sorces of errors in a filled system thermometer

Presented By :

Tejas Atyam

4th sem Production

Common Sources of Errors are:

Ambient temperature Effect

Head or Elevation Efffect

Barometric Effect

Immersion Effect

Radiation Effect

The effect taking place due to the

exposure of the bourdan tube and the

capillary tube to the surroundings .

Being exposed to the surroundings causes

them to be subjected to variable temp.

widely different to that of the bulb .

Using Large Bulb :

From the equation we can clearly see that

the use of a larger bulb will reduce the

error

Case Compensation :

A bimetallic strip or secondary bourdan

tube is used to counter the deflection in

the main bourdan tube in the opposite

direction .

Full Compensation :The only new difference id that even a capillary tube has been attached to counter the effects .

Using Self Compensating Capillary :In this case the cross section of the capillary is made into a annulus which has a special alloy wire in its whole length to counter the capillary expansion.

This is the error caused due the elevation

of the bulb from the level of the bourdan

tube . Due to the difference in height a

pressure head is created which causes

error in the temperature reading .

The tip travel of bourdon tube is due to

pressure difference between atmosphere

and filled system pressure . So if there is

any variation in atmosphere pressure from

designed pressure , the bourdon tip travels

and causes an error reading .

The equation shown by me is used to

calculate the error .

This error is caused to the improper

immersion or insulation of head of bulb .

This error occurs due to temperature difference between the bulb and solid bodies around it .

Dip Effect : In case of a metallic bulb of mercury filled system, the metallic bulb expands before expansion of mercury , hence volume of bulb is increased and pressure reduces . So in short respose of thermometer is slowed down .