63. Temperature Measurement

yaboiemil's version from 2016-02-03 20:19

General Knowledge of Temperature


1, The Kelvin scale of temperature is a scale independent of any thermal medium. (e.g. Water)
2. The triple point of water is the temperature at which ice/water/vapor states are at equilibrium.
3. The ice point of water is 273K
4. 1 Kelvin is equal to 1/273 of the triple point of water.
5. The everyday unit of measurement is Celsius. Water freezes at 0C and boils at 100C. (at 1atm)
6. With Fahrenheit, water freezes at 32F and boils at 212F.

Mercury Thermometers


7. Mercury thermometers work because mercury expands its volume at different temperatures.
8. The greater the reservoir and the smaller the capillary diameter, the greater the sensitivity.
9. There is a narrowing right above the reservoir to prevent immediate change to a reading as it
is removed from the patient, This ensures the reading last for 3-5minutes.

Bimetallic Thermometer


10. A bimetallic thermometer is a thermometer created from 2 different pieces of metal that are
stuck together. They bend at a certain temperature, as one gets longer than the other.

Thermistors and thermocouples


11. A thermistor is a semiconductor component with a thermal dependance of resistance.
12. As materials get warmer, they are more able to conduct electricity. This is because as they
heat up, they increase their numbers of free electrons.
13. Thermocouples are creates when 2 identical conductors made from one metal are connected
by a bridge made from a different metal.
14. If the 2 conductors are held at 2 different temperatures, a thermoelectric charge will arise
between them.
15. One is usually kept at a reference temperature.
The voltage depends on the difference between the 2 temperature, as well as the thermoelectric
coefficients of the metals used.


ADVANTAGES: Instantaneous temperature measurement
DISADVANTAGES: Reference temperature is needed.

Contactless Temperature Measurement

16. Contactless temperature measurement is based on the detection of electromagnetic infrared
radiation emitted from the body.


(Related laws are Wien's Shift Law and Stefan-Boltzmann' Law)