We (people actually in the calibration industry) often hear things being called calibrators that obviously aren’t. A great example is the Emerson HART(tm) communicator. No offense intended, but these types of devices aren’t calibrators, they are electronic “screwdrivers” that enable a technician or engineer to adjust the calibration of a device.

Here are my defining points for a calibrator.

1. Can make a precision measurement or generate a precision signal (i.e., analog, not digital). Or BOTH.
2. Has a calibration that is traceable to national standards.
3. Has a known accuracy or degree of calibration uncertainty.

There is a lot that could be added to this list, of course; things such as conformance to international standards, EX ratings…

Another little list of mine is this list of characteristics that make up a good calibrator.

• Accuracy
• Flexibility or versatility
• Ease of use
• Reliability
• Ergonomics (small, lightweight, easy to read display, etc.)
• Value

To me, a great example of all of the above is the Martel BETA MC-1200 Multi-function Calibrator. It’s got a long list of features, top knotch performance and is a great deal for the money. Total cost of ownership is good because all they ever require is annual recalibration which anyone with a computer and adequate standards can do.

Martel calibrator user Bruce Schmeck is quoted in the March, 2010, issue of Control Magazine saying, “We use field calibrators…for all kinds of biochemical batches to monitor and verify temperature, pressure, flow and agitation.”

In the same article, one of our competitors surveyed users and unsurprisingly discovered that a lot of them aren’t calibrating the instruments in their plants.

The article goes on to point out that many users have been sold a bill of goods about their instrumentation from the makers of that instrumentation. To wit,”our digital instruments don’t drift, so they don’t need to be calibrated.”

BetaGauge 321A Dual Range Pressure Calibrator

Mr. Schmeck also explained in this article that it isn’t the digital part of new instruments that drifts; it’s the part where the rubber meets the road, so to speak. He cites the example of the metal diaphragm in a pressure transmitter. The metal will age and its response characteristics will change over time. The ONLY way to fix that is to use a traceable field calibrator to inject a known valid signal.

To sum it up, here’s another quote from Bruce Schmeck that I like, “Most calibrators need to be re-calibrated once per year.” I love it.

I’m not referring to an old time game show or parlor game as they used to be known. My question is, “Can you trust your vendor’s calibration certificate?”

There are a few indicators you can use.

1. What kind of reputation does the company have in the industry? You know, how long have they been around and do other customers respect their products and service? There are a number of industry surveys and reports that can help with this if you don’t feel comfortable making your own assessment.
2. Is the certificate traceable to NIST or other national standards body? This may seem obvious, but read the statement see if it makes sense to you. Are there unsupported assertions about things like TUR (Total Uncertainty Ratio) or Guide 25 approval?
3. Are the standards used properly identified and are they appropriate for the task at hand? For example, if a specification is % of reading, but the standard’s specification is % of scale, there’s a significant mismatch. You may also need to check to see if the standard has been properly maintained with acceptable calibration intevals.
4. Does the certificate include data that is clearly presented and meaningful? Are there sufficient data points to assess performance?
5. If possible, check the calibration at intervals different from the cardinal points on the certificate. Even a bump check can provide revealing information.

Finally, is the calibration accredited under an international standard (ISO 17025) or do you need such an accredited calibration. Even if it’s offered as an option, the vendor must have a pretty good idea that the normal calibration is valid.

There is an interesting discussion thread going on at Linked In about whether plant operators should be allowed to adjust or change instrument settings (including calibration).

If you are on Linked In, you can find the discussion here http://bit.ly/1ez5lo. If not, you’ll need to sign up for a free account.

My personal and professional opinion for calibration is a decided NO. Actually, it’s NO, NO, NO, NO!

Inadequate calibration maintenance is already a plague at most process plants and allowing anyone other than a qualified calibration professional with the right tools to make a change that affects calibration is sheer madness and dangerous to boot.

While a little tweak may appear to fix things momentarily, pretty soon it will add up to a huge problem.

I feel qualified to make this statement having worked on both sides of the equation. Operators do need to feel and be empowered, but that should be limited to making setpoint adjustments, which even then may need to be limited. It’s easy to lose the big picture when you’re having a problem in the control room. Setpoints, calibration, etc. all have to come together to make the big picture pretty.

Sometimes it’s helpful to give definition to some basic terminology used in the calibration game.

Here are a few to get started.

Calibration – the application of a known value (electrical, mechanical, etc.) to a device and the determining that its output accurately represents the applied value. Note: sometimes this definition is modified to include any adjustments necessary to bring a device’s performance into specification.

The definition of a calibrator is corollary, a device of known accuracy that simulates and/or measures a known value (electrical, mechanical, etc.).

Traceability – the prinicple and documentation that allows the tracing of the calibration of a device back to a primary standard maintained by a national standards organization such as the N.I.S.T.

N.I.S.T. is the National Institute of Standards and Technologies (bureau of the U.S. government). This was formerly known as the National Bureau of Standards. It coordinates with other national bodies around the world so that a kilogram is a kilogram worldwide.

Now, here’s a little more detail on some confusing side issues:

Configuration vs. Calibration vs. Verification vs. Confirmation. Due to the lack of a standardized terminology, calibration is often confused with other terms and activities including configuration, verification and confirmation.

Configuration generally means the adjustment of the measurement and / or transmission capabilities of a device to alter its function or use. For example, the measurement range of a thermocouple transmitter may be changed from 0 to 100 degrees Celsius to 0 to 200 degrees Celsius. This would not represent calibration unless a calibration device as defined above was used in the process to determine the accuracy with which it represents this change in its output. The term often applies to the use of a configurator or “electronic screwdriver” to alter the operation of a “smart” transmitter.

Calibration properly refers to the use of an external independent traceable standard to verify that the input to output relationship of the instrument is in specification and to make whatever adjustments may be required to establish that relationship within specification. Note that there is the use of the word verify in this definition.

Confirmation and Verification can be used interchangeably. Again, they refer to the use of an independent standard, but generally do not imply the adjustment part of the calibration definition. The use of these terms is fairly recent.