BASIC PRINCIPLE :
when a bimetallic thermometer at one end is fixed to other end is free is subjected to the temperature change the free end of the bimetallic helical deflection is proportional to the change in temperature this deflection becomes a major of the change in temperature
DESCRIPTION :
The main parts of a helical bimetallic thermometer are as follows
----> A bimetallic helical which is fixed at one end.to the body of the instrument and free at its other end to the free end of bimetallic helical is attach a shaft
----> one end of the shaft is mounted in a frictionless arrangement and its other end is connected to a pointer which sweeps over a temperature calibrated circular dial in degree of temperature
WORKING :
----> when the temperature of medium is to be measured the bimetallic thermometer is introduced into the medium for a length
----> the bimetallic helical sense the temperature and. expands resulting in a deflection at its free end
----> this deflection at its free end of the bimetallic helical rotate the shaft connected to it
----> when the shaft rotates the pointer attach to the shaft moves to new position on the temperature calibrated dial indicating the measured temperature
APPLICATIONS :
It is used in control devices the helical strips is used for process applications such as oil burner, refiners, the spiral strips is used in conditioning thermostat
ADVANTAGES :
----> They are simple in design and inexpensive
----> they can withstand 50%over range in temperature there accuracy is 2%-5%
DISADVANTAGES :
----> they are not recommended for above 400 temperature
----> when regularly used the bimetallic may be permanently deformed and will introduce error
SPIRAL BIMETALLIC THERMOMETER
BASIC PRINCIPLE:
when a bimetallic spiral thermometer at one end is fixed and other end is free is subjected to the temperature.change the free end of the bimetallic spiral deflection is proportional to the change in temperature.this deflection becomes a major of the change in temperature
CONSTRUCTION :
»» the main part of a spiral bimetallic thermometer are as follows
»» the spiral bimetallic thermometer which is fixed at one end to the body of the instrument and free at its other end to the free end of spiral bimetallic is attach to a shaft
»» one end of the shaft is mounted in a frictionless arrangement and its other end is connected to a pointer which sweeps over a temperature calibrated circular dial in degree of temperature
WORKING :
»» when the temperature of medium is to be measured the spiral bimetallic thermometer is introduced into the medium for a length
»» the spiral bimetallic thermometer sense the temperature and expands resulting in a deflection at its free end
»» this deflection at the free end of the spiral bimetallic rotate the shaft connected to it
»» when the shaft rotates the pointer attach to the shaft moves to the new position on the temperature calibrated dial indicating the measured temperature
APPLICATIONS:
»» it is used in control devices
»» they are used in oil burner and refiners, thermostats
ADVANTAGES :
»» the design is complicated and they are expensive
»» they can withstand upto 80%over range in temperature
»» the accuracy is between 3%-8%
DISADVANTAGES :
»»they are recommended for high temperatures above 800
»» continuous will not effect the spiral bimetallic thermometer
You must be logged in to post a comment.