Characteristic |
Thermocouple (T/C) |
Resistance Temperature Detector (RTD) |
Measurement Range |
Wide, -250°C to +2600°C |
Narrower, -200°C to +850°C, often limited to a
lower temperature by its insulation. |
Output Signal |
Voltage wrt difference in end-to-end
temperature |
Resistance change wrt actual temperature |
Accuracy |
Less accurate, 2-4°C typical |
More accurate, up to 1°C typical |
Long Term Stability |
Fair, limited to shorter periods |
Good, stable over long periods |
Stability/Drift |
Good, but more subject to drift |
Excellent, better long-term stability |
Sensitivity |
Lower |
Higher sensitivity |
Interchangeability |
Good |
Excellent |
Linearity |
Fair linearity, special linearization
generally required. |
Better linearity, special linearization still
required, but to a lesser degree |
Self-Heating Error |
No self-heating error |
Some self-heating error, but low |
Extension Cable |
High effect, must match T/C type
and is more expensive |
Lower effect, can use different material, but
ultimately limited by lead wire resistance |
Response Time |
Fast (≤ 0.1 seconds typical), but
CJC has thermal lag |
Slower (1 to 7 seconds typical) |
Repeatability |
Reasonable |
Better & greater standardization |
Hysteresis |
Excellent |
Good |
Signal Strength |
Low, prone to EMI |
Higher, more EMI resistant |
Vibration/Shock Resistance |
Good resistance |
Less resistant than T/C |
Robustness/Ruggedness |
Very good |
Good |
Sensor Dimensions |
Very small to very large |
Small to medium |
Measurement Area |
Small, single point-of-contact |
Larger, whole element must contact, 1” typical |
Fine Wire Diameter |
Small down to 0.25mm diameter |
Larger up to 3mm diameter |
Reference Junction |
Required and a significant source of
measurement error. Usually requires
a stable ambient at cold junction. |
Not required and not a source of error |
Excitation Required |
Not required, self-powered |
Yes, reference voltage or current source |
Lead-Wire Resistance |
High, but often mitigated by mating
technology |
Must be considered wrt maximum added
resistance and potential resistive imbalance
between leads |
Cost |
Less expensive |
More expensive |
Complexity |
Very simple and less subject to
mechanical stress |
Physically larger and has a more complex
construction making it more subject to
mechanical stress |
Calibration Ease |
More difficult and adds CJC
calibration |
Less difficult, no CJC to contend with |
Noise Immunity |
Lower noise immunity but often
mitigated by good wiring practice.
Small signals and high impedance
leads can easily pick up noise. |
Better noise immunity than a T/C |