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R4 Thermometer
4.2 Aiming the Thermometer at the Target
When the thermometer has been correctly installed in the desired location,
it must then be aimed at the target area using the in-built Laser Alignment
facility.
The laser is triggered into operation by the use of a push button switch
which applies a transient signal (changing from a positive voltage to 0V) to
the signal 4 terminal. Once activated, the laser remains on, irrespective of
the switch position, for a period of between 50 and 60 seconds after which
time it switches off automatically. The laser beam has been aligned during
manufacture to be coincident with the optical centre of the thermometer's
infrared viewing axis.
Remember that the measurement target is much larger than the laser spot,
the size being defined as in Section 3.2.
There are two different possibilities for positioning the trigger switch:
•
Operation from LMG signal processor rear panel.
•
Operation from an auxiliary push button switch mounted near to the
thermometer jacket when the signal processor is distant from the
thermometer location.
Further information detailing the connections required, for both methods of
positioning the trigger switch, can be found in the Thermometer Installation
Guide.
4.3 Electrical Connections
The electrical connections for the thermometer power supply and temperature
outputs are made via the 8-way socket on the rear of the thermometer.
Fig. 6 Location of 8-way electrical connection socket
NOTE
Cable lengths - The maximum overall resistance of the cable used to
connect the thermometer to the processor is 20 ohms. The commonly
used cable is 7 x 0.2mm core, which is rated at 92 ohms per km thus
allowing a maximum cable length of 217 metres (i.e. 20/92 x 1000
m). This is the maximum total cable length. Therefore we recommend
a maximum cable length of 200 metres, including any junction boxes:
e.g. Thermometer > 150m cable > Junction box > 50m cable > Processor
Page 6
User Guide
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