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Understanding Contact Temperatue Sensors

Semiconductor–based devices, thermistors, and ICs are well suited for use as component parts of electronic apparatus. The practice of packaging them in metal housings with threaded fittings would never have become established if today’s platinum devices had existed 20 years ago. RTDs and thermocouples are packaged with threaded fittings and connection heads and thermowells in order to facilitate their replacement upon failure.

Thermocouples are exposed to the harshest environments and highest temperatures and are therefore prone to failure at rates sufficiently high as to continue to justify the common industrial configurations.

When transistors first appeared, our vacuum tube mentality told us to expect failures and mount them in sockets. The failures proved to be mostly failures of the sockets and equipment reliability soared as the sockets were eliminated.

RTDs have advanced so far in the past decade that the practice of packaging them like thermocouples will gradually disappear. Most failures associated with current RTD installations are failures in the interconnecting hardware. As manufacturers learn to trust the modern RTD they will learn to mount them permanently in locations that will facilitate optimum operating efficiency at the expense of easy maintenance.

Considering that available, low-cost ICs can accurately digitize, in engineering units, the resistance of platinum RTDs with more than sufficient resolution to achieve all the accuracy available, it no longer makes any sense to sacrifice the universal interchangeability and stability of the RTD for the increased sensitivity of the semiconductor-based devices. Manufacturers who are slow to recognize the significance of this will find themselves at a serious competitive disadvantage. Their equipment will not only cost more, but it will also be less reliable.

While there will always be certain applications that require the fastest or most sensitive component regardless of cost, it is clear that in the temperature range from -200°C to 600°C the use of any contact temperature sensor other than a platinum RTD will be increasingly difficult to justify.


Irwin Bluestein is National Sales Manager, RdF Corp., 23 Elm Ave., Hudson, NH 030510490; 603-882-5195 or 800-445-8367, fax 603-882-6925, www.rdf corp.com

©RdF, 2003, Edited.
Original Publishing:
SENSORS, January 1999


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