Thermocouples ANSI
Comparison of Sensor Types
|
Thermocouple |
Platinum Resistance Thermometer |
Thermistor |
Sensor |
Thermoelement, two dissimilar metals/alloys
|
Platinum-wire wound or flat-film resistor |
Ceramic (metal oxides) |
Accuracy (typical values) |
0.5 to 5.0°C |
0.1 to 1.0°C |
0.1 to 1.5°C |
Long term Stability |
Variable, Prone to ageing |
Excellent |
Good |
Temperature range |
-200 to1750°C |
-200 to 650°C |
-100 to 300°C |
Thermal response |
Sheathed – slow Exposed tip – fast 0.1 to 10 secs typical |
Wirewound – slow Film – faster 1-50 secs typical |
generally fast 0.05 to 2.5 secs typical |
Excitation |
None |
Constant current required |
None |
Characteristic |
Thermovoltage |
PTC resistance |
NTC resistance (some are PTC) |
Linearity |
Most types non-linear |
Fairly linear |
Exponential |
Lead resistance effect |
Short cable runs satisfactory |
3 & 4 wire – low. 2 wire – high |
Low |
Electrical “pick-up” |
susceptible |
Rarely susceptible |
Not susceptible |
Interface |
Potentiometric input. Cold junction compensation required |
Bridge 2,3 or 4 wire |
2 wire resistance |
Vibration effects/ shock |
Mineral insulated types suitable |
wirewound – not suitable. Film – good |
Suitable |
Output/ characteristic |
From 10µV/°C to to 40µV/°C depending on type |
approx. 0.4 W/°C |
-4% / °C |
Extension Leads |
Compensating cable |
Copper |
Copper |
Cost |
Relatively |
Wirewound – more expensive Film – cheaper |
Inexpensive |
Comments and values shown in this chart are generalised and nominal. They are not intended to be definitive but are stated for general guidance. |