Operation
DA1855A-OM-E Rev A
ISSUED: July 2002
3-7
PVG absolute mode
: DA1855 PVG increment and decrement
buttons always function to increment or decrement the
voltage
display
respectively. When decrementing from a positive voltage,
the display always stops at zero. To obtain negative voltages, the
±±
button must be pushed, and the increment button is used to
increase the magnitude of the negative voltage. This operation is
natural if simply setting a voltage, but unnatural if moving a
displayed oscilloscope waveform. This is known as the PVG
absolute mode, and the only mode available in the original
DA1855, (non “A” model). The DA1855A retains the option of
operating in this same manner as well as supporting PVG roll
through zero mode.
Note:
When the DA1855A is controlled remotely through a
LeCroy oscilloscope, neither PVG absolute or PVG roll
through zero modes apply. When operated remotely, the
PVG value is controlled with the use of the OFFSET knob
on the oscilloscope, when in effect, operates in the roll
through mode.
PVG roll through zero mode:
The DA1855A increment buttons
are oscilloscope waveform related by factory default. The
increment buttons move a displayed oscilloscope waveform
upward and the decrement buttons move the waveform
downward independent of the PVG polarity. Decrements from a
positive voltage will roll smoothly through zero. This is known as
roll through zero mode.
Toggle PVG modes:
To change from roll through zero to
absolute mode of operation hold the PVG ZERO button and
press the
±
button. Change back to the roll through zero mode by
repeating the same operation.
Differential Offset
V
DIFF
(differential offset voltage) is an instrument mode rather
than a type of input coupling. The
V
DIFF
mode allows the PVG to
inject a calibrated offset signal into the DA1855A while still using
both inputs for full differential operation. This mode can be used
as a position control to move the trace on the oscilloscope screen
in preference to using the oscilloscope's position or offset control.
The oscilloscope's position and offset controls should always be
set to zero so that the DA1855A's dynamic range is properly
centered. (This is done automatically when using a LeCroy
oscilloscope with ProBus interface.) When the oscilloscope is set
to greater sensitivities (lower Volts/Div settings), the Differential
