Preproduction Testing

In preparation for a new product launch, Martel is adding new temperature calibration equipment. The 2 major pieces are a Fluke Hart Scientific 9210 Triple Point of Water and a Fluke Hart Scientific 7341 High Precision Temperature Baths.

Here are some pictures of the new equipment, which is shown being used in preproduction testing now. By the end of our summer they will become the foundation of a production temperature calibration lab.

Hart 9210 Triple Point of Water

Hart 7341 Precision Temperature Bath

We have updated the very popular and powerful BetaGauge 311 and BetaGauge 321 Advanced Pressure Calibrators. The new models are the single range BetaGauge 311A and dual range BetaGauge 321A. What we didn’t change are the great performance and ease of use we already had.

Here are the new features:

• Super rugged “Power-Tool-Tough” housing. We’re using the same plastic used in high end cordless drills and the like to make the BetaGauge 311A/321A virtually indestructible.
• Custom engineering units. If you don’t like any of the 19 built-in engineering units, you can configure up to 2 additional units. If you give us the factor information and unit name at the time of order, we’ll even put it in for you at no extra cost.
• Enhanced measurement stability. We updated the circuit design on the pressure sensors with our latest technology to provide better all around performance over a wide range of temperatures and with less long term drift.
• User selectable resolution. Sometimes, there’s too much resolution for the intended application. Those extra digits can make the job harder not better. So, you can reduce the displayed resolution by a single digit in any application.
• More compatible ranges. With 29 possible ranges, we let the user choose what’s right for them. Now, we’ve made the ranges more compatible with long time industry practice by providing compound measurement on most ranges below 500 PSI (35 Bar).

See our web site for more details. The new calibrators are available NOW!

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.

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.

In the current issue of Scientific American magazine, there is a short blurb about the invention of a new kind of thermometer that is able to interpret data directly tied to a fundamental number, the Boltzman constant. See the article here.

Physicists like that kind of stuff. You know, a meter is the distance light of a certain wavelength travels in a vacuum in a very short period of time. I have to admit, I’m not sure how they measure 1/299,792,458th of a second.

Anyway, I’m glad that we in the industrial and process calibrator business don’t have to get down to that level. All of our common signals end up being mostly DC voltages. They are pretty small and you have to design to keep noise and interference from ruining your measurement, but it can be done with great accuracy.

Martel’s real claim to fame in the temperature calibration game, is simulation of RTD signals along with very accurate measurement of the same.

PTC-8001

A big challenge for RTD simulation is the ability to simulate to devices that strobe or pulse the excitation current. You have to be able to measure the current quickly and accurately, and then generate an opposing voltage that looks like a resistance to the device on the other end.

We have also learned to be able to measure RTD signals with lab accuracy in a hand held device. Have a look at our PTC-8001 temperature calibrator for a great RTD calibrator that also has a great thermocouple calibrator hidden inside.