Rtd and thermocouples

April 9, 2023 1

Calibration of Thermocouples and RTD

By:Ashutosh Katti (T3814)Aditya Medhekar (T3827)

Mechatronix seminar

April 9, 2023Mechatronix seminar 2

What is an RTD?

RTD stands for Resistance Temperature Detector.

The change in temperature is detected by the change in resistance of the wire.

There are two types of RTD, viz. having positive and negative thermal coefficients of resistivity (resistance increases or decreases with the increase in temperature respectively).


• RTDs are used for temperature measurements by using them in bridge circuits.

• The change in temperature causes considerable resistance change which gives a voltage drop in accordance with the thermal coefficient of resistance of the wire.

• This voltage is further amplified and the temperature is read thus. This is how the RTDs are used in circuits assisting in automatic control and measurement with high accuracy.


Advantages

Due to no fluid present absolute temperature is recorded.

It is highly sensitive and gives accurate results.

It has a good range of temperature measurement. It can thus

measure from very low to very high temperature.

Due to electrical output (resistance change) it can be used with

PLCs and complete automation can be achieved.


Applications of RTD

It is widely used in furnaces for automatic temperature

measurement.

Due to its compactness, it replaces conventional

thermometers as well as thermocouples thus eliminating

the use of lots of wires.

Used in medical and chemical laboratories to detect very

low temperatures (like dry ice and liquid nitrogen).

Due to electrical output it is used wherever feedback

system is required and corrective action is thus taken in an

automated system.


What are thermocouples?

• Thermocouples are metal couples which work on the

Seebeck effect.

• In this effect, any conductor is subjected to a thermal

gradient, it will generate a voltage.

• Measuring this voltage necessarily involves connecting

another conductor to the "hot" end. This additional

conductor will then also experience the temperature

gradient, and develop a voltage of its own which will

oppose the original.


Types of thermocouples

There are about 4 to 5 types of thermocouples which are

categorized based on sensitivity and range.

• J and K type thermocouples are noted for their high sensitivity.

These however, have a limited range. (about 41µV/˚C for K

and 55µV/°C)

• Platinum Types: The B, S, T and R type of thermocouples are

less sensitive (about 10µV/˚C) but they have a very significant

advantage of high range. They can measure large

temperatures and are usually used in furnaces.


Thermocouple sensors

• Sensitivity: It is the voltage or emf produced per degree

Celsius rise or fall in temperature at the junction.

• Construction: Simply welded or twisted between 2 metals.

• Range: Thermocouples have the greatest range in all types of

temperature measurement instrument domains.


• Time Response: It is the time required by the

thermocouple to reach thermal equilibrium with the

surrounding. Industrial TC using thick wire have lower

response of about 20s however, TCs of small gauge wires

have response time of about 20ms.

• Signal conditioning: the output voltage from the

thermocouples is very small usually less then 50 mV. Thus

considerable amplification is required so as to be used for

practical applications


OVEN

RTD TC Temperature indicatorON/OFF controller

230V AC50 Hz

Switch

RTD and Thermocouple Calibration Setup


THANK YOU!

Rtd and thermocouples

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