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. |
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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 |