Additional Generator Controls 1250 Frequency Response Analyzer
9-8 AMK/1250/2
9.2.4 SETTING THE MENU
To set up the Amplitude Compression facility, press GENERATOR MENU, then operate
the SELECT key until the Display shows [AMPL. COMPRESS] MENU. Five soft keys
will be assigned as follows:
SOURCE. The SELECT key allows either Channel 1 or Channel 2 to be allocated as
the control Channel, whichever is the most convenient to the user. The default state
selects Channel 1, which is useful if a point to point measurement is to be made.
Connect the input of the selected Channel to the point to be monitored.
VALUE. Enter the nominal value of the voltage that it is desired to maintain at the
monitored point.
ERROR%. Enter the percentage error that can be tolerated on the nominal voltage.
This figure often has to be a compromise. Whilst it is usually desirable to keep the error
as small as possible, it may be necessary to accept a wider tolerance, for reasons
discussed in Section 2.5.
LIMIT. Enter the safe operating Generator output voltage limit required.
COMPRESS. This key acts as the on/off control, the default state being "off”. Enter
"on" if the Amplitude Compression facility is required.
9.2.5 ERROR 84
Section 9.2.2 describes how ERROR 84 will be displayed if the corrected Generator
output still yields a wrong signal level at the monitored point. This can occur if the 1250
bases its correction ratio calculation on unsuitable data, and may necessitate increasing
the % ERROR value. There are three main reasons why the data may be unsuitable:
1. Excessive noise on the signal. The effect of this can be reduced by increasing
the ∫ TIME value.
2. The system under test parameters are not stable, e.g. the gain changes with
time.
3. The amplitude response of the system under test is non-linear.
When ERROR 84 appears in the Display during a Sweep with Amplitude Compression
on, a warning "beep" will sound. The Sweep is continued but ERROR 84 remains
displayed as a warning that there has been at least one non-valid reading. Any further
non-valid readings will also generate a "beep".
9.2.6 USE OF THE FILE
If a Sweep is left to run unattended, and the user wishes to know which, if any, readings
produced ERROR 84, all the readings should be stored in the File, as explained in
Chapter 12. These readings can then be replayed at a later date, as many times as
necessary, for analysis.
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