GE Multilin D30 Line Distance Relay 5-495 SETTINGS 5.2 PRODUCT SETUP5monitoring 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 D30 checks integrity of the direct input/output communication ring by counting unreturned messages. In the ring con-figuration, all messages originating at a given device should return within a pre-defined period of time. The UnreturnedMessages Alarm function is available for monitoring the integrity of the communication ring by tracking the rate of unre-turned messages. This function counts all the outgoing messages and a separate counter adds the messages have failedto return. When the unreturned messages counter reaches the user-definable level specified by the UNRET MSGS ALARMCH1 THRESHOLD setting and within the user-defined message count UNRET MSGS ALARM CH1 COUNT, the DIR IO CH1 UNRETALM FlexLogic™ operand is set.When the total message counter reaches the user-defined maximum specified by the UNRET MSGS ALARM CH1 MESSAGECOUNT setting, 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 Unreturned Messages Alarm function is available on a per-channel basis and is active only in the ring configuration.The total number of unreturned input/output messages is available as the ACTUAL VALUES Ö STATUS ÖØ DIRECT INPUTSÖØ UNRETURNED MSG COUNT CH1(2) actual value. 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
