MeasurementBlog

Do you understand Thermocouples?
http://www.youtube.com/user/ControlEngineeringTV
Control Engineering Editor Peter Welander demonstrates the concept and use of thermocouples, including one made from scrapbox components. (10 minutes). I think this is a lot cooler than the TV ads for Sprint mobile that Dan Hesse makes (in MHO). Way to go, Peter!

This eighth essay in a series on Sensorsmag.com. It is reproduced here with permission of SensorsMag a Questex Media Group, Inc. publication. The format has been slightly changed to make it easier to read online.

Jul 22, 2008 – by: G. Raymond Peacock, Temperatures.com Inc. – Sensors

This is the eighth essay in a series expanding on an article I wrote for Sensors titled “A Twelve-Step Sensor Selection Checklist.” In May, I talked about the process of soliciting bids. This month, I’ll focus on acquiring a sensor, or measurement device, and expert technical services.

A Source of Expertise
Keep in mind, the sensor supplier is an expert in the sensing area in which you are involved and a valuable technical resource, regardless of your own level of experience.
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This is the fourth essay in a series expanding on an article I wrote for Sensors titled “A Twelve-Step Sensor Selection Checklist”.

(Note: It has been modified very slightly to make it more easily read in this format)

In October (2007), I discussed the need to consider factors that influence measurement conditions. This month, I’ll talk about other considerations and best practices for making a list of sensor candidates.

Don’t Forget the Big Picture
Before you can get a clear idea of the sensor you need for your application, you must see the broad perspective. Remember, the sensor is part of a larger, multifaceted system. So, you’ll have to keep a number of things in mind.

For example, make sure the sensors you select for your list include installation and interfacing components that meet the needs of the application.

A few years back, I was involved in a project in which we had to run signal and power cables 30 meters, from a shielded instrumentation room to the measuring device. The cable was installed in an extremely hostile environment, where the ambient temperature ranged from nearly 0°C to over 100°C.
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About 25 years ago, I first visited the Instrumentation Labs at Oak Ridge National Laboratories (ONRL) at the invitation of the late Bob Shepard. Bob was a pioneer in many areas of temperature measurement and at that time was the Chairman of ASTM Committee E20 on Temperature. He was also head of the lab at ORNL.

He introduced me to Johnson Noise Temperature (JNT) measurement and showed me a prototype device that they had developed at Oak Ridge to implement the method as an possible alternate means to verify the calibration in situ of thermocouples in a nuclear reactor environment.

While the method was very complex, Bob was convinced it would eventually become commercially viable, if for no other reason than it was a fundamental technology related to the Absolute Thermodynamic Temperature Scale (Kelvin Scale) and required no calibration.

Work has continued to this day at ORNL and elsewhere. More recently, the staff at the National Institute of Standards & Technology (NIST) Thermometry Group have been producing some remarkable results, prototype devices and a raft of technical papers on the subject.

First a description about this unique temperature measurement method that has been studied for more than 30 years.
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