Instrumentation and SensorsPackage
Objectives of the sub-package
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
Thermistor is made out of ceramic semiconductor.
RTD and thermistor are both non-linear
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
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