900 Series V5.1: Installation Guide, February 2000
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The Series 950 DIN-rail input/output unit provides a voltage-free, single pole, change-
over relay output, a single, monitored switch input, and an unmonitored, non-polarised
opto-coupled input. The unit supervises one or more normally open switches connected
to a single pair of cables.
The Series 950 DIN-rail input/output unit is loop powered.
Three LEDs, two reds and one yellow, are visible through the top cover of the enclosure.
One red LED illuminates when the relay is set. The second red LED illuminates when the
switch input is closed.
The yellow LED illuminates when a fault condition (open or short circuit) is detected.
If you do not need these LEDs, or the extra loop current to illuminate them is unavailable,
they can be disabled by using the eighth segment of the DIL switch.
3.4.3.3. Switch Monitor - II952D
The Series 950 DIN-rail Switch Monitor 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.
Figure 24: Wiring connections (Switch Monitor – DIN mount)
The Switch Monitor provides four input states to the control equipment: 'Normal', 'Fault',
'Pre-alarm' and 'Alarm'. These are derived from the switched resistive values shown in
Figure 24. The switch monitor has a red LED to indicate an alarm and a yellow LED to
indicate a fault condition.
The Series 950 DIN-rail Switch Monitor is loop powered and operates at 14-28 VDC. The
switch monitor is designed to accept a maximum line resistance of 50 Ohm. The end-of-
line resistor required is 20 kOhm.
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 can be illuminated when an alarm
condition is detected.
Â
Á
Switch closed
Fault
Series 950 loop
Note: Line 1 and Line 2 are polarity insensitive but it is recommended to keep L1 negative
for consistency.
À
Normaly open fault contacts
Â
Pre-alarm contacts
Á
Fire contacts
SW
SW
