User's Manual

SEL-3031 Instruction Manual Date Code 20091009
Performance Monitoring, Testing, and Troubleshooting
Monitoring Radio Performance
5.4
Monitoring MIRRORED BITS performance over a radio link is critical to ensure proper
operation when called upon to operate. The RBAD and CBAD bits provided in every
SEL device with M
IRRORED BITS can be used to alarm when the radio link is degraded
below levels needed for proper operation.
➤ RBADPU: Setting for the amount of time the channel is in a failed
state before setting the RBAD alarm Relay Word bit.
➤ CBADPU: Setting for the threshold of the CBAD channel availability
alarm.
When a M
IRRORED BITS channel is operating correctly, Relay Word bit ROK is set to
1. When the channel is disturbed, ROK drops out. The ROK bit is not recommended
for use as an alarm point. ROK is a good indication of the channel’s health. If the ROK
bit is toggling, this is an indication of an intermittent channel problem.
Figure 5.2 RBAD Generation
The RBAD bit is generated by the output of the RBAD timer. The RBAD timer is
driven by the ROK signal. RBAD is the recommended bit to indicate communications
alarms. Typically, a communications outage of two seconds or greater is considered an
alarm condition. RBAD should be set on both M
IRRORED BITS device to the maximum
length of outage before declaring an alarm.
The CBADPU setting is generated from the unavailability of the M
IRRORED BITS
channel. For example, if RBADPU is set to 2 seconds and the longest channel
disruption was 1 second out of every second and this occurred every 2 seconds, RBAD
would not assert. RBAD would not assert because M
IRRORED BITS is not disrupted for
longer than 2 seconds at any time. Relay Word bit CBAD and the CBADPU setting
solves this problem. To set CBADPU there are two good options. The first option is to
set it to 2000. This is a common value used based upon spread spectrum radio use in
the field. The CBAD Relay Word bit will assert when the unavailability of the channel
exceeds 0.02.
The other method in setting CBAD is to let the radio link run for a period of time and
monitor the performance. After reviewing a month of unavailability you will be able to
set CBADPU above the unavailability value.
The proper setting and use of CBAD and RBAD is important to report when the
communications link has failed or has become intermittent enough to cripple proper
communication. Over time, many issues can occur to cause a bad or intermittent radio
link. Items such as tree growth, new building construction, or another radio added at
MIRRORED BITS
Decoder and Integrity
Checks
ROK
RBAD
Timer
RBAD
Serial Data