levels and updating if needed, plus much more.
Time to take a closer look at your CMM calibration and verification provider?
At Status, we have a team of calibration and maintenance specialists that deal exclusively with Coordinate Measuring Machines. We’re fully ISO and UKAS accredited and have been in business for nearly 40 years, so you can rest assured knowing that your calibration and verification requirements are being dealt with by the metrology experts.
Find out more and take a closer look at the maintenance contract solutions we provide here.