Introduction

A temperature sensor is a device that gathers data concerning the temperature from a source and converts it to a form that can be understood either by an observer or anther device. It measures the temperature of a medium. The sensors are used for different purposes from the simple home use to extremely accurate and precise scientific use.

The best well known example is mercury-in-glass thermometer. The mercury in the thermometer expands and contracts on the change in temperature. As the volume change is quantified the temperature is measured with a fair degree of accuracy. These temperature sensor are used from home to the university labs for the temperature measurement.

The complex temperatur sensors are computerised  for gettig more accurate results . These devices have typically two forms> contact sensors and non contact sensors.

Even human and most animals  have biological temperature sensors in their body which works as the same function as the artificial does. It collects data and transfers it into a understandable form. For eg, human sensory nerves sends sensory information from the skin to the brain in the form of electrical impulses. 

Types

Types: Temperature Sensors measure the amount of heat that produces from the object. It detects the changes of the temperature either as output of analog or digital. The temperature consists of two basic types of features:

• Contact Temperature Sensor Types – These types of sensors are needed to be in contact with the object or system that is to be measured. They can measure solid, liquid or gas in a wide range.
• Non-contact Temperature Sensor Types – These types of temperature sensor use convection and radiation to measure temperature. They can measure liquid or gaseous state of object that emits radiant energy in the form of infra-red radiation.

These two basic types of sensors can be sub-divided into the following three groups of sensors, Electro-mechanical, Resistive and Electronic. All these are discussed below:

The Thermostat: This is a type electro-mechanical temperature sensor, which is consists of two different types of metal; for example nickel, copper, tungsten or aluminum. These are bonded together to make a bi-metallic strip. When this is connected with heat, the different linear expansion of two different metals produces a mechanical bending.

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The thermostat consists of two thermally different metals. When this is connected with cold object, the two metals are closed together and current passes through the thermostat. When it gets hot, one metal expands more than the other and the bonded bi-metallic strip bends up (or down) opening the contacts preventing the current from flowing.

There are two main types of bi-metallic strips, which change their expansion according to temperature changes of the object. These are “snap-action” and “creep-action”. The “snap-action” types give instantaneous action “ON/OFF” or “OFF/ON” on the electrical contacts at a set temperature point, and the slower “creep-action” types that gradually change their position as the temperature changes.

Snap-action type thermostats are commonly used in our homes for controlling the temperature set point of ovens, irons, immersion hot water tanks and they can be found on walls to control the domestic heating system. But it has large hysteresis range on the opening and closing of electrical contracts. That’s why commercially available bi-metallic thermostats have temperature adjustment screws, by which it is possible to adjust the temperature at desired level and pre-set hysteresis level.

Application:

references:

http://www.electronics-tutorials.ws/io/io_3.html

https://controls.engin.umich.edu/wiki/index.php/TemperatureSensors