Thermocouples and rtd Prepared By: Ansari Najma A. (130480109002) Patel Jainali J. (130480109028) Patel Payal U. (130480109036) Patel Rimpal B. (130480109038)

What is 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 41microvolt/ ‘c for K and 55microvolt/’c) Platinum types: The B, S, T and R type of thermocouples are less sensitive (about 10microvolt/’c) but they have a very significant advantage of high range. They can measure large temperatures and usually used in furnaces.

Thermocouple sensors It is the voltage or emf produced per degree celsius rise or fall in temperature at the junction. Simply welded or twisted between 2 metals. Thermocouples have the greatest range in all types of temperature measurement instrument domains. It is the time required by the thermocouple to reach thermal equilibrium with the surrounging. industrial TC using thick wire have lower response time of about 20ms. 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.

RTD and Thermocouple calibration setup

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 the wire.

This voltage is further amplified and the temperature is read thus 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.

Application of RTD It is widely used in furnaces for automatic temperature measurement. Due to its compactness,it replaces conventional thermometers as well as thermocoupled thus orieseliminating the use of lots of wires. Used in medical and chemical laboratories to detect very low temperature (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.

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