When IRIG-B data acquisition is activated, either manually with the IRIG command or
automatically, two consecutive frames are taken. The older frame is updated by one second,
then the frames are compared. If the frames do not agree, the data are considered erroneous
and discarded.
Automatic execution is invoked about once every five minutes. The relay stops IRIG-B data
acquisition ten minutes before midnight on New Year’s Eve and restarts acquisition twenty
minutes later. IRIG-B data acquisition is halted so the system clock may implement the year
change without interference from the IRIG-B clock.
Self Tests
The relay runs a variety of self tests. Some tests have warning and failure states; others only
have failure states. The relay generates a report after any change in self test status.
The relay closes the ALARM contacts after any self test fails. When it detects certain
failures, the relay disables the breaker control functions and places the relay output driver port
in an input mode. No outputs may be asserted when the instrument is in this configuration.
The relay runs all self tests on power up and before enabling new settings. During normal
operation, it performs self tests at least every few minutes.
Offset
The relay measures the offset voltage of each analog input channel and compares the value
against fixed limits. It issues a warning when offset is greater than 50 millivolts in any
channel and declares a failure when offset exceeds 75 millivolts. Offset levels for all channels
appear in the STATUS command format.
Power Supply
Power supply voltages are limit-checked. The table below summarizes voltage limits.
Table 2.5: Power Supply Self Test Limits
Supply
Warning Thresholds
Failure Thresholds
+5 V
+5.3 V +4.7 V
+5.4 V +4.6 V
+ 15 V
+ 15.8 V + 14.2 V
+ 16.2 V + 13.8 V
-15 V
-15.8 V
-14.2 V
-16.2 V
-13.8 V
Date Code 920508
Specifications
SEL-221F, -1 Instruction Manual
2-29
Summary of Contents for SEL-221F
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Page 158: ...SETTINGS SHEET FOR SEL 221F RELAY PAGE 2 OF 6 DATE Date Code 921110 ...
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