Adjusting The Emissivity; Use Of The Pilot Light - LumaSense Technologies IGA 740 Betriebsanleitung

IGA 740

7.2 Adjusting the emissivity

The emissivity is the relationship between infrared energy radiated from an object and the radiation energy of
a perfect emitter (black emitter) at the same temperature and the same spectral range.
The emissivity is material-dependent and of a considerable size in order to be able to determine the temper-
ature of an object accurately without contact. The emissivity of the object being measured must therefore be
known and be adjusted at the pyrometer.
Typical emissivities for various materials are available on our homepage at www.lumasenseinc.com or in rele-
vant literature.
The instrument is calibrated at black body radiation ( = 1,00). Real objects have an emissivity less than
1.00. This difference can be adjusted with changing the emissivity value from the pyrometer.
How to find out correct emissivity:
1. First measure the real temperature of measuring object with a contact thermometer e.g. thermocouple or
resistance probes. The "black" temperature (spectral temperature) measured with a pyrometer adjusted
to emissivity = 1.0 usually gives a measuring value differing to real temperature because of the real
emissivity of < 1.0. The value given by the instrument usually will be less than the real temperature. The
emission ratio of most materials depends on temperature as well as wave length being measured.
2. You can get a correlation of the temperature scales, if you adjust the pyrometer at the exact temperature
with the help of the emissivity value.
After adjusting the emissivity factor through a correlation measurement you can now measure
temperatures for the calibrated temperature range at an accuracy mentioned in the technical data.
IMPORTANT:
Please pay attention if you take over table values of emissivity to give the value of emissivity factor at a
certain wave length. Adjusting emissivity following table values is not as exactly as adjusting following
a comparing measurement.
Changing emissivity
With the help of a suitable screw driver and without any violence you can adjust emissivity at the rear side of
the pyrometer stepless between 0.1 and 1.

7.3 Use of the pilot light

With the help of the pilot light the measurement point can easily determined.
For devices with a spectral range of 0.85 . . . 1.05 m, the pilot light has to switched off during the measurement,
as this may falsify the measurement result.
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