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Figure 4b - When a short occurs at a point along the detectors length an initiating device circuit detects the
short and then automatically switches to a thermocouple measurement mode. The shorted portion of the de-
tector forms a thermocouple junction which can be measured. The thermocouple measurement represents the
current temperature of the shorted portion of detector. If the short is below the pre-set alarm threshold for the
detector, in this example 280°F (138°C), a short fault is reported instead of an alarm condition.
Figure -4b
Figure 5 - If the short temperature is measured to be above the pre-set 280°F (138°C) alarm threshold, as in
this example, an alarm condition is produced immediately.
COLD
TEMP
Monitor
Circuit
End Line
Resistor
Heat Sensitive
Insulation
Short
Y
82f-27C
HEAT
TEMP
Monitor
Circuit
End Line
Resistor
Heat Sensitive
Insulation
Alarm
R
282f-139C
Figure -5
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