Major Terms used in Temperature measurement
Measure temperature by correlating the the voltage differential between the junction of two different metal alloys and a reference voltage to temperature
Measures temperature by correlating the resistance of a resistive element with the temperature
Converts the low-level signal generated by one of these temperature sensor types and converts it into a higher power level (4-20 ma) signal that can be transmitted over long distance
What is thermocouple ?
Most popular type of temperature sensor.
Can measure wide range of temperatures
Are interchangeable and have standard connectors
Two thin metal wires welded together to form a junction.
Almost any type of metal can be used.There are preferred metal used for their predictable output voltages and ability to withstand large temperature gradient.
How Thermocouple works ?
The junction between two metals generates a voltage that is a function of temperature.This is know as thermoelectric or seebeck effect.
The picture shows two different metal alloy leads welded together to form a thermocouple juction.
The differential is measured and compared with the known voltage/temperature relationship to determine the temperature of the environment being measured.
It is not possible to simple measure the voltage differential directly and the metal leads of a voltmeter would create an addition thermocouple junction.
A thermocouple output also nonlinear complex polynomial equation.
Types of Thermocouple.
Thermocouple are made from different metal alloy pairs which all have different characteristics such as temperature range and accuracy.
Thermcouple comes as either:
Bare wire bead which is low cost
Built in to probes such as needle,insulated,catheter,capsule,direct immersion,surface mount, and micro thermocouple.