Basically THERMISTOR is a type of TRANSDUCER , which changes its resistance with change in temperature.

TRANSDUCER , a device , which converts one form of energy into another form.Following are some examples which will give an idea about TRASDUCER. 1. Galvanometer 2. Microphone 3.Loudspeaker 4.LDR 5.Quartz crystal 6.Solar cell 7.Thermistor

In industries , mostly transducers are used to convert non electrical quantity in electrical quantities.

TRANSDUCERS

Passive transducers(externally powered)

Active transducers(self-generating)

e.g. LDR , thermistor

e.g. Thermocouple , solar cell , piezo electric effect

THERMISTOR:- Thermistor is a temperature transducer & it belongs to passive type of transducer group , it can not generate self energy. It must be operated with an DC power supply.

BASIC PRINCIPLE:-

Thermistor is a transducer which changes its resistance when its temperature changes. basically , it has two types 1.PTC(Positive temperature co-efficient) 2.NTC(Negative temperature co-efficient) usually , thermistor has high negative temperature co-efficient of resistance.

Construction: Thermistor is a semiconductor device; it can be of NTC or PTC type . Usually NTC type is preferred than PTC . In NTC type resistance decreases with increase in temperature . In case of some thermistors it is about 5 to 6% per c. they are very sensitive & widely used in industries for temperature measurement & in temperature control system.

Thermistor is capable of producing electrical variation when stimulated by some physical form of energy, & which does not require external power supply to perform its function.

They are also known as temperature sensors , they are used for measuring temperatures. Thermistor is composed of a sintered mixture of a metal – oxides like Mn,N,Co,Fe and uranium.

They are available in different packages such as disk type , washer type , bead & bulb type. Bead type thermistors are more popular having diameter about 0.15 mm. Diameters of other types are about from 2.5 to 25 mm.

1.Small in size & low cost.2.Comparatively large change in temperature for a given change in temperature.3.Fast response over a narrow temperature range.

1.The resistance versus temperature characteristic is highly non-linear.2.Not suitable over a wide range of temperature.3.Because of high resistance of thermistor , shielded cables have to be used to minimize interference.4.Requires whetstone bridge circuit & external power source for measurement.

Advantages of Thermistor

Disadvantages of Thermistor

Typical range of thermistors is from 0.5Ω to 100 MΩTemperature range is from -100 to 300

APPLICATIONSThermal transducers commonly used in verity of application such as:1.Thermometer2.Temperature controlled soldering iron.3.Gas detector.4.Furnace control.5.In different temperature regulators.

THANK YOU…..

Ani…