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Technical Library |
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Temperature Sensors |
Temperature Sensors come in many different styles and configurations. They are
available in analog or digital, wireless or hard-wired. Big differences exist between
temperature sensor or temperature measurement device types. Using one perspective,
they can be simply classified into two groups, contact and non-contact.
All sensor have errors in their readings - all the time. One key
secret to high quality measurement results is to have confidence in the error estimates.
Neglecting to make a careful error analysis can result in error much larger than the assumed values.
It is worth noting that all competent error analyses start with the uncertainties assigned
to the traceable calibration of the sensor itself. Without traceable calibration, one is forced
to make assumptions. A great many temperature measurement problems are solved through a good
understanding of the heat flow involved in a specific measurement situation.
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Without traceable measurements, the numerical values of results will always be questionable
and hardly worth the effort, and cost. It most often pays to get started on the right path
to technically sound measurements by beginning with some understanding of the options involved
in selecting a temperature measurement device and then in obtaining one that meets the expected
conditions and standards, is calibrated and that the calibration is traceable to either a
fundamental standard (e.g. the triple point of water) or a national standard.
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Contact Sensors - Contact sensors measure their own temperature. One infers the temperature of the
object to which the sensor is in contact by assuming or knowing that the two are in thermal
equilibrium, that is, there is no heat flow between them.
All sensor have errors in their readings - all the time. One key
secret to high quality measurement results is to have confidence in the error estimates.
Neglecting to make a careful error analysis can result in error much larger than the assumed values.
Non Contact Sensors - Most commercial and scientific noncontact temperature sensors
measure the thermal radiant power of the Infrared or Optical radiation that they receive
from a known or calculated area on its surface, or a known or calculated volume within it
(in those cases where the obect is semitransparent within the measuring wavelength passbad of the sensor).
One then infers the temperature of an object from which the radiant power is assumed to be
emitted (some may be reflected rather than emitted). Sometimes the inference requires a correction
for the spectral emissivity (the two words, spectral & emissivity, are used together in
correcting IR Thermometer readings -the "emissivity", unspecified, is a big trap which even some
of the suppliers of devices and calibration equipment fall into unwittingly for a variety of
reason about which one can only speculate ) of the object being measured.
Knowing how and when to apply a spectral emissivity correction is part of the inference,
too, and can introduce significant errors if not done correctly.
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Temperature Sensor Information Links
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Temperature Sensor Manufacturer Links
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