Working of Platinum Resistance Thermometer

Normally thermometer is used by the doctor to measure the body temperature.

If a person feels ill and goes to the doctor. then the doctor measures her body temperature by the thermometer.

The temperature range of Clinical thermometer is about to .

But, if we are going to measure the temperature in industry which ranges from to .

Then, we have to use a different type of thermometer to measure the temperature.

Resistance Temperature Detector (RTD) is one such device to measure high temperatures accurately.

RTD measures the temperature by measuring the electrical resistance of wire.

That wire can be of copper, platinum or nickel. but, platinum is predominantly used.

When Platinum is used in RTDs, it is called the Platinum Resistance Thermometer.

The thermal properties of Platinum make is most suitable to be used in RTDs.

The variation of resistance with temperature in a platinum wire is approximately linear as compared to copper and nickel.

So, it is easier to find the variation of resistance with temperature in a platinum wire.

platinum wire is extremely stable, unreactive metal and can easily be drawn into fine wires.

It has a very high operating temperature and give a very high accurate reading.

The basic principle behind platinum resistance thermometer.

Since resistance increases linearly with temperature. So, we have to identify resistance at a particular time.

To identify resistance, we have to pass the current through the platinum wire.

Now, with increasing time platinum element heat up and resistance would increase.

Now, resistance is calculated after taking the reading of voltmeter (V) and ammeter (I).

after getting the value of resistance (), the temperature is calculated by formula given.

and are the resistance of platinum wire at and respectively.

Let's see, how does platinum resistance thermometer work.

Platinum wires wrapped around a core made of ceramic.

When the switch is ON, the current flows through the platinum wire.

And, the platinum wire is heated up and so its resistance increases.

Now, let's see how the resistance of the platinum wire varies with temperature.

When the temperature is low, the platinum atoms vibrate with very less amplitude.

Now, electrons can pass very easily through the gap between platinum atoms and reach the positive side of the terminal.

But when the temperature increases, the thermal oscillation of platinum atoms also increases.

Now, a lesser amount of electrons can reach the positive terminal.

Hence, the current flow decreases, because the current flow is the flow of electron. Therefore, resistance is greater at higher temperature.

Hence, when the temperature of the platinum wire is increased, the value of resistance is also increased.

and on that resistance, the temperature is calculated with the help of above formula.


Platinum resistance thermometer measures the temperature by measuring the electrical resistance of the wire.

the flow of electron is depends on thermal vibration of platinum atoms which increases with the temperature.

The End