Temperature Sensor Buying AdviceTemperature sensors are specially designed
devices to detect the temperature or humidity of certain
objects or area. The intensity of an object's discharged
Infrared radiation energy increases or decreases in proportion
to its temperature. It is the emitted energy, measured as the
target's emissivity, which indicates an object's temperature.
Emissivity is a term that is used to specify the quantity of
the energy-emitting characteristics of different materials and
surfaces. IR temperature sensors have adjustable emissivity
settings, which allow accurate temperature measurements of
several surface types. |
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The radiated energy comes from an object and reaches the IR
sensor through its optical system, which focuses the energy onto one
or more photosensitive detectors. The detector then converts the IR
energy into an electrical signal, which is in turn converted into a
temperature value based on the sensor's calibration equation and the
target's emissivity amount. This temperature value can be displayed
on the sensor, or, in the case of the smart sensor, converted to a
digital output and displayed on a computer screen.
There are
differences existed between different temperature sensors or
temperature measurement device types. From one point of view, they
can be simply classified into two groups, contact and non-contact.
On the current market, there are vendors of each temperature sensor
type, some vendors sell more than one type and some sell nearly all
types, but not always all brands. There are differences between
brands and the differences are most evident among those device types
for which there are few if any recognized standards. You can
probably start your hunting journey either for a specific
temperature sensor type or go to the vendor page index and you can
access the vendors of specific types from there.
Both
contact and non-contact sensors require some assumptions and
inferences in use to measure temperature. Remember the truism that
all sensors have errors in their readings. 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.
Contact
temperature sensor 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.
Most commercial and scientific non-contact 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.
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 (NB: 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. See our Trip
down the E-missivity Trail to help you understand that aspect a
little better.
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