Bimetallic thermometer

Bimetallic Thermometer ppt giving basic idea abt construction working and types of the same

1. Bi-Metallic Thermometer Introduction History Principle Construction Working Advantage Disadvantage Applications References

2. INTRODUCTION The accurate measurement of temperature is vital across abroad spectrum of human activities. Including industrial processes , Manufacturing Monitoring(in food transport and storage) Health and Safety In fact in almost every sector temperature is one of the key factor to be measured.

3. THERMOMETER The word thermometer comes from Greek words thermos meaning “hot” and meter meaning “measure”. A thermometer is a device that measure temperature or temperature gradient. A thermometer has two important elements. a) A temperature sensor in which some changes occur with change in temperature. b) Some means of converting this change into a numerical value. Thermometers are widely used in industries to monitor processes, in scientific research etc.

4. Temperature Scale

5. Bimetallic Thermometer In an industry there is always a need to measure and monitor temperature of a particular spot, field or locality. The industrial names given to such temperature sensors are temperature indicators or temperature gauges. All these temperature gauges belong to the class of instruments that are known as bimetallic sensors.

6. HISTORY The earliest surviving bimetallic strip was made by the eighteenth century clockmaker John Harrison who is generally credited with its invention. His earliest example had two individual metal strips joined by rivets but he also invented the later technique of directly fusing molten brass onto a steel substrate.

7. WORKING PRINCIPLE Two basic principles of operation is to be followed in the case of a bimetallic sensors. 1. A metal tends to undergo a volumetric dimensional change(expansion/contraction), according to change in temperature. 2. Different metals have different co- efficient of temperature. The rate of volumetric change depends on this co-efficient of temperature.

8. CONSTRUCTION The device consists of a bimetallic strip of two different metals. Each metal of thermometer has different thermal expansion coefficient. They are bonded together to form a spiral or twisted helix. Both these metal are joined together at one end by either welding or riveting. It is bonded so strong that there will not be any relative motion between the two.

9. INDUSTRIAL BIMETALLIC THERMOMETER

10. WORKING The bimetallic thermometer uses the bimetallic strip which coverts the temperature into the mechanical displacement. The working of the bimetallic strip depends on the thermal expansion property of metal. The thermal expansion is the tendency of the metal in which the volume of metal changes with the variation in temperature. When the temperature increases , the strip bends towards the metal which has a low temperature co-efficient.

11. WORKING When the temperature decreases, the strip bends towards the metal which has a high temperature co-efficient. The range of deflection of bimetallic strip depends on the type of the metal used for construction. The deflection is directly proportional to length of strip and the variation of temperature and is inversely proportional to the thickness of the strip.

12. DIAGRAM

13. METALS USED IN BIMETALLIC STRIP High expansion Yellow brass Nickel(iron alloy with chromium and manganese) Low expansion Invar(alloy of nickel and iron) Iron

14. RADIUS OF CURVATURE OF BS

15. ADVANTAGES The bimetallic thermometer has good accuracy. Wide ranges are available. The bimetallic thermometer is easily installed and maintained. The cost is very low. They are fully mechanical devices no need of power sources. These thermometer works best at higher temperature.

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

17. APPLICATIONS Clocks Thermostats Thermometer Electrical devices Heat engines

18. REFERENCES https:// www.mechgrid.com/bi-metallic-mechanical-thermometer-and-applications.html https://www.polytechnichub.com/advantages-disadvantages-bimetallic-thermometer / https:// circuitglobe.com/bimetallic-thermometer.html https:// automationforum.in/t/how-a-bimetallic-thermometer-work/3932

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