What are the disadvantage of clinical thermometer?
Answers
Various types of temperature sensors are listed in Section 3.1. They are:
Mercury thermometer
Alcohol thermometer
Bimetallic thermometer *
Resistance thermometer
Thermocouple
Radiometer
Various thermometers are used in different situations. For instance, mercury thermometers are the standard equipment at surface weather stations, and bimetallic thermometers are used in radiosondes. Thermocouples are used for in situ observations at locations wired to a computer network. Radiometers are used for remote observations.
The table below compares the various thermometers.
advantages
disadvantages
Mercury thermometer
cheap
display is harder to read
durable
does not work below -39�C (Hg freezing pount)
accurate
cannot be used for thermograph
easily calibrated
slow response
fragile
mercury vapour is poisonous
Alcohol thermometer (compared to a mercury thermometer)
lower freezing point (-114 �C)
less durable (alcohol evaporates)
larger coefficient of expansion
alcohol can polymerise
less hazardous
fluid loss by evaporation hard to avoid
lower boiling point (60 �C)
Bimetallic thermometer *
cheap
requires frequent calibration to maintain accuracy
durable
fairly slow response
can be used for thermograph
easily calibrated
Electric resistance thermometer
display is easy to read
tends to 'drift' after years of use
rapid response
expensive
accurate over broad temperature range
Thermocouple
display is easy to read
ancillary equipment is expensive
durable
hard to calibrate
can measure temperature variations over a distance of less than 1 cm
measures only a temperature difference
rapid response
Radiometer
allows remote measurements
very expensive
material of emitting surface needs to be known
affected by absorption/emission between object and radiometer
* Temperatures can be measured cheaply by means of the bending of a strip of 'bimetal', made by rolling different metals together, choosing metals which have very different degrees of expansion on being heated. The same bending can be seen if a strip of sticky tape is fastened to a strip of aluminium foil. The foil expands when it is heated, but the tape prevents the stretching of that side of the foil, so the 'bimaterial' bends, with the sticky tape on the concave side.
Answer:
Disadvantage of clinical thermometer.. Are :
1. We cannot use clinical thermometer for measuring the temperature of any object more than 42 degree celcius...
2. It may break when kept in the sun or near a flame
Hope it helps..