Thermometer is a device used to measure temperature.
The various kinds of themometer available are
Thermistors
A thermistor is a type of resistor used to measure temperature
changes, relying on the change in its resistance with changing temperature.
Thermistor is a portmanteau word from the words thermal and resistor.
Thermocouples
In electronics, thermocouples are a widely used type of
temperature sensor. They are cheap, interchangeable, have standard connectors
and can measure a wide range of temperatures. The main limitation is accuracy;
system errors of less than 1 °C can be difficult to achieve. A thermopile
is a group of thermocouples connected in series.
Mercury-in-glass thremometer
mercury-in-glass thermometer is a thermometer consisting
of mercury in a glass tube. Calibrated marks on the tube allow the temperature
to be read by the length of the mercury within the tube, which varies
according to the temperature. To increase the sensitivity, there is usually
a bulb of mercury at the end of the thermometer which contains most of
the mercury; expansion and contraction of this volume of mercury is then
amplified in the much narrower bore of the tube. The thermometer was used
by the originators of the Fahrenheit and Celsius temperature scales.
bi-metal thermometer
A bi-metallic strip is used to convert a temperature change
into mechanical displacement. The strip consists of two layers, usually
iron and copper. The two layers are joined together to form the strip.
Owing to the difference in the constants of expansion of the two materials,
a flat strip will bend one way (toward the iron part) if heated, and in
the opposite direction if cooled below its normal temperature. In some
applications the bi-metal strip is used in the flat form. In others, it
is wrapped into a coil, which gives greater sensitivity in a compact space.
Silicon bandgap temperature sensor
The silicon bandgap temperature sensor is an extremely
common form of temperature sensor (thermometer) used in electronic equipment.
Its main advantage is that it can be included in a silicon integrated
circuit at very low cost. The principle of the sensor is that the forward
voltage of a silicon diode is temperature-dependent, according to the
following equation:
infrared thermometer
Infrared pyrometers allow users to measure temperature
in applications where conventional sensors cannot be employed. Specifically,
in cases dealing with moving objects ( i.e., rollers, moving machinery,
or a conveyor belt), or where non-contact measurements are required because
of contamination or hazardous reasons (such as high voltage), where distances
are too great, or where the temperatures to be measured are too high for
thermocouples or other contact sensors.
galileo thermometers
Galileo's thermometer is made of a sealed glass cylinder
containing a clear liquid. Suspended in the liquid are a number of weights.
The picture shows those weights as themselves sealed glass containers
with coloured liquid for an attractive effect. As the liquid changes temperature
it changes density and the suspended weights rise and fall to stay at
the position where their density is equal to that of the surrounding liquid.
If the weights differ by a very small amount and ordered such that the
least dense is at the top and most dense at the bottom they can form a
temperature scale. The temperature in the case of the picture is read
from the engraved metal disc on each weight. The lowest weight of the
top set of weights is the temperature, in this case accurate to two degrees.
This is done by manufacturing the weights to within 1/1000 to 1/3000th
of a gram.
Various other kind of thermometers
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