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Operation
4.5.3 Ambient Temperature Compensation
The sensor is capable of improving the accuracy of target temperature measurements by taking into
account the ambient or background temperature. This feature is useful when the target emissivity is
below 1.0 and the background temperature is significantly hotter than the target temperature. For
instance, the higher temperature of a furnace wall could lead to hotter temperatures being measured
especially for low emissivity targets.
Ambient background temperature compensation allows for the impact of reflected radiation in
accordance with the reflective behavior of the target. Due to the surface structure of the target, some
amount of ambient radiation will be reflected and therefore, added to the thermal radiation that is
collected by the sensor. The ambient background temperature compensation adjusts the final result by
subtracting the amount of ambient radiation measured from the sum of thermal radiation the sensor is
exposed to.
The ambient background temperature compensation should always be activated in case
of low emissivity targets measured in hot environments or when heat sources are near
the target!
Three possibilities for ambient background temperature compensation are available:
The internal sensing head temperature is utilized for compensation assuming that the ambient
background temperature is more or less represented by the internal sensing head temperature.
This is the default setting.
If the background ambient temperature is known and constant, the user may give the known
ambient temperature as a constant temperature value.
Ambient background temperature compensation from a second temperature sensor (infrared
or contact temperature sensor) ensures extremely accurate results. For example, a second IR
sensor, configured to provide a 0 to 5 volt output scaled for the same temperature range as the
target can be connected to input FTC2 to provide real-time ambient background compensation.
Figure 23: Principle of Ambient Background Temperature Compensation
30
Sensor 2
targeted
to ambient
0 – 5 VDC
analog output at
FTC2 input
Sensor 1
targeted
to object
Thermal radiation
of ambient
Thermal radiation
of target
Rev. B2 Feb 2017
Furnace wall
Target object
XR
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