* * * INSIGHT * * *

What you should know but don’t

or

How does a thermocouple work?

by

Thomas A. Jennings, Ph.D.

Often during a discussion on lyophilization I will playfully ask what appears on the surface to be a simple question. I must admit I find the puzzled expressions on the faces of those present  to be most interesting. Sometimes they appear as if they have just been struck by lightening. But it is not lightening that has affected them it is the realization that something so simple is some how difficult to explain.

The questions are often very basic in nature and on a topic that most people take for granted. For example, during the lyophilization process one can only control two intensive variables, i.e., pressure and temperature. Pressure measurements have already been considered in a previous INSIGHT (Vol. 1 No. 6) so I though I might just direct my attention to the temperature measurements.

Temperature measurements in the field of lyophilization are often made used using either a RTD (resistance thermal device) or a thermocouple. Most people who I encounter have no problem explaining how an RTD functions. A change in resistance is associated with a change in temperature. In most devices, an increase in resistance is an indication of an increase in temperature. But there is often a look of shock when I ask how a thermocouple works. They are well aware of the fact that two dissimilar metals are involved but just how they are used to determine a temperature now becomes a bit of a mystery. With this in mind I thought that I would make the workings of a thermocouple the subject of this INSIGHT. But why the strange title? Well I shall let our good friends at the Surcure Company, Armondo and the Novice, tell you how the title came about. In addition, I thought another visit  to this company  might add a smile or two to the face as we approach the end of the vacation or holiday season.

.Volume 4  No. 8                                                                                August 2001

6 Pages          No  References          2 Figures

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