GE L60, Instruction Manual, Page: 132 / 498

5-40 L60 Line Phase Comparison Relay GE Multilin
5.2 PRODUCT SETUP 5 SETTINGS
5
b) CRC ALARM CH1(2)
PATH: SETTINGS PRODUCT SETUP DIRECT I/O CRC ALARM CH1(2)
The L60 checks integrity of the incoming direct input/output messages using a 32-bit CRC. The CRC Alarm function is
available for monitoring the communication medium noise by tracking the rate of messages failing the CRC check. The
monitoring function counts all incoming messages, including messages that failed the CRC check. A separate counter adds
up messages that failed the CRC check. When the failed CRC counter reaches the user-defined level specified by the
CRC
ALARM CH1 THRESHOLD
setting within the user-defined message count
CRC ALARM 1 CH1 COUNT
, the
DIR IO CH1 CRC ALARM
FlexLogic™ operand is set.
When the total message counter reaches the user-defined maximum specified by the
CRC ALARM CH1 MESSAGE COUNT
set-
ting, both the counters reset and the monitoring process is restarted.
The operand shall be configured to drive an output contact, user-programmable LED, or selected communication-based
output. Latching and acknowledging conditions - if required - should be programmed accordingly.
The CRC Alarm function is available on a per-channel basis. The total number of direct input/output messages that failed
the CRC check is available as the
ACTUAL VALUES STATUS DIRECT INPUTS CRC FAIL COUNT CH1(2)
actual value.
• Message Count and Length of the Monitoring Window: To monitor communications integrity, the relay sends 1
message per second (at 64 kbps) or 2 messages per second (128 kbps) even if there is no change in the direct out-
puts. For example, setting the
CRC ALARM CH1 MESSAGE COUNT
to “10000”, corresponds a time window of about 160
minutes at 64 kbps and 80 minutes at 128 kbps. If the messages are sent faster as a result of direct outputs activity, the
monitoring time interval will shorten. This should be taken into account when determining the
CRC ALARM CH1 MESSAGE
COUNT
setting. For example, if the requirement is a maximum monitoring time interval of 10 minutes at 64 kbps, then
the
CRC ALARM CH1 MESSAGE COUNT
should be set to 10
×
60
×
1 = 600.
• Correlation of Failed CRC and Bit Error Rate (BER): The CRC check may fail if one or more bits in a packet are cor-
rupted. Therefore, an exact correlation between the CRC fail rate and the BER is not possible. Under certain assump-
tions an approximation can be made as follows. A direct input/output packet containing 20 bytes results in 160 bits of
data being sent and therefore, a transmission of 63 packets is equivalent to 10,000 bits. A BER of 10
–4
implies 1 bit
error for every 10,000 bits sent/received. Assuming the best case of only 1 bit error in a failed packet, having 1 failed
packet for every 63 received is about equal to a BER of 10
–4
.
c) UNRETURNED MESSAGES ALARM CH1(2)
PATH: SETTINGS PRODUCT SETUP DIRECT I/O UNRETURNED MESSAGES ALARM CH1(2)
The L60 checks integrity of the direct input/output communication ring by counting unreturned messages. In the ring config-
uration, all messages originating at a given device should return within a pre-defined period of time. The Unreturned Mes-
sages Alarm function is available for monitoring the integrity of the communication ring by tracking the rate of unreturned
CRC ALARM CH1 CRC ALARM CH1
FUNCTION: Disabled
Range: Enabled, Disabled
MESSAGE
CRC ALARM CH1
MESSAGE COUNT: 600
Range: 100 to 10000 in steps of 1
MESSAGE
CRC ALARM CH1
THRESHOLD: 10
Range: 1 to 1000 in steps of 1
MESSAGE
CRC ALARM CH1
EVENTS: Disabled
Range: Enabled, Disabled
UNRETURNED
MESSAGES ALARM CH1
UNRET MSGS ALARM CH1
FUNCTION: Disabled
Range: Enabled, Disabled
MESSAGE
UNRET MSGS ALARM CH1
MESSAGE COUNT: 600
Range: 100 to 10000 in steps of 1
MESSAGE
UNRET MSGS ALARM CH1
THRESHOLD: 10
Range: 1 to 1000 in steps of 1
MESSAGE
UNRET MSGS ALARM CH1
EVENTS: Disabled
Range: Enabled, Disabled