D:s Ratio: D / S = 90; Optical Diagram; Field-Of-View - Fluke Ti30 User Manual

D:S ratio: D / S = 90

The number "90" means that at a distance D equal to 1 meter the unit will measure a circle
of diameter S equal to 1.1cm (1 meter divided by 90); at distance D equal to 2 meters it will
measure a circle with diameter S equal to 2.2cm and so on in a linear progression.

Optical Diagram

The optical diagram shows the graphical representation of the optical ratio. The optical path
of the infrared radiation is a cone that has its vertex at 61cm (24") away from the front of
the unit, and progresses at the same ratio towards infinity. The circle diameter can be
calculated by dividing the distance by 90 at any point in the centerline of the cone. Below it
is presented the diameters S for three different distances: 61cm (minimum distance), 2m and
5m. There is no maximum distance. Although, in practical terms, accurately measuring
temperatures of targets a great distance away requires very large objects.
Figure 56. Illustration of Distance to Target / Spot Ratio
The explanation of optical resolution is key for the understanding of the next concept, vital
for accurate temperature measurement in quantitative inspections.

Field-of-View

Make sure that the target is larger than the spot size that the unit is measuring. The
smaller the target, the closer you should be to it.
Jan 31st, 2005 - 63 -