Technical Manual
|
Dräger Polytron
®
8000 Series
63
Instrument settings
The relay labels (NO, COM, NC) represent the default state (normally energized) of
all relays while the instrument is powered
12.9.1 SPDT
Relays
Single Pole Double Throw (SPDT) relays switch the terminal (COM = Common)
between 2 contacts (NO = Normally Open and NC = Normally Closed).
If the relay coil is energized, the terminal connects with the Normally Open contact.
Fig. 16
Energized and de-energized status of a SPDT relay
Relay configurations determine which status the relay has during normal operation.
There are 2 relay configurations: Normally Energized and Energized on alarm.
Relay configuration: Normally Energized
During normal operation the relay is energized and the Normally Open contact
connects with the Common terminal.
If an alarm is triggered, the relay is de-energized and the Common terminal
connects with the Normally Closed contact.
Power loss to the transmitter also de-energizes the relay, connecting the terminal to
Normally Closed.
Relay configuration:
Energized on alarm
During normal operation the relay is de-energized and the terminal connects with
the Normally Closed contact.
If an alarm is triggered, the relay is energized and the terminal connects with the
Normally Open contact.
Power loss to the transmitter has no influence on the terminal position.
12.9.2
Relay contacts and relay configuration
The following tables show the status of a connected alarm indicator and whether it
indicates faults such as power loss to the transmitter.
The relay’s behavior depends on the alarm configuration and the relay contact to
which the alarm indicator is connected.
3
6572
NC
NO
COM
coil -
coil +
NC
NO
COM
coil -
coil +
Energized
De-energized
