by Richard A. Litts, Founder and President, Litts Quality Technologies, Inc.
We all have the pleasant experience of pulling into a gas station and deciding which grade to purchase for our vehicle. Sometimes our decision is based upon the manufacturer recommendation while other times it is a matter of price. Usually there is a sign outside the gas station showing the price per gallon in an attempt to entice us into believing one is better than the other. When you look at the sign and it shows: $1.559, $2.659 or $2.799, how do you know that you are getting what you pay for? The same holds true when you visit your local supermarket and purchase cold cuts in the deli. How confident are you that you actually get one pound of that Honey Oven Roasted Turkey Breast for $8.99? The answer hopefully is that the gas pump metering device and the deli weighing scale are calibrated. Next time you do one of these activities take a look – do you see a calibration sticker from a qualified source? Is it within the calibration frequency or has it expired?
Calibration is the process that determines if the monitoring or measuring equipment is being compared to a standard that is “traceable” to a known artifact. The Department of Defense defines traceability as – “The ability to relate individual measurement results to national standards or nationally accepted measurement systems through an unbroken chain of comparisons.”
In the United States we typically look to the National Institute of Standards and Technology (NIST) as the competent organization to provide manufacturing companies a traceable standard.
The Hierarchy of Standards may be defined by:
National – NIST or designated authority (laboratory)
Primary – Transferred by NIST
Secondary – Performed by organizations with access to Primary
Working – Used to calibrate measuring equipment in a manufacturing facility
If NIST or another national governing body doesn’t have a standard for your monitoring or measuring equipment, you create your own and define the process for determining the standard. You want confidence that the product you are producing is meeting your internal and external customer requirements. Calibration is a significant part of providing assurance that you are meeting these requirements. We know that if we aren’t meeting internal customer requirements we probably won’t meet external customer requirements. Control of monitoring and measuring equipment is part of Quality Management.
These coordinated activities of doing things up front before the request reaches the “Producing Process” typically cost manufacturing facilities less money in the long run. Many of the ISO Management System Standards have a requirement that when you calibrate monitoring or measuring equipment it is out of “tolerance” you have to assess and record the impact of how much it was out of “tolerance” on all product that was monitored or measured since the last time it was calibrated. In practical terms, this means that if you calibrate a micrometer on a yearly basis, you have to go back and assess the impact on all product that was measured using that micrometer since the last time it was calibrated. That is one-year worth of data and you must have a record of the assessment. The worst case is that you have to notify your customer that you may have shipped them nonconforming product.
Some years ago a company that publishes case studies was interested in implementing a quality management system. During the development process, I asked them how they knew all of the required documentation is included in the report binder. The owner said, “we weigh it”. The next logical step was to take a look at the weighing scale. In our discussion I asked if the scale was calibrated. The reply was – “not sure”. I then asked how confident he was that the scale would pick up a single sheet of missing documentation from the binder. The response – 100%. I took a stack of paper, turned on the scale and started adding sheets. As I added sheets, the owners’ facial expressions began showing concern. After placing the eighth (8th) sheet the scale registered the first digit. In this case there were two issues. One was having the correct equipment that would detect one missing sheet and the other is having the weighing scale calibrated. It is the responsibility of top management to make sure that the monitoring and measuring system is capable and calibrated. This includes providing resources to 1) make sure the organization has the right monitoring and measuring equipment, 2) make sure that if calibration is performed in-house that employees have the skills and can apply those skills to perform calibrations, 3) to communicate to the organization the importance of using calibrated monitoring and measuring equipment, and 4) maybe most important…the impact of not using calibrated monitoring and measuring equipment. If not, the results can be very costly in terms of scrap, rework or missed customer commitments.
Mr. Litts will be the instructor for an upcoming workshop offered by NWIRC, “Calibration and Using Measuring Equipment”, on April 24 and 25, 2018. Click here for more details and to register.
Photo: Previous Calibration Workshop, with instructor Richard Litts, hosted by NWIRC.