28 900 Series V5.0: Installation Guide, April 1999
The yellow LED illuminates when a fault condition (open or short circuit) is detected.
3.4.3.4. Switch Monitor Plus - II953D
Function: The Series 950 DIN-rail Switch Monitor Plus monitors the state of one or more
single pole, volt free contacts connected on a single pair of cables, and reports the status
to analogue control equipment. The Switch Monitor Plus has an output for resetting a
remote detector and a selectable alarm delay, making it suitable for monitoring flow
switches.
Features: The Switch Monitor Plus provides four input states to the control equipment:
'Normal', 'Fault', 'Pre-alarm' and 'Alarm'. It has a red LED to indicate an alarm and a
yellow LED to indicate a fault condition. Select the 30 second delay by using the eighth
bit of the DIL switch.
Electrical considerations: The Series 950 DIN-rail Switch Monitor Plus is loop powered
and operates at 14-28 VDC. The Switch Monitor Plus accepts a maximum line resistance
of 50 kOhm. The end-of-line resistor required is 20 kOhm. The opto-coupled reset takes
the form of a current limited transistor output.
Mechanical construction: Two LEDs (one red and one yellow) are visible through the
top cover of the enclosure.
The red LED is switched by the control panel and illuminates when an alarm condition is
detected. The yellow LED illuminates when a fault condition (open or short circuit) is
detected.
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