Book Analog Interfacing to Embedded Microprocessors
RTD
An RTD (Resistance Temperature Detector) is just a wire that changes resis-
tance with temperature. Typical RTD materials include copper, platinum,
nickel, and nickel/iron alloy. An RTD element can be a wire or a film, plated
or sprayed onto a substrate such as ceramic.
RTD resistance is specified at 0°C. A typical platinum RTD with 100 W resis-
tance at 0°C would have a resistance of 100.39 W at 1°C and a resistance of
119.4 W at 50°C. The tolerance of RTDs is better than thermistors. Typical tol-
erance for RTDs looks like this:
Platinum: .01% to .03%
Copper: .2%
Nickel and nickel/iron: .5%
Aside from better tolerance and overall lower resistance, the interface to an
RTD is similar to that for a thermistor.
Thermocouples
A thermocouple is made by joining two dissimilar metals. Thomas Seebeck
discovered in 1821 that when such a junction is heated, it generates a tiny
voltage
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