Dräger REGARD 3900 Serie Instrucciones De Uso página 60

Installation & commissioning
Diode circuit
Power AC LED
If the control unit is supplied with both AC and DC power supply, it is best to
connect the 24 V output of the energy supply unit to the AC on terminal on the Sk2
of the display PCB. Once a connection has been established, the power AC-LED
lights up if the control unit is being supplied via the (primary) AC voltage supply. If
the control unit is being supplied via the (supporting) DC voltage supply the LED is
off.
A diode is required to protect against power from the backup supply that can
incorrectly indicate a functioning AC voltage supply (see diode circuit).
5.6 Installation of the control modules
Output modules are not part of the ATEX EC type examination of the REGARD
3900. If an output module is installed, the control unit must not be used to monitor
measures against explosion hazards.
The control unit can contain up to six control modules.
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REGARD 3900