13.5.2.3
Unblocking scheme
In unblocking scheme, the lower dependability in permissive scheme is overcome by
using the loss of guard signal from the communication equipment to locally create a
receive signal. It is common or suitable to use the function when older, less reliable,
power line carrier (PLC) communication is used.
The unblocking function uses a guard signal CR_GUARD, which must always be
present, even when no CR signal is received. The absence of the CR_GUARD signal
for a time longer than the setting
tSecurity
time is used as a CR signal, see figure
.
This also enables a permissive scheme to operate when the line fault blocks the signal
transmission.
The received signal created by the unblocking function is reset 150 ms after the
security timer has elapsed. When that occurs an output signal LCG is activated for
signaling purpose. The unblocking function is reset 200 ms after that the guard signal
is present again.
CR_GUARD
0-tSecurity
0
150 ms
CR
CRL
LCG
AND
OR
AND
en05000746_ansi.vsd
0
0
200 ms
NOT
OR
ANSI05000746 V1 EN
Figure 403:
Guard signal logic with unblocking scheme
The unblocking function can be set in three operation modes (setting
Unblock
):
Disabled:
The unblocking function is out of operation
No restart:
Communication failure shorter than
tSecurity will be ignored
If CR_GUARD disappears, a CRL signal will be transferred to the trip logic
There will not be any information in case of communication failure (LCG)
Restart
Communication failure shorter than
tSecurity will be ignored
It sends a defined (150 ms) CRL after the disappearance of the CR_GUARD signal
The function will activate LCG output in case of communication failure
If the communication failure comes and goes (<200 ms) there will not be recurrent
signaling
1MRK505222-UUS C
Section 13
Scheme communication
815
Technical reference manual
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