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2.7  Optical Charts 
The  following  optical  charts  show  the  diameter  of  the  measuring  spot  in  dependence  on  the  distance 
between measuring object and sensing head. The spot size refers to 90 % of the radiation energy. 
The distance is always measured from the front edge of the sensing head. 
 
As an  alternative to the optical diagrams, the spot size calculator can also be used on the 
Optris website or via the Optris calculator app. The app can be downloaded for free from the 
Google Play store (see QR code). 
 
 
D = Distance from front of the sensing 
head to the object 
 
S = Spot size 
 
The  size  of  the  measuring  object  and  the  optical  resolution  of  the  infrared  thermometer 
determine the maximum distance between sensing head and measuring object. 
In  order  to  prevent  measuring  errors  the  object  should  fill  out  the  field  of  view  of  the  optics 
completely. 
Consequently, the spot should at all times have at least the same size like the object or should 
be smaller than that. 
 
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