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2 Functions
2.28
Measurement Supervision
The device is equipped with extensive monitoring capabilities - both hardware and
software. In addition, the measured values are also constantly checked for plausibility,
so that the current and voltage transformer circuits are largely integrated into the mon-
itoring.
2.28.1 Functional Description
Hardware Monitoring
The device is monitored from the measurement inputs to the output relays. Monitoring
circuits and processor check the hardware for malfunctions and inadmissible condi-
tions (see also Table 2-7).
Auxiliary and Refer-
The processor voltage of 5 V DC is monitored by the hardware since if it goes below
ence Voltages
the minimum value, the processor is no longer functional. The device is under such a
circumstance removed from operation. When the normal voltage returns, the proces-
sor system is restarted.
Failure or switching off the supply voltage removes the device from operation and a
message is immediately generated by the "life contact" (an alternatively NO or NC
contact). Brief auxiliary voltage interruptions of less than 50 ms do not disturb the op-
erational readiness of the device (for nominal auxiliary voltage ≥ 110 VDC).
The processor monitors the offset and reference voltage of the ADC (analog-digital
converter). The protection is suspended if the voltages deviate outside an admissible
range; prolonged deviations are reported (indication: "Error A/D-conv.").
Battery
The buffer battery, which ensures operation of the internal clock and storage of
counters and messages if the auxiliary voltage fails, is periodically checked for charge
status. On its undershooting a minimum admissible voltage, the "Fail Battery"
indication is issued.
If the device is isolated from the auxiliary voltage for several hours, the internal back-
up battery is switched off automatically, i.e. the time is not registered any more. Mes-
sages and fault recordings however are kept stored.
Memory Modules
The working memory (RAM) is tested when the system is started up. If a malfunction
occurs then, the starting sequence is interrupted and an LED blinks. During operation,
the memory is checked using its checksum.
For the program memory, the cross sum is formed cyclically and compared to the
stored program cross sum.
For the settings memory, the cross sum is formed cyclically and compared to the cross
sum that is freshly generated each time a setting process takes place.
If a malfunction occurs, the processor system is restarted.
Sampling
Sampling and the synchronization between the internal buffer components are con-
stantly monitored. If any deviations cannot be removed by remedied synchronization,
then the processor system is restarted.
166
7UM61 Manual
C53000-G1176-C127-3
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