Page 3
User Supplement
Target Orbiting Thermometer
3 Principle of Operation
Fig. 1 shows the field of view for a standard System 4 Thermometer. The axis
of the field of view is fixed at the centre of the thermometer lens and is at
right angles to the front face of the thermometer.
Fig. 2 shows the field of view for a Thermometer fitted with the Target
Orbiting (TO) option. The target size at any given distance is identical to
that of the corresponding standard Thermometer. However, the field of view
rotates about a cone of half-angle 2°, centred on the opto-mechanical axis
of the Thermometer. The frequency of rotation is 3Hz. The Target Orbiting
Thermometers achieve a peak temperature output in excess of 99.5% of
value (in degrees) for any target surface whose width is greater than, or
equal to, 1.2 times the target spot diameter (1.5 times for 200:1 field of view
thermometers).
The Target Orbiting option is designed for use on moving or intermittent
targets. In a standard System 4 Thermometer, the eyepiece graticule defines
the target spot. In a Target Orbiting Thermometer, the graticule defines the
orbit of the centre of the target spot (refer to Fig. 3 overleaf). It can be
seen from Fig. 3 that, for a narrow object (e.g. wire), it is possible that the
target may not be covered by the graticule for considerable periods, due
to lateral movement of the product with respect to the thermometer. In a
Target Orbiting Thermometer, this is not a problem as the Thermometer can
be sighted so that the graticule covers the limits of lateral movement. This
means that an accurate, valid temperature reading will be obtained by the
thermometer at least three times per second. When used in conjunction with
the ‘Peak Picking’ function of either the Landmark Graphic, Landmark Classic
or Landmark Basic processor, the true temperature of the target can be
ascertained.
Non target orbiting
Thermometer
Target orbiting
Thermometer
Limits of lateral
movement
Limits of lateral
movement
P
ro
d
u
ct
d
ir
ec
ti
on
o
f
tr
a
ve
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Fig. 3 Comparison of views through the eyepiece (Standard v Target Orbiting)
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