Induction heating of metal

The strong RF field used can heat up conventional heating devices and interfere with their electronics; fiber optics are immune to RF fields.

Plastic extrusion and injection molding

Precise control of the melt temperature is essential for polymer formation. An infrared reading eliminates errors that are common for thermocouple-based devices immersed in the plastic flow.

Temperature monitoring of drill bits

For high-speed PC board drilling, wear can be determined by optically monitoring drill bit temperature.

Semiconductor doping, deposition, or sputtering

Because these processes are usually carried out in a vacuum or controlled gas atmosphere using induction heating, conventional temperature measurement devices cannot be used.

Any high-temperature application where a direct measurement of the part temperature is critical to success is a good candidate for non-contact temperature measurement.

Copyright Omega Engineering Inc. All rights reserved. Reproduced with the permission of Omega Engineering Inc., Stamford, Conn. 06907 USA. www.omega.com.

Demystifying resistance thermometry

Tips from Minco, Minneapolis

Understanding resistance thermometry helps engineers get accurate readings from the two kinds of devices that leverage this technology.

Resistance thermometers

These thermometers consist of a metallic element in which resistance increases with temperature. Benefits include accuracy and stability. Their designs range from helical-wound thermometers for laboratory use to industrial thermometers made to conform to surfaces being monitored.

Resistance thermometers are sometimes called RTDs (resistance temperature detectors), PRTs (platinum resistance thermometers), or SPRTs (standard platinum resistance thermometers). These thermometers operate on the principle that electrical resistance changes in pure metal elements, relative to temperature. The traditional sensing element consists of a small-diameter wire coil wound to a precise resistance. The most common material is platinum, although nickel, copper, and nickel-iron alloys are used in many applications.

A more recent alternative to the wire-wound RTD substitutes a thin film of platinum, which is deposited on a ceramic substrate and trimmed to the desired resistance. Thin film elements attain high resistances with less metal, thereby lowering cost.

Resistance thermometers offer the greatest benefits relative to other thermometer types in the following situations:

• Accuracy and stability are the foremost goals of the application

• Accuracy must extend over a wide temperature range

• Area, rather than point, sensing improves control

• A high degree of standardization is desirable