Understand Calibration Source Criteria (Pt 3)
There's more to calibration than reading digital displays.
Editor’s Note: This is part three of a three-part series.
The first column in this series dealt with preparing a list of equipment you want an outside source to calibrate for you. The second looked at using scopes from different labs to compare them and their suitability for what you need in the way of calibration. This one looks at other factors that may be used in arriving at a final decision.
Some folks select the calibration source based on convenience. They reason that the best choice for them is the lab down the street or around the corner because they don’t have to ship their stuff any distance to get it done. This may save on packaging and freight but should be the very last thing to consider if your short list has two or more facilities on a technical par.he first column in this series dealt with preparing a list of equipment you want an outside source to calibrate for you. The second looked at using scopes from different labs to compare them and their suitability for what you need in the way of calibration. This one looks at other factors that may be used in arriving at a final decision.
Another condition frequently imposed on the process is the desire to be able to send all your different types of equipment to a single calibration source. Using this approach, gage blocks and other dimensional equipment would be sent along with electronic instruments etc. to that source.
Technically speaking, if the items you are sending are on their accredited scope, you should be able to do this. However, you may discover the hard way that the lab’s area of expertise is electronic instrumentation for example, rather than the dimensional metrology involved. This will cause problems when you have questions of a technical nature and they can’t provide answers. This situation arises frequently when fixed limit gages, particularly thread gages, are involved. There’s more to calibration than reading digital displays.
Some companies believe that if they return their equipment to the maker of it, they’ll get the best results and this usually occurs but not always. There are a number of reasons for this, which is a subject for another day, but my experience and that of many companies in this field is that using this approach is not as reliable as you might expect. Where instruments are involved, you may find that the company you thought was the maker of them is really an importer or distributor of the device you are concerned about with little or no calibration capability at all.
Many manufacturers of gages and instruments opt to become accredited for their calibration work to provide that extra assurance for people who buy their products. Some offer a choice between accredited and non-accredited reports, the latter being more expensive while the former may even be ‘free.’ The difference is that the accredited report will cover work done by someone other than the person who made the gage, for example, the environment and equipment will be more strictly enforced and the person doing the work will be free of production pressures. Okay, I can hear you asking: Isn’t that the way this stuff should be made anyway? It used to be but the ongoing pressure on manufacturers for lower product prices means cuts have to be made somewhere when the usual options are used up.
One step you can take to ensure you get what you need after you’ve waded through this series is to visit the labs on your short list. I’m not talking about an audit, just a friendly look at the facility and equipment they have—to make sure they have what you think they should have. This is a good opportunity to discuss what you’ll get in the way of reports because accreditation does not provide any guarantees on the level of detail to be provided in most cases.
I became involved in a dispute where the purchasing department made the decision on who got the calibration order based on price but the report that was received wasn’t worth having. The supplier only took one reading for size on a gage member and reported it as though several readings were taken when they were not. More infuriating was the revelation that the lab in question was using a rinky-dink piece of hardware for the work that was barely good enough to measure machined parts.
Calibration is no different than any other service you may use professionally or personally. There are those who are very good at what they do because they know what they’re doing, those who don’t know what they’re doing and are not so good. And there are those who know they don’t know but do it anyway.