Section 150-232-100
Revision 01
Page 17
The Lock-In thresholds provide a mechanism to prevent repetitive switchover/reverts in the event of recurring
intermittent fault conditions. These thresholds are set by the G, H & I options in the Protection Switch Configuration
menu shown in Figure 16. After G switchovers in H minutes, the switchover to the protect circuit remains (does not
revert) for I hours. The ranges and (default) settings for these three parameters are:
G:
1 to 9 minutes (4)
H:
1 to 99 minutes (10)
I:
1 to 99 hours (24)
6.05 A minor alarm HBER (high BER) is generated in either the Primary or Protect HLU whenever that HLU
determines that its current BER exceeds the user-selected threshold. Note that an HBER or any other alarm
condition in the Protect circuit will inhibit a switchover. When such a condition exists the message SWITCHOVER
LOCKED OUT appears in the PROTECTION SYSTEM STATUS field of the Protection System Configuration Menu
shown in Figure 16. A minor alarm PROR is displayed on the Protect HLU whenever the Protect HLU does not
receive positive confirmation that the Protect HRU has switched or reverted when requested. These events are
accumulated in the Switchover Event History shown in Figure 18.
6.06 Error free transmission is hindered for a maximum of 100 milliseconds during either a switchover or revert
event. This is a result of the need to switch the T1 Receive output from the off-line to the on-line circuit as shown in
Figure 2. The transmit (input) circuits can also be affected during switchover but to a lesser degree. The single T1
input is connected to both T1 inputs of the two units (HLU & HRU) at each end of the circuit. At the HLU the input
100 ohm input impedance switches with the on-line unit. This prevents any service errors when the defective HLU is
replaced. However, BPV and LOS conditions can occur at the HLU end during switchover. At the HRU end the two
T1 inputs are hard wire connected by a 6 db power splitter which does not change during a switchover. However
removal of the defective HRU causes the input impedance to increase which could cause some BPVs in the on-line
circuit.
6.07 AHLD is the AUTO HOLD mode. It operates exactly like the APRO mode except it is non-reverting. If
switchover occurs, the Protect circuit is locked on-line until the operator forces it out by changing to another protect
mode. The Protect HLU displays the AHLD message when in this mode.
6.08 MPRO is the MANUAL PROTECT mode. It forces the system to the Protect circuit where it remains until the
mode is changed. The Protect HLU displays the MPRO message when in this mode.
6.09 MDIS is the MANUAL DISABLE mode. It overrides and resets any automatic or manually activated Protect
mode and forces the system to the Primary circuit where it remains until the mode is changed. The Protect HLU
displays the MDIS message when in this mode.
6.10 For Protection Switching applications, ESAL (Errored Seconds Alarm) should be disabled.
6.11 It is recommended that the same BER threshold and BER measurement interval settings be used on both the
Primary and Protect line units.
6.12 It is recommended to have a Protect line unit installed while operating in MPRO (Manual Protect) mode.
Change the Protection Mode setting to another value before removing the card.
