Various thermometer and it's working principles

1.  The following characteristics can be used to measure the
temperature
 A change in dimentions-expansion or contraction of material
written as temperature change
 A change in electrical resistance of metals and semi-
conductors written as temperature change
 A thermo-electric emf produced due to temp difference at
two junction of two metal alloy joined together
 A change in intensity and colour of radiation emitted by the
hot body written as to change in temperature

2.  Temperature is a measure of the thermal energy in the body.
Normally measured in degree [°] using one of the following
scales.
1) Fahrenheit.[°F]
2) Celsius or centigrade.[°C]
3) Kelvin.[°K]

3.  Introduction :
• Pressure spring thermometer are three types
1) liquid expansion thermometer
2) gas expansion thermometer and
3) vapore actuated thermometer
 The construction and mechanical operation of all type of
pressure spring thermometer contain a metal bulb, capillary and
receiving element. Metal bulb contain a thermometer fluid, a
liquid or a gas or a liquid vapour and is inserted at the ponit at
which the temperature is to be measured. The bulb comes in
thermal equilibrium with its surrounding, thereby developing a
given pressure or displacement of fliud.

4.  A metal capillary is connected to the bulb and transmit the
pressure at the bulb to the receiving element at the
instrument. The reciving element is a form of bourdon tube or
pressure spring. It is used to convert the pressure of
displacement of fliud in the thermometer bulb into a motion.
This motion is used to operate a pointer for the indication of
temperature.

6.  The bulb is filled with the thermal liquid at a high pressure. A
temperature increase at the bulb result in an expansion of the
liquid which causes expansion of the bourdon tube or
pressure spring and thus indicates the temperature. Mercury
is most widely used thermal liquid because of its wide
temperature range. Ethanol or toluene may also be used. The
thermal expansion of the liquid is about six times grater than
that of mercury and from that standpoint their use is
advantageous. The temperature limits of the mercury filled
pressure thermometer are about-35 to 1000F.

7. 1) Greater sensitivity
2) Linear scale shape
3) No head effect
4) No barometric effect

8. 1) Immersion effect
2) Ambient temperature effect