15
with the cursor in the most significant digit, the rotary control will decrement the offset in 100mV
steps as follows:
program = +205 mVdc
program = +105 mVdc
program = +005 mVdc
program =
−
095 mVdc
program =
−
195 mVdc
The actual DC offset at the MAIN OUT socket is attenuated by the fixed
−
step output attenuator
when this is in use. Since it is not obvious when the signal is being attenuated the actual offset is
shown in brackets as a non
−
editable field below the programmed value.
For example, if the amplitude is set to 2·5Vpp the output is not attenuated by the fixed attenuator
and the actual DC offset (in brackets) is the same as that set. The
DC OFFSET
display shows:
DC OFFSET
p1.50 Vdc
(1.50 Vdc)
◊
srce:50
Ω
load:hiZ
◊
If the amplitude is now reduced to 250mVpp which introduces the attenuator, the actual DC offset
changes by the appropriate factor:
DC OFFSET
p1.50 Vdc
(151 mVdc)
◊
srce:50
Ω
load:hiZ
◊
The above display shows that the set DC offset is +1.50V but the actual offset is +151mV.
Note that 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 250mVpp exactly and takes account of the small error in the
fixed attenuator; the offset is 151.mV exactly, taking account of the effect of the known
attenuation (slightly less than the nominal) on the set offset of 1.50V.
Whenever the set DC offset is modified by a change in output level in this way a warning
message that this has happened will be displayed. Similarly, because waveform clipping occurs if
the DC offset plus signal peak exceeds ± 10V, a warning message will be displayed if this
condition is set. This is explained more fully in the Warnings and Error Messages section.
When
dc only
is selected on the
WAVEFORM
screen the output ‘waveform’ is the baseline
DC voltage only, set from this screen. Since there is no switching waveform, the DC level can be
set over the full ± 10V range; the attenuator is automatically used to give a setting resolution
down to 1mV below 1Vdc and the
actual
value will always match the
program
value.
The source impedance and assumed load can also be set from this screen.
Symmetry
SYMMETRY 50%
♦
◊
20% 60%
◊
◊
30% 50 % 70%
◊
◊
40% 80%
◊
Pressing
SYMMETRY
on the Main menu gives the SYMMETRY screen.
