What is an RTD ? How RTD Works ?

In this Article, we will discuss what is an RTD, and how it works.

The term RTD stands for resistance temperature detector RTD is a temperature sensor that is used to measure temperature by associating the resistance of the RTD element with temperature

RTD is a passive device, external electronic devices are used to measure the resistance of the sensor by passing a small electrical current through the sensor,

working principle.
Every material has atoms in it, and all atoms have some energy due to it. It vibrates slightly.

When a battery is connected to a conductor current flows through the conductor. Since the flow of current is due to the flow of electrons.

These electrons frequently collide with vibrating atoms of the conductor, these collisions decrease the speed of the electrons.

This property of a material, due to which it opposes the flow of current through it is called resistance. Now when we heat the conductor, the atoms of the conductor absorbs heat energy. As a result, their vibration increases. Because of this increase in vibration, the collision of electrons with atoms also increases. And so it becomes very difficult for electrons to move across the conductor and hence the resulting output current decreases and RTD works on this principle of measurement, which states that the resistance of a material changes with temperature. As the temperature of the metal increases the metals resistance to the flow of electricity also increases.

Parts of RTD

1.sensing element or RTD element.

The sensing element is the actual temperature sensing unit, which is located at the tip of the temperature sensor on the end that is express to the process temperature,

the sensing element, which is constructed of metals like Platinum nickel copper or tungsten respond to the process temperature by generating a measurable resistance lead wires


lead wires are attached to the sensing element, and then pass through the sensor sheet

lead wires connect the sensing element, either directly to the DCS, or to a Temperature Transmitter connected to our DCs sensor sheet. The sensor sheet is constructed of metal and hauls

most of the component parts of the temperature sensor. The sensor packing typically magnesium oxide surrounds

the sensing element and is contained within the sensor sheet. The sensor packing decreases the impact of process vibration on the sensing element, and thus ensures a more accurate measurement threaded adapter,

the threaded adapter is welded over the rear housing of the sensor sheet, one end of the threaded adapter threads into a thermo well or directly into the process piping. The other end is typically threaded into a Temperature Transmitter working of RTD.

Suppose we want to monitor the temperature of an oven. To do this work, the probe of an RTD is inserted into the oven.

Due to the temperature of the oven, the resistance of the sensing element of the RTD varies correspondingly the RTD gives output of resistance in ohms. But that is not a standard signal that can be transmitted into the control room. So we have to convert that change in resistance to a change in voltage and this can be done using Wheatstone bridge.

These Wheatstone bridge cures are built into the transmitter PLC DCS or PID controller

RTD may be located hundreds of feet away from that bridge so cute.

Two types of Wheatstone bridge circuit configurations are mainly used.

One is now balanced bridge, and the other is deflection bridge in narrow balance rates, the resistors R1 and R2 and R3 is an adjustable resistor,

the resistor R three is initially adjusted in order to obtain zero volt in the voltmeter in this condition.

The bridge is said to be well balanced.

This would be the zero or setpoint on

the RTD temperature output as the RTD is inserted into the oven,

the RTD temperature increases and correspondingly the voltage indicated by the volt meter also increases in deflection bridge, all three resistors are fixed, and not adjusted and output voltage varies, corresponding to the temperature of RTD. If a voltage transducer replaces the voltmeter a 40 to 20 milli amperes signal, which is proportional to the temperature range can be generated.

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