The Sensors

Our range provides two alternative types of temperature sensor - thermocouple or platinum resistance thermometer (PRT).

General guidance for choosing between the two Thermocouples are less expensive than PRT sensors, more versatile, less accurate, more rugged, more sensitive, have a wider operating range, are tip senitive and can be smaller. Extension cabling is more expensive. Various calibrations are available for different applications.

PRT assemblies are much more accurate and stable, permit greater resolution of measurement but over a more limited range, are stem sensitive, larger and more expensive. Extension cabling is by inexpensive copper wire.

Remember the type of sensor chosen must suit the associated instrumentation.

 

Comparison of Sensor Types
V Platinum Resistance Thermometer Thermocouple
Sensor Platinum-wire wound or flat-film resistor Thermoelement, two dissimilar metals/alloys
Accuracy (typical values) 0.1 to 1.0°C 0.5 to 5.0°C
Long term Stability Excellent Variable, Prone to ageing
Temperature range -200 to 650°C -200 to 1750°C
Thermal response Wirewound - slow Sheathed - slow
Film - faster Exposed tip - fast
1-50 secs typical 0.1 to 10 secs typical
Excitation Constant current required None
Characteristic PTC resistance Thermovoltage
Linearity Fairly linear Most types non-linear
Lead resistance effect 3 & 4 wire - min Short cable runs satisfactory (e.g. 25m)
2 wire - error result
Electrical "pick-up" Rearly susceptible Susceptible
Interface Bridge 2, 3 or 4 wire Potentiometric input. Cold junction compensation required
Vibration effects/shock Wirewound - not suitable Mineral insulated types suitable
Film - good
Output/characteristic Approx 0.4 W/°C From 10mV/°C to 40mv/°C depending on type
Extension Leads Copper Compensating cable
Cost Wirewound - more expensive Relatively low cost
Film - less expensive