The Resistance Temperature Detector (RTD) and Thermistor are the temperature sensitive devices used for the measurement of temperature. The RTD is also called a resistance thermometer is a wire coil made up of metals (platinum, copper, or nickel).
They exhibit a change in resistance when the temperature changes. Whereas a thermistor is a thermal resistor composed of metal oxides. Thermistors are sensitive to small changes in temperature and are capable of measuring small temperatures.
There are two types of thermistors positive temperature coefficient thermistor that exhibit linear characteristics (increase in temperature causes resistance to increase) and negative temperature coefficient thermistor that exhibits non-linear characteristics (increases in temperature causes resistance to decrease).
In RTD there is only a positive correlation between resistance and temperature i.e., the resistance increases as the temperature increases and vice-versa. The various differences between RTD and Thermistor are given below.
Definition of RTD (Resistance Temperature Detector) :
A resistance temperature detector or resistance thermometer is a temperature measuring device. It is basically a conductor wire whose resistance depends upon temperature i.e., variation in temperature causes to vary its resistance. By measuring the variation in resistance, the temperature which causes this change in resistance can be determined.
A fine annealed wire coils made of platinum, nickel, copper, etc are wound or wrapped around insulating support made of ceramic, mica, or glass to have very little physical strain in the presence of temperature variations.
The proper arrangement of wire wounded on the insulating support provides good thermal conductivity and a high heat transfer rate. This complete arrangement is then mounted in a protective sheath which is provided with a waterproofed seal.
Definition of Thermistor :
The thermistor is also a temperature measuring device whose resistance is sensitive to temperature. It is a thermally sensitive device made up of sintering (pressing) mixtures of metallic oxides like copper, nickel, cobalt, iron, manganese, and uranium.
When there is a variation in temperature the resistance of the thermistor changes. This change in resistance is measured and the resistance determines the temperature change.
The thermistor can be of two types according to the variation in resistance with respect to the variation in temperature. They are positive and negative temperature coefficient thermistors.
In a positive temperature coefficient or NTC thermistor, the resistance increases with an increase in temperature. For negative temperature coefficient or NTC thermistor, the resistance decreases with an increase in temperature. But, mostly NTC thermistors are used which exhibits non-linear characteristics.
Difference Between RTD and Thermistor :
| RTD (Resistance Temperature Detector) | Thermistor |
|---|---|
| RTD is a type of wire whose resistance changes with change in its temperature. | A thermistor is a temperature sensitive resistor whose resistance varies with temperature variation. |
| RTD is made of pure metals like platinum, nickel, or copper. | Thermistors are made up of ceramic or polymer materials. |
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| It has a positive temperature coefficient. | It has a negative temperature coefficient. |
| RTD has low accuracy. | Thermistors have good accuracy. |
| Used for greater temperature range up to 600°C. | Used for lower temperatures ranging from -55°C to +130°C. |
| RTD allows smaller cable lengths. | It allows larger cable length. |
| Slow output response. | Fast output response. |
| Used in industrial installation applications. | Used in home appliances. |
| Good stability. | Less stable than RTD. |
| These are expensive. | These are inexpensive. |
| Low amount of self-heating. | High amount of self-heating. |
| The size of resistance therometer is quite large. | Thermistors are build in smaller size with different shapes. |
| It possesses good linear characteristics. | It possesses non-linear characteristics. |