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What is Calibration?

So, for one reason or another, you've been tasked with investigating a calibration program for your firm? Perhaps the decision has been made to become ISO certified. Maybe customer requirements are becoming stricter. It may even be as simple as you investigating if your current calibration solution is optimal.

In any event, congratulations! You are taking a major step forward in improving the quality of your company's end product, whatever that may be.

Before one can begin to explore the seemingly overwhelming challenge of implementing or overhauling a calibration program, it is important to first understand what calibration actually is. There are a lot of misconceptions out there.

Definition

There are many formal definitions that exist. One of the more common ones is:

Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties (of the calibrated instrument or secondary standard) and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.

             - International Bureau of Weights and Measures

Wow. That was a pain just to type.

As someone who has been around the calibration industry my whole life, I have often gotten a lot of blank stares when trying to explain the technical aspect of calibration (let alone the times that having the word "metrology" in our company name led to us being asked to forecast tomorrow's weather). It led to me having to formulate my own definition:

Measuring things that measure things.

             -  Steve Toll

Now, quoting this definition is not going to help you pass any Masters degree thesis, but it does the trick. As simplistic as this statement is, it accurately captures the essence of calibration. Any calibration, no matter how complicated, boils down to comparing a known reference to a device that is intended to precisely measure another item. It is a system of comparison.

System of Comparison

So how does this comparison process work? Perhaps the easiest way to visualize this concept is through a situation that I have admittedly grappled with myself:  the bathroom scale.

If you are like me, every year around late December, you decide to take a serious look at your fitness. You then spend some time thinking about your diet and activity levels and realize that the words "beer", "brats" and "football" appear far too often. But not this year. This is the year you develop a strict regimen and become the sports star you always knew you could be. 

So January 1 rolls around and you hit the gym hard. Your diet switches over to things mostly consumed by rabbits. You stick to this plan for a week solid. You even go out and buy yourself a new, fancy scale that connects to your phone.

At the end of the first week is the big moment. You climb on that new scale expecting a moment you'd see in the "The Biggest Loser".  However, you look at that scale and the number you see shocks you in disbelief. You weigh the same as you did to start!

Now, this post is not intended to go down a personal fitness training path, but how could this be? You have put everything you could into this past week and nothing has changed. Inevitably, you may come to the same answer as many people have, the scale "isn't measuring properly" (please note the heavy sarcasm).

How can we be sure this is the case? Calibration. The process of checking this scale would be as simple as taking a known weight, placing it on the scale and comparing the known value to the reading on the display.

Traceability

Back to the example. Let's say after completing this test you find your scale to be reading perfectly accurate. Well, the "only logical" solution is that the weight used to check the scale must not actually be the weigh what it states it does, because "of course you lost weight" (heavy sarcasm again).  How do we assure this is not the case?

The answer is through traceability.

Although this concept is enough to take up several posts of information, the concept is fairly easy to describe. Traceability is the link from the measurement result back to the theoretical concept of the unit you are trying to measure - in this example, a pound. This means that by using a traceable calibration process, you can guarantee that the reference you are using is a fair representation of this measurement unit. 

Adjustment

Now, let's flip our example around. Let's say you got lucky and you find that the scale was reading 5 pounds too heavy. Phew. All of that hard work was not in vain. After your moment of rejoice, you now realize that you have two options:

  1. Live with it and always subtract 5 pounds from your reading.
  2. Adjust the scale to read accurately.

I think most of us would prefer the second option. Who wants to do math after a hard workout, anyways? So, how does the calibration procedure address this? It doesn't. If you refer back to the formal and much less informal definition of calibration provided earlier, adjustment is not mentioned anywhere. This is because calibration and adjustment are two separate things and should always be viewed as such. 

If you choose Option 2 above, you, of course, will want to recheck (re-calibrate) the scale after the adjustment. After all, you will want to make sure that you adjusted it all the way back to where it should be reading. Using the formal definitions, this sequence looks like this:

  1. Calibration
  2. Adjustment
  3. Calibration

This process would need to be completed until the scale is adjusted correctly.

Hopefully, this is a fairly easy differentiation to make. However, in the quality industry, the lines are often blurred. Many people tend to see this as an all-in-one process. Although an adjusted gage has the same outcome as a gage that passed calibration the first time, it is important to remember the distinction between the two.

About the author

Steve Toll

Steve has been around the calibration industry his whole life. His father, Mark Toll, founded Fox Valley Metrology in 1996, when Steve was only 6 years old. Steven went on to graduate from Milwaukee School of Engineering, one of the most challenging and accolated technical universities in the country. This lifelong immersion in the industry has led him to become the Vice President of Sales for Fox Valley Metrology since 2014.

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