DDB signal (Opto-input) DDB signal
Input L3 (DDB: 34) Aided 1 Scheme Rx (DDB: 493)
Input L4 (DDB: 35) Aided 1 COS/LGS (DDB: 492)
The Aided 1 Scheme RX signal corresponds to a 'channel-receive' signal for scheme 1. The Aided 1 COS/LGS signal
corresponds to a 'channel out of service' or 'loss of guard' signal ('Loss of guard' is the inverse signal to 'guard
received').
As well as the default mapping, it is possible to map the signals to other inputs if required.
The window during which the unblocking logic is enabled starts 10ms after the guard signal is lost and continues
for 150ms. The 10ms delay gives time for the signalling equipment to change frequency.
Note:
If the Z1 Ext Scheme setting is set to operate for channel failure, the Zone 1 extension logic will be invoked if a channel failure
is detected.
This scheme type also provides Loss of Guard logic as described below.
System condition
Permissive
channel received
Loss of guard
Permissive
trip allowed
Alarm
generated
Healthy Line No No No No
Internal Line Fault Yes Yes Yes No
Unblock No Yes Yes, during a 150 ms window Yes, delayed on pickup by 150 ms
Signalling Anomaly Yes No No Yes, delayed on pickup by 150 ms
P543i/P545i Chapter 8 - Carrier Aided Schemes
P54x1i-TM-EN-1 221
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