Dräger REGARD 3900 Series Instructions For Use Manual page 10

Components
4 Components
4.1 General instructions
The control unit has a display PCB and up to six control modules. The control
modules are a combination of input modules, relay modules and output modules,
which can be flexibly arranged as far as the control unit allows this. Internally, all
control modules and the display PCB are connected using a ribbon cable.
The control unit can be supplied from an AC or DC power source or both.
Irrespective of the power supply to the control unit, the internal control modules
receive a 24 V DC supply.
The following internal LEDs are in operation during use:
– There is a green LED on each control module to indicate that the internal DC
voltage is being applied.
– Two red LEDs on the right side of the display PCB and on each control module
flicker during normal operation.
– In addition to each relay on an input module or relay module, a red LED lights up
when the relay is activated.
4.2 Display PCB
The display PCB is inside the control unit and houses the display screen and the
LEDs on the front panel. The display screen and the LEDs provide information and
warning messages relating to the statuses measured at the remote sensor
transmitters. The inhibit switch and the contrast setting are also found on the
display PCB.
4.2.1 Inhibit switch
The inhibit switch is used during maintenance or repair work on the control unit to
maintain the current status of the control unit relay; this prevents the gas warning
messages from being activated. The inhibit switch operates as follows:
Position
0
1
WARNING
If the inhibit switch is moved to position 1, the control unit relays remain in their
current status and the gas value warning messages cannot be activated.
► Always bring the switch back to position 0 after maintenance or repair work.
Effect
All relays are operating normally
Relays whose feature is "Alarm locked" are activated (associated
remote warning devices are also activated).
All other relays remain in their current state.
The inhibit LED lights up.
The active LEDs flash and the acoustic alarm sounder beeps
every 30 seconds.
The signals of the output modules are frozen in their current
state.
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REGARD 3900