This document discusses different types of filled-system thermometers, including liquid-filled thermometers. Liquid-filled thermometers are completely filled with a liquid other than mercury and operate based on the principle of liquid expansion with increasing temperature. Common filling fluids are inert hydrocarbons like xylene. The liquid should not be allowed to solidify and the pressure inside must be greater than the vapor pressure to prevent bubbles from forming. While rugged and low-cost, liquid-filled thermometers have limitations such as needing replacement of the entire system if a failure occurs and having wider measurement spans than bimetallic thermometers.

1. FILLED-SYSTEM THERMOMETER
 TYPES
o GAS-FILLEDTHERMOMETER
o LIQUID-FILLED THERMOMETER
o MERCURY-FILLED THERMOMETER
o VAPOUR-PRESSURE THERMOMETER

2. “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

3. 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.

4. 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