THERMISTOR

Thermistor are a temperature measurement device that has a negative temperature coefficient. As the temperature increases the resistance decreases and temperature decreases the resistance increases. Thermistors are made from semiconducting materials mixtures of metallic oxides such as chromium, nickel, cobalt, copper, iron, etc. There are two main type Positive temperature coefficient (PTC) and Negative temperature coefficient (NTC).  

THERMISTOR TYPE:-

l  In positive temperature coefficient thermistor then resistance increases with increases temperature.

l  In negative temperature coefficient thermistor then resistance decreases with increases temperature. 

CCONSTRUCTION:-

                                      Thermistor are composed of sintered mixture of metallic oxides such as manganese , nickel cobalt, copper, iron, and uranium. The mixture of these materials is pressed into different shapes and size like  is beads, washer, disk, flake and rod type. A thermistor is placed in contact with the media whose temperature is to be measured.

WORKING PRINCIPAL:-

                                           It is the principle of it’s resistance is depend upon temperature. When temperature changes, the resistance of the thermistor change in a predictable way.The benefit of using thermistor is accuracy and stability.  A thermistor  is a temperature sensor constructed of semiconductor material. Thermistor are inexpensive, rugged, reliable and responds quickly. Because of these qualities thermistors are used to measure simple temperature measurements, but not for high temperature. Thermistor is easy to use, cheap, durable and respond predictivly to a change in temperature. 

ADVANTAGES:- 

·         Thermistors have a relatively large but negative resistance change.

·         The range for resistance is much greater being -160 to 600C.

·         It is more stable.

·         It has small size and compact.

·         It give good response time fraction of seconds to minutes.

DISADVANTAGES:-

·         It requires external energy source.

·         Unsuitable for a wide range.

·         It is also relatively fragile, so they must be handle and mounted

·         carefully to avoid damage.

·         It is not suitable for higher temperature.

APPLICATION:-

                                PTC THERMISTOR –

·         It is used as fuse for short circuit and over current protection.

·         They are used as a switch for motor start degaussing.

·         They are used as level sensor and limit indicator.

·         They are used as a temperature sensor  in measurement and  control and over protection.

                               NTC THERMISTOR –

·         is also used in industrial application such as industrial control, solar energy equipment, etc.

·         It They are used in consumer/ household appliance like refrigeration, air conditioning, fire detection, etc.

They are used in medical appliance