SM0486
determine the resistance of the thermometer by multiplying the ratio by 25.54900
(thermometer resistance at 0). This product is nearly 30.60030. When you locate
the resistance value 30.60030 on the section of the resistance-temperature
conversion chart shown in table 5, A, you see that the temperature measured by the
resistance thermometer is 50C.
5.
THERMOMETER CALIBRATION
a. One of the requirements is that you learn more about the calibration of
thermometers.
You must increase your ability to apply thermal measurement
principles in the calibration of thermometers.
When we use the term "thermal
measurement principles," we are thinking of the physical laws and concepts of heat
and temperature which we have discussed.
These theories and concepts form the
basis for the thermal principles applied when you calibrate thermometers.
The
physical laws we have in mind are as follows:
Heat is the total kinetic energy of moving molecules.
Heat is transferred from one body to another by means of conduction,
convection, radiation-absorption, or some combination of these processes.
The intensity of heat in a body is called its temperature.
The intensity of heat in a body is indicated on scales which relate the
intensity of the heat in that body to the intensity of heat necessary to raise
water to its boiling point or lower water to its freezing point.
Electrical energy can be transformed into heat (kinetic) energy.
The absence of heat is cold.
b. The thermometer scales in figure 3 show that the freezing points and the
boiling points of water are reference points for thermometers regardless of the
scale used.
From table 4 it should be obvious that you may be required to
calibrate thermometers other than the mercury-in-glass type.
Regardless of the
type, the measurement principle and the laws of physics which support this
principle remain the same.
For example, when you calibrate a thermometer, what
does the measurement process include?
Regardless of the type of thermometer
calibrated, you merely insert the thermometer being calibrated into a measurement
chamber and compare the thermometer reading with the reading indicated on the
measurement chamber readout device. The answer to the question you are thinking is
yes; the measurement chamber readout device has to be calibrated with the
resistance thermometer before it is used.
c. Your laboratory uses a temperature calibrator to check the accuracy of
other temperature devices.
The rough sketch in figure 10 represents one of the
calibrators which you may use.
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