In a recent post, I said that one of the important features in a calibrator is flexibility or versatility. You might say it’s the Swiss Army knife (a registered trademark of Wenger S.A. and Victorinox A.G.) effect. I know that sometimes mashing things together makes a whole that’s a lot less than the sum of its parts, but…

For calibrators that’s not the case. In fact, because they are often the most highly engineered products a company offers, multi-function calibrators may offer the best overall performance in a company’s line. There don’t really need to be too many tradeoffs.

Sure, the multi-function calibrator is likely to be larger than its single function relatives and certainly a bit more complex, but having every tool you need everytime you need it is worth it for many. Our MC-1200 has the capabiltiy of a loop calibrator (and just as easy to use), a high performance temperature calibrator (just about every T/C and RTD curve you can think of), a wide ranging pressure calibrator (29 ranges and styles of Beta pressure modules), DC voltage and frequency (with pulse train output).

That’s what I mean about versatile.

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.

Sometimes we just have to pat ourselves on the back. Well, not really, our customers often do it for us. Here’s a recent example that was completely unsolicited. 

We have managed to procure your equipment through our broker in South Africa and I am satisfied with the performance especially the Multi function calibrator DMC-1400 and the pressure calibrator model BetaGauge 311.

 

Thanks for the quality products. – Ephraim

It’s great when someone says thank you, and it’s great to know that our products are helping get things done all over the world. You can find out more on this web site or by seeking out your local Martel Electronics Distributor.

Temperature sensor calibration is not something industrial technicians often deal with. At most, they’re going to tweak a transmitter or some receiver device to reduce or eliminate the inherent error in the sensor. Unfortunately, that can only be done at a single temperature.

Martel 3001

It’s a different story for higher end devices like the Martel 3001 Bench Calibrator or even our hand held MC-1200 and DMC-1400 multifunction calibrators. For them you can enter constants for your temperature sensor so it is matched to the calibrator across the entire measurement range. This makes the calibrator into a very accurate thermometer.

This begs 2 questions. One, how do I get those contants to enter into the calibrator, and, two, what’s the point of doing this?

First, let’s make one point clear. The probes we’re talking about are resistance temperature detectors (RTDs), sometimes also called PRTs or SPRTs. The Hart Scientific guys over at Fluke have a very nice white paper about how to take a probe more or less off the shelf and get the constants for it. However, you normally get the constants from the probe vendor. These kind of probes cost more as you have to pay for the data.

The 3001 can use either Calendar-Van Dusen constants or ITS-90 data for curve fitting. The hand held calibrators only work with the Calendar-Van Dusen constants.

Other than for checking the temperature of something what’s the point of this? Well, that is the point and the most useful and common application is to use the calibrator/probe combination with a dry well temperature calibrator to improve its overall performance in testing and calibrating temperature loops.

A couple of weeks ago, Jim Cahill of Emerson Process commented in his blog about the importance of getting back to basics in instrumentation and controls. His point was that no matter how sophisticated, expensive or new your system is, it can still be an automation or control disaster.

He talked a lot about an installation that suffered from poor loop tuning and the like, but this also applies to instrument calibration.

It seems obvious, but poor or inaccurate calibration will cost you a lot more in money, materials, headaches and safety than what the fix costs.

Here are a few things that are what I think about when I say back to basics in calibration.

• Use modern equipment. Newer calibrators make the job easier and easier to do with great accuracy. The accuracy of calibration equipment today is much better today than 20 years ago.
• Keep your calibrators calibrated. Some people are surprised to learn that even calibrators need to be calibrated. Whether you use the original manufacturer for periodic recalibration or a third party lab or maybe even an in-house lab, calibrations need to be kept up-to-date. That means a qualified NIST or other national lab traceable calibration with data.
• Use automated calibrations and automated documentation. Not only do these features make the job easier and provide good calibration history, they also prevent errors in the work.
• Do the routine work. If you’re always putting out fires, you’ll always be putting out fires. Routine, regular calibration does pay off. I know, this is really a management problem. You just have to keep asking for the resources long enough to be a real pain in the you-know-what to actually get the resources. This is where using modern equipment helps, too, because it can stretch out the staff you have to get more work done.

Wanted Dead or Alive

WANTED DEAD OR ALIVE!

OLD BETA, PROMAC OR MARTEL CALIBRATORS

If you have an old BETA, Promac or Martel calibrator, it’s worth money even if it doesn’t work!

When you buy a new DMC-1400 Documenting Multifunction Calibrator, MC-1200 Multifunction Calibrator, BetaGauge 311 or 321 or the new BetaGauge 330, your old calibrator is worth $300 towards the purchase.

You can request more details on our web site or just call Tracy at 800-821-0023, extension 103. She’ll be glad to help. You can also send an email to sales@martelcorp.com to request more information.

When someone mentions calibrator uncertainty, they are talking about what we call accuracy in our specifications. To be strict about it, our accuracy specifications are inclusive of most or all errors. In scientific applications, you might see these all broken out.

Typical examples are errors from linearity, hysteresis, ambient effects and others. In most cases all of these errors are combined into a comprehensive specification. That makes it easier for a user to determine the applicability of the calibrator for a given purpose. This number would then be the total uncertainty of the calibrator for a given calibration.

However, if the calibrator is to be used to make a measurement, you might also have to consider the uncertainty of the primary element or sensor. Let’s take the example of the Martel BETA PTC-8001 being used as a thermocouple thermometer to measure a process temperature. Here, you need to also consider the uncertainty of the thermocouple and thermocouple extension wire to make a determination of the total uncertainty.

In calibrating a transmitter, the sensor is not used, so there is no need to consider sensor error in that case. For resistance sensors (RTDs), you would have to consider an error (lead wire resistance) if you are using only a 2 wire connection. For 3 and 4 wire connections, the lead wire error is too small to be of consideration since we have a compensating measurement.

For calibrating a thermocouple instrument, you must use the correct type of thermocouple extension wire for the cold junction compensation to work correctly. There is a very small error even with the thermocouple extension wire, but it is too small to be of any practical concern. The length of the thermocouple extension wire should be kept short. We typically recommend no more than 1 meter.

We’ll have more on uncertainty in transmitter calibrations in the next post.