Thermocouples ANSI

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
low cost

Wirewound – more expensive

Film – cheaper

Inexpensive
to moderate

Comments and values shown in this chart are generalised and nominal. They are not intended to be definitive but are stated for general guidance.