1250 Frequency Response Analyzer Break, Self Test, Time Display and Power Fail
AMK/1250/3 14-5
14.4 POWER FAIL
The 1250 contains a circuit which detects any interruption to the mains supply, whether
deliberate or accidental. When a mains failure is detected, the control circuitry adds up
the "bits" of data in selected parts of the memory, and stores the result as a number,
called the “check sum". The memory circuits are switched to battery operation, so that
all the data in them, plus the check sum, are preserved for at least 100 hours.
When the mains supply is restored, a new check sum calculation is made, and the result
compared with the original check sum. If the two agree, the Display will be as in Fig.
14.6:
Fig. 14.6 - Power Restored Display
This signifies that the 1250 has correctly remembered all the menu settings from the last
time it was used. Therefore, after the Generator, Analyzers, etc. have been restarted,
the instrument may continue to be used as if it had not been switched off.
The TIME display, in hours, minutes and seconds, shows time elapsed since the
instrument was switched on, starting from zero. The time-of-day can be entered in this
display from the Front Panel, as described in Section 3, or from a peripheral device.
If the check sums do not agree, the Display will be as in Fig. 14.7:
Fig. 14.7 - Initialised Display
This signifies that errors have been detected in the previous 1250 settings. Therefore
the control circuitry has erased the contents of the parameter store and returned all
settings to their default state. The contents of the File and the Learnt Program store
have also been erased.
The TIME display is reset to zero, as in "POWER RESTORED". If the mains is
interrupted whilst a measurement, or any other operation, is in progress, that operation
stops at once and will not be automatically completed when power is restored. The
1250 recognises loss of mains for greater than 10 milliseconds as a mains failure;
shorter interruptions are ignored.
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