GE L60 Instruction Manual

Also see for L60: Communications manual Communications guide Instruction manual Instruction manual Instruction manual

Contents

5-40 L60 Line Phase Comparison Relay GE Multilin5.2 PRODUCT SETUP 5 SETTINGS5b) CRC ALARM CH1(2)PATH: SETTINGS Ö PRODUCT SETUP ÖØ DIRECT I/O ÖØ CRC ALARM CH1(2)The L60 checks integrity of the incoming direct input/output messages using a 32-bit CRC. The CRC Alarm function isavailable for monitoring the communication medium noise by tracking the rate of messages failing the CRC check. Themonitoring function counts all incoming messages, including messages that failed the CRC check. A separate counter addsup messages that failed the CRC check. When the failed CRC counter reaches the user-defined level specified by the CRCALARM CH1 THRESHOLD setting within the user-defined message count CRC ALARM 1 CH1 COUNT, the DIR IO CH1 CRC ALARMFlexLogic™ 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-basedoutput. 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 failedthe CRC check is available as the ACTUAL VALUES Ö STATUS ÖØ DIRECT INPUTS ÖØ CRC FAIL COUNT CH1(2) actual value.• Message Count and Length of the Monitoring Window: To monitor communications integrity, the relay sends 1message 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 160minutes at 64 kbps and 80 minutes at 128 kbps. If the messages are sent faster as a result of direct outputs activity, themonitoring time interval will shorten. This should be taken into account when determining the CRC ALARM CH1 MESSAGECOUNT setting. For example, if the requirement is a maximum monitoring time interval of 10 minutes at 64 kbps, thenthe 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 ofdata being sent and therefore, a transmission of 63 packets is equivalent to 10,000 bits. A BER of 10 –4 implies 1 biterror for every 10,000 bits sent/received. Assuming the best case of only 1 bit error in a failed packet, having 1 failedpacket for every 63 received is about equal to a BER of 10 –4.c) UNRETURNED MESSAGES ALARM CH1(2)PATH: SETTINGS Ö PRODUCT SETUP ÖØ DIRECT I/O ÖØ 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 CH1CRC ALARM CH1FUNCTION: DisabledRange: Enabled, DisabledMESSAGE CRC ALARM CH1MESSAGE COUNT: 600Range: 100 to 10000 in steps of 1MESSAGE CRC ALARM CH1THRESHOLD: 10Range: 1 to 1000 in steps of 1MESSAGE CRC ALARM CH1EVENTS: DisabledRange: Enabled, Disabled UNRETURNED MESSAGES ALARM CH1UNRET MSGS ALARM CH1FUNCTION: DisabledRange: Enabled, DisabledMESSAGE UNRET MSGS ALARM CH1MESSAGE COUNT: 600Range: 100 to 10000 in steps of 1MESSAGE UNRET MSGS ALARM CH1THRESHOLD: 10Range: 1 to 1000 in steps of 1MESSAGE UNRET MSGS ALARM CH1EVENTS: DisabledRange: Enabled, Disabled