FILLED-SYSTEM THERMOMETER TYPES

o GAS-FILLED THERMOMETERo LIQUID-FILLED THERMOMETERo MERCURY-FILLED THERMOMETERo VAPOUR-PRESSURE THERMOMETER

“LIQUID-FILLED THERMOMETER”

These thermometer are completely filled with a liquid(other then mercury) and operate on the principle of liquid expansion with an increase of temperature.The filling fluid is usually an inert hydrocarbon , such as xylene(C8C10)which has a co-efficient of expansion six times that of mercury and makes smaller bulbs possible.

When we use other liquid , the condition is that the pressure inside the system must be greater than the vapour pressure of the liquid to prevent bubbles of vapour from forming in the spiral.

The liquid should not be allowed to solidify even in storage , otherwise the calibration may be affected.

ADVANTAGES & DISADVANTAGES

• Rugged Condition

• Require low maintenance

• Three or more separate systems can be put

• Cost is low

• No need of electronic power

• Need a large bulb for the sake of accuracy

• The entire system usually has to be replaced in case of failure

• Maximum spans are not as narrow as in the bimetallic thermometer

• They have limited maximum temperature compared to some electrical measurement

ADVANTAGE DISADVANTAGE

THANKY OU