Teledyne LeCroy DA1855A - Manual (Page 35)

Operator’s Manual
922258-00 Rev A 29
Set the Function generator’s output to 50 kHz and 100 mVp-p sine wave and the output connected
to the DA1855’s +INPUT.
Set the oscilloscope to 5 mV/div and time/div adjusted to display 2 to 3 cycles.
Externally trigger the oscilloscope by connecting a cable from the function generator’s output (same
signal as is applied to the DA1855A's +INPUT) or from the Trigger Signal out on the oscilloscope.
Under these conditions, the negative peak of the display on the oscilloscope should be very near
center screen. Adjust the OFFSET knob on the oscilloscope until the negative peak is at center
screen.
Select V
DIFF
in the PVG Mode window. This internally applies the output of the Precision Voltage
Generator to a point within the DA1855A's amplifier that facilitates a true differential offset. The
V
COMP
light went out and the OFF light was lighted. In the line under the Precision Voltage Generator
display (COMPARISON or DIFFERENTIAL OFFSET ), the COMPARISON light went out and the
DIFFERENTIAL light was lighted. This indicates that the Precision Voltage Generator will now be
applied as a differential offset rather than as a comparison voltage as in the previous exercise. Both
the +INPUT and the –INPUT inputs are now enabled, even though the –INPUT OFF light is still ON.
The positive and negative peaks of the waveform displayed on the oscilloscope are (respectively) 10
divisions above and below the display center line. Rotate the OFFSET knob above the VOLTS/DIV
knob on the oscilloscope until the positive peak of the waveform appears in the oscilloscope’s
display. Continue adjusting the oscilloscope’s OFFSET knob until the peak of the waveform is at the
centerline of the oscilloscope’s display. The number in the Precision Voltage Generator display is the
waveform’s positive peak voltage.
Rotate the OFFSET knob clockwise until the negative peak of the signal is now at or near the
oscilloscope’s display centerline. By adjusting the OFFSET knob, the negative peak can be positioned
to the oscilloscope’s display centerline. Now the number in the Precision Voltage Generator’s
display is the waveform’s negative peak voltage.
Change the oscilloscope’s sensitivity from 5 mV/div to 1 mV/div. Select Auto Zero in the List Select
menu and push the button next to Auto Zero window to cause the DA1855A to adjust its DC
balance.
Change the OFFSET control to again place the negative peak of the waveform at the oscilloscope’s
center screen. Note that the Precision Voltage Generator’s display represents the negative peak
voltage of the waveform with greater resolution.
Return the oscilloscope’s sensitivity to 50mV/div and select OFF in the PVG Menu. The Precision
Voltage Generator will retain its setting and the display on the oscilloscope will be centered about
the centerline.