bimetallic strip

bimetallic strip

1. BIMETALLIC STRIP THERMOMETER Presented by NAME : S.ARUNKUMAR DEPARTMENT : MECHANICAL ENGINEERING COLLEGE : SUDHARASAN ENGG COLLEGE

2. CONTENTS Introduction Types Construction Working & Principle Advantages & Disadvantages Applications

3. INTRODUCTION A Bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass. The different expansions force the flat strip to bend one way if heated and in the opposite direction if cooled below its initial temperature.

4. TYPES

5. CONSTRUCTION The temperature is measured by means of a bimetal system inside the bimetal strip. The bimetal is made from two metal strips, each metal having a different thermal expansion coefficient. The stripes are permanently joined by means of welding or riveting etc

6. WORKING Two basic principles of operation is to be followed in case of a bimetallic sensor. A metal tends to undergo a volumetric dimensional change (expansion/contraction), according to the change in temperature. Different metals have different co-efficient of the thermal expansion. The rate of volumetric change depends on this co-efficient.

7. METAL USED HIGH EXPANSION Yellow brass Nickel iron alloy with chromium and manganese LOW EXPANSION Invar (alloy of nickel and iron) iron

8. ADVANTAGES They are simple, robust and inexpensive. Their accuracy is between 2 to 5% of the scale. They are fully mechanical devices no need o power source. These thermometers work best at high temperature.

9. DISADVANTAGES They are not recommended for temperature above 400 degree celsius. When regularly used, the bimetallic may permanently deform, which in turn will introduce occurs. Their sensitivity and accuracy is less at low temperature.

10. APPLICATIONS Iron box Fire alarm Thermostat