Instrumentation and Sensors Package

// (ou blink)


Temperature Measurement

Temperature Sensors


made out of two strips or wires of different metals (alloys) and joined at one end. The joint is called

thermo-junction. A thermocouple produces voltage as a function of temperature. The voltage generated rises

with temperature although it is not linear. A thermocouple does not need power to operate thus it is a passive


Thermocouple leads are color coded. In the U.S. the color code is Red

and some other color, where the red lead is the negative (low) lead.


Take Care for other countries

Every time you connect two different metals/alloys a thermocouple

junction is formed.










Dealing with Thermocouples

You cannot extend a short thermocouple wire using a regular wire or

using a different type of thermocouple to make a longer thermocouple


Connecting a thermocouple wire to an instrument in reverse will not

harm the instrument. It will however give you an incorrect reading.

RTD and Thermistor

RTD (Resistance Temperature Detector) is made out of metal

(Platinum wire wrapped around a mandrel and covered with a

protective coating)

Thermistor is made out of ceramic semiconductor.


RTD and thermistor are both non-linear

RTD/Thermistor Circuit

A fixed, DC current is supplied to the sensor, the voltage developed

across the sensor is a function of temperature.

Measure Voltage Here


Constant Current Source

Infrared Thermometry

non-contact temperature sensor. It senses the amount of radiated

energy, in the infrared band, by the targeted object.

You must know the emissivity of the surface being measured in order

to be able to measure its temperature correctly.

The emissivity of a material is normally listed in a table that comes

with the instrument.

If you don't know the emissivity of the surface you are targeting, you

can put a masking tape on the surface and use 95% as the emissivity

number. This approach won't work in a gin stand, will it? You can

"fudge" the emissivity number by using another instrument to

measure the temperature and then use the infrared to measure the

same temperature and make the readout correct by trying different

emissivity numbers.