Product Manual

Standard Waveforms
Warning and Error Messages 5
DC OFFSET:
program +1.5
0 Vdc
(actual +151 mVdc)
load: hiZ
The above display shows that the set dc offset is +1.50 V but the actual offset is
+151 mV.
Note
The actual offset value also takes into account the true attenuation provided
by the fixed attenuator, using the values determined during the calibration
procedure. In the example displayed the output signal is 250 mV p-p
exactly and takes account of the small error in the fixed attenuator; the
offset is 151 mV (to three significant figures) and takes account of the effect
of the calibrated attenuation error on the set offset of 1.50 V.
Whenever the set dc offset is modified by a subsequent change in output level the display
shows a warning message. Similarly, settings which would result in peak offset+signal
levels outside the range ±10 V (and therefore clipping) generate a similar warning
message. There is additional information on these messages in the Warnings and Error
Messages section below.
The output attenuation is controlled intelligently to minimize the difference between the
programmed and actual offset when the combination of programmed amplitude and
offset allows this. Thus when the offset is set to 150 mV, for example, the amplitude can
be reduced to nominally 50 mV p-p before the fixed attenuator causes the actual offset to
be different from the programmed value.
Warning and Error Messages
Two classes of message are displayed on the screen when an illegal combination of
parameters is attempted.
WARNING messages are shown when the entered setting causes some change which the
user might not necessarily expect, as in the following two examples:
1. Changing the amplitude from, for example, 2·5 V p-p to 25 mV p-p brings in the step
attenuator; if a non-zero offset has been set then this will also be attenuated. The
message DC offset changed by amplitude will be shown temporarily
on the screen but the setting will be accepted; in this case the actual attenuated offset
will be shown in brackets below the set value.
2. With the output level set to 10 V p-p, increasing the dc offset beyond ±5 V will cause
the message Offset + Sum + level may cause clipping. The offset
change will be accepted (producing a clipped waveform) and the user may then
choose to change the output level or the offset to produce a signal which is not
clipped. The word (clip?) will show in the display beside AMPLITUDE or
DC OFFSET while the clipped condition exists.
ERROR messages are shown when an illegal setting is attempted, most generally a
number outside the range of values permitted. In this case the entry is rejected and the
parameter setting is left unchanged, as in the following three examples:
1. Entering a frequency of 1 MHz for a triangle waveform. The error message:
Frequency out of range for the selected waveform is
shown.
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