Schweitzer Engineering Laboratories SEL-311L, Instruction Manual, Page: 433 / 734

Date Code 20010625 Line Current Differential Communications 10-7
and Serial Port Communications and Commands
SEL-311L Instruction Manual
assert when any of those three parameters exceed a user-defined threshold. CHXAL and
CHYAL do not effect protection, and are not an indication that 87L protection is not available.
Relay Word bit 87LPE deasserts when 87L protection is not available due to a channel problem.
When either CHXAL or CHYAL assert, or when 87LPE deasserts, front-panel LED 87CH FAIL
illuminates. Several settings control the alarm thresholds for the channel monitors, as described
below. Access those settings described below with the
SET X and SET Y commands. There are
no settings associated with 87LPE.
Setting EADDCX and EADDCY (Address Checking)
Set EADDCX = Y (EADDCY = Y for Channel Y) to enable receive message address checking.
Transmitted messages contain an address field. When EADDCX = Y, the transmitting relay
places the address defined by setting TA_X (or setting TA_Y for Channel Y) in the transmitted
message. The receiving relay checks to ensure that the address contained in the message
matches the local RA_X setting (or RA_Y setting for Channel Y). If the received address does
not match the receive address setting, the relay discards the message as if it were corrupted.
Address checking serves two purposes. The first purpose is to avoid misoperations due to
inadvertent loopbacks in the network or multiplexer equipment. An inadvertent loopback might
also occur if light from a fiber-optic transmitter reflects off a surface and returns to a receiver.
To effectively detect inadvertent loopbacks, set RA_X different than TA_X. The second purpose
is to avoid misoperations due to misrouted communications links. To effectively detect
misrouted communications links, set RA_X and TA_X uniquely for each SEL-311L Relay
connected to the network. For direct-fiber connections, set RA_X and TA_X uniquely for each
SEL-311L Relay with a fiber pair in a bundle, or for each SEL-311L Relay with a fiber pair
routed through a patch panel.
Settings RBADXP, RBADYP, AVAXP, and AVAYP (Availability Monitors)
Settings RBADXP and AVAXP (RBADYP and AVAYP for Channel Y) together detect channel
loss and degradation. When no acceptable packets have been received for longer than setting
RBADXP (in seconds), Relay Word bit RBADX asserts. This asserts Relay Word bit CHXAL
and illuminates front-panel LED 87CH FAIL.
When the number of packets corrupted or lost from the previous 10,000 packets exceeds setting
AVAXP, Relay Word bit AVAX asserts. This asserts Relay Word bit CHXAL, and illuminates
front-panel LED 87CH FAIL. Use Relay Word bit CHXAL to assert an alarm, turn on a display
point, etc.
Together, AVAXP and RBADXP detect short-term interruptions and long-term degradation of
the communications circuit. After the problem is repaired, Relay Word bit AVAX resets itself in
less than 15 seconds, and RBADX resets itself instantly. Settings AVAYP and RBADYP and
Relay Word bits AVAY and RBADY operate the same for Channel Y.
Settings DBADXP and DBADYP (Channel Delay Monitors)
Setting DBADXP (DBADYP for Channel Y) detects longer than expected channel delays. Such
increased delays might be caused by channel re-routes on a switched network. When the
estimated one-way channel delay exceeds setting DBADXP (in milliseconds), Relay Word bit