## Instrumentation

### How to check RTD

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• In this lesson, we will study How to check RTD.
• Resistance temperature Detector as the name indicates Detects Temperature and gives the output as resistance.
• The short form of Resistance Temperature Detector is RTD.
• RTD is a Temperature Sensor.
• Resistance Temperature Detectors (RTDs) give a linear change in resistance with respect to temperature.
• RTDs are a positive temperature coefficient. i.e. Resistance increases with an increase in temperature.
• Platinum is Commonly used in RTDs because its temperature Resistance characteristic is more linear in comparison to copper and nickel.
• RTD types are broadly classified according to the different sensing elements used.
• Platinum, Nickel, and Copper are the most commonly used sensing elements.
• Platinum is considered the best as it has the widest temperature range. This is shown in the resistance versus temperature graph below.
• Platinum type RTD is also known for its best interchangeability than copper and nickel. It also has the highest time stability. How to check an RTD

• There are three wires in RTD. Out of the two wires are short-circuited as shown in the figure. The same color wires are short-circuited. • In the above figure, blue colour wires are short-circuited.
• The different colour wire will show the same resistance with other same colour wires.
• Now the resistance will be calculated by using the following formula

Rt=R0(1+@T)

Where Rt is resistance at T degrees Celcius.

R0 is the resistance at 0 degrees Celcius.

T is the temperature that we need to calculate.

@ is alpha that is temperature coefficient. Value of Alpha is .0385 for Platinum.

Now for PT 100 temperature will be Calculated by using formula

### [( Resistance Shown by Multimeter- 100)/0.385] • 35
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