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