Analog Terminal Board
Reference
fitted.
Thermocouple Outputs.
A thermocouple is the junction between two dissimilar metals,
the TYPE of thermocouple depends on the metals used.
Thermocouples generate an output voltage that varies with
temperature, as observed initially by T. Seebeck in 1821. Thus
by accurately measuring the voltage generated by a thermocouple
the temperature is precisely known.
Unfortunately the relationship bewteen temperature and voltage is
not a linear one. IE the graph of temperature against voltage is
not a straight line. The situation is further complicated by the
fact that different types of thermocouples are needed to cover
different temperature ranges and each thermocouple types voltage
output has its own particular way of varying with temperature.
The best way of turning a thermocouple voltage into
temperature, and vice versa, is by using a printed table. Several
are in use. Two common sources of data are the American
National Standard C96.2 1973, published as ASTM document E
230-72 and "Temperature Sensing with Thermocouples and
Resistance Thermometers" by Labfacility Ltd available from
Farnell as order code 182-714 price £2.90. The different types of
thermocouple are known by various letters of the alphabet eg J,
K, R, S, T, B, and E etc. Figure 1-x is taken from ASTM
document E 230-72.
Page 7
