Measurement Tutorial 7
Keysight 34420A User’s Guide 289
RTDs
An RTD uses a metal (typically platinum) that changes resistance with a change in
temperature. Your meter can measure this resistance and by knowing the
characteristics of the RTD, calculate the temperature.
RTDs have the highest stability of the temperature transducers. Their output is
also very linear. This makes the RTD the transducer of choice for high accuracy,
long-term measurements. RTDs come in two main types: a = 0.00385 (DIN/IEC
751) and a = 0.00391.
The RTD resistance at 0 °C is referred to as nominal or R
0
. The meter can use
RTD’s with R
0
values from 4.9 W to 2.1 kW.
The meter always makes a 4-wire measurement of RTDs to preserve their
accuracy.
Thermistors
Thermistors use materials that change resistance with changes in temperature.
Your meter can measure this resistance and by knowing the characteristics of the
thermistor, calculates the temperature.
Thermistors have a higher sensitivity than thermocouples or RTDs. This makes
thermistors the transducer to use when measuring very small changes in
temperature. Thermistors are, however, very non-linear, especially at high
temperatures and function best below 100 °C.
Because of their high resistance, thermistors can be measured using two wire
measurement techniques. The meter supports 5000 W thermistors.
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