bending of the strip, which allows quantifying the temperature. The bimetallic
thermometers may be incorporated in thermostats wherein the bending metallic
strip activates a mechanism for environmental temperature control. The classical
mercury thermometers and bimetal thermometers have been replaced by
transducers with electrical measurement principles.
The electronic thermometers are the most used devices for temperature
measurements in environmental applications (Fig. A1.6).
The electronic transducers of temperature measurement must be of dimensions
and geometrical forms compatible with any type of utilization allowing for digital
or analogue outputs, which may be saved or processed in an expedite way. Four
main types of electronic sensors are thermocouples, thermistors, diodes, and
platinum resistance thermometers (PRT).
Thermocouples are common sensors based the Seeback effect that which if two
metals are connected to establish an electric circuit and if the two junctions are at
two distinct temperature, an electromotive force (emf) will be generated (DV) which
is proportional to temperature difference (DT) so that (e.g, Oke 1992):
DV ¼ a 1 DT þ a 2 DT
2
ðA1:17Þ
In real conditions, under the temperature ranges prevailing in the surface layer,
the second term on the right side can be cancelled. The sensitivity of thermocouples,
evaluated through the constant a 1 , is dependent on the metals used. For the
thermocouples of combination of copper and constantan (Fig. A1.7), which can be
used at temperatures ranging between −200 and 350 °C, sensitivity ranges between
40 and 60 lV °C
−1 .
For the thermocouples using platinum and rhodium, usable at temperatures
ranging between 0 and 1600 °C the sensitivity is lower of around 10 lV °C
−1 .
Thermocouples of iron and constantan can be used at temperatures ranging between
−40 750 °C with a sensitivity of 55 lV °C
−1 .
Fig. A1.6 Example of an
electronic thermometer
Annex A1: Instrumentation in Environmental Physics
319
thermometers may be incorporated in thermostats wherein the bending metallic
strip activates a mechanism for environmental temperature control. The classical
mercury thermometers and bimetal thermometers have been replaced by
transducers with electrical measurement principles.
The electronic thermometers are the most used devices for temperature
measurements in environmental applications (Fig. A1.6).
The electronic transducers of temperature measurement must be of dimensions
and geometrical forms compatible with any type of utilization allowing for digital
or analogue outputs, which may be saved or processed in an expedite way. Four
main types of electronic sensors are thermocouples, thermistors, diodes, and
platinum resistance thermometers (PRT).
Thermocouples are common sensors based the Seeback effect that which if two
metals are connected to establish an electric circuit and if the two junctions are at
two distinct temperature, an electromotive force (emf) will be generated (DV) which
is proportional to temperature difference (DT) so that (e.g, Oke 1992):
DV ¼ a 1 DT þ a 2 DT
2
ðA1:17Þ
In real conditions, under the temperature ranges prevailing in the surface layer,
the second term on the right side can be cancelled. The sensitivity of thermocouples,
evaluated through the constant a 1 , is dependent on the metals used. For the
thermocouples of combination of copper and constantan (Fig. A1.7), which can be
used at temperatures ranging between −200 and 350 °C, sensitivity ranges between
40 and 60 lV °C
−1 .
For the thermocouples using platinum and rhodium, usable at temperatures
ranging between 0 and 1600 °C the sensitivity is lower of around 10 lV °C
−1 .
Thermocouples of iron and constantan can be used at temperatures ranging between
−40 750 °C with a sensitivity of 55 lV °C
−1 .
Fig. A1.6 Example of an
electronic thermometer
Annex A1: Instrumentation in Environmental Physics
319