Pressure swing thermometer

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 Temperature measurement

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

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 . PRESSURE-SPRING THERMOMETER

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.

5. Figure :

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. Working :

7. Greater sensitivity Linear scale shape No head effect No barometric effect Advantages :

8. Immersion effect Ambient temperature effect Disadvantages :

9. Thank you