Temperature Measurement Devices for HVAC-R

Temperature Measurement Overview

Heat is a form of energy that flows between two samples of matter due to their difference in temperature. Temperature is a measurement of heat energy and is defined as the warmth or coldness of a substance with reference to some standard value. There have been many methods developed and used to measure temperature from simple thermometers to sophisticated, highly accurate, electronic transmitters.

Siemens SITRANS T products provide highly accurate, temperature measurement transmitters and sensors for any commercial and industrial application.

Types of Temperature Measurement

Electronic temperature transmitters used for commercial and industrial temperature applications typically employ the use of either thermocouple or resistance temperature sensors. Both types have both pro’s and con’s associated with them, and selection is dependent on the application specifics.

Thermocouples – A temperature sensing element consisting of two joined dissimilar metals which when heated produce a small voltage proportional to temperature. When the junction of the two metals is heated or cooled the voltage produced varies and can be correlated back to the temperature.

Advantages

  • Low cost

  • High temperature applications

  • Quick response

Limitations

  • Accuracy

  • Oxidation issues

Resistance (RTD) – A temperature sensing element consisting of a wire with a known resistance which when the measured temperature changes so too does the resistance in the wire. A small current sent through the element will vary depending on the resistance/temperature effect and can be correlated back to the temperature.

Advantages

  • High Accuracy

  • Long term stability

  • Robust

Limitations

  • Wide but limited measurement range

  • Higher cost


06/14/2012 | Author: Ryan.Shea@siemens.com

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