Unfortunately the steps in this process do not appear to be widelyknown. The correct data con-version procedure for a reference junction at an arbitrary temperature is notdifficult. Turnkey thermocouple systems include a method fortemperature compensation for the reference junction. Since thermocouples can only indicate tem-perature differences, a reference junction is required to make an absolute tem-perature measurement. Thermocouple measurement devices range from hand-held units to multi-channel data acquisition systems. This document provides the necessary background andcomputational procedures for conversion of voltage measurements from thermo-couples fabricated in the lab, or purchased from a vendor. The proper fabrication and installation of thermocouplesis not discussed here. Thermocouples are inexpensive and versatile devices for measuring temperature.Thermocouples can be purchased in many different prefabricated configurations.For basic laboratory work, thermocouples can be easily fabricated from bulkthermocouple wire. A few of the more practical thermocouple circuits are ana-lyzed, temperature measurement with a basic ice-point reference circuitis described, and computational formulas for data reduction are given.Use of a zone box with a floating reference junction temperature is alsoexplained. Beginning with a description of theSeebeck effect, the basic equations relating EMF and temperature arepresented. This article provides a practical introduction to the conversion of ther-mocouple voltage to temperature. Permission is hereby granted for distribution of this document for non-commercial educational purposes so long as this document is retained intact, and proper attribution is given. In particular, the reader will see that one reason * Mechanical and Materials Engineering Department, Portland State University, Portland, Oregon, † This material is Copyright c 2001–2010, Gerald W. Readers wishing to use turnkey systems will benefit from understanding the process of data conversion. The goal of this document is to equip the reader with the knowledge and cal- culation procedures for converting raw thermocouple voltage readings to temper- ature. Unfortunately the steps in this process do not appear to be widely known. The correct data con- version procedure for a reference junction at an arbitrary temperature is not difficult. Turnkey thermocouple systems include a method for temperature compensation for the reference junction. Since thermocouples can only indicate tem- perature differences, a reference junction is required to make an absolute tem- perature measurement. Thermocouple measurement devices range from hand-held units to multi- channel data acquisition systems. This document provides the necessary background and computational procedures for conversion of voltage measurements from thermo- couples fabricated in the lab, or purchased from a vendor. The proper fabrication and installation of thermocouples is not discussed here. For basic laboratory work, thermocouples can be easily fabricated from bulk thermocouple wire. Thermocouples can be purchased in many different prefabricated configurations. 1 Overview Thermocouples are inexpensive and versatile devices for measuring temperature. Use of a zone box with a floating reference junction temperature is also explained. A few of the more practical thermocouple circuits are ana- lyzed, temperature measurement with a basic ice-point reference circuit is described, and computational formulas for data reduction are given. Beginning with a description of the Seebeck effect, the basic equations relating EMF and temperature are presented. Conversion of Thermocouple Voltage to Temperature Gerald Recktenwald *† JAbstract This article provides a practical introduction to the conversion of ther- mocouple voltage to temperature.
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