Tektronix 222 Operator's Manual page 83

Makina Measurements-222 DSO Operators
Voltage with respect to ground is found by first setting a ground ref-
erence level. Select GND coupling for the measurement channel and
position the baseline trace to a reference graticule line. If the signal
being measured is positive with respect to ground, the bottom
graticule line makes a good ground reference. After setting the
position of ground, switch to DC coupling to make the measurement.
Do not change Vertical POSITION setting after switching back to DC
coupling or you will lose your ground reference.
Find the number of vertical divisions from the ground reference to the
measurement point on the signal and multiply by the VOLT/DIV set-
ting. The result is thevoltage at the measurement point with respect to
ground.
In the figure 5-2, the ground level reference is the bottom graticule
line. From the ground reference to the most negative point on the
signal is
3.5
divisions up. Multiplying that number by the
5 V
per
division scale factor gives a dc level of 17.5 V at the measurement
point.
GROUND
REFERENCE
LINE
Figure 5-2. Voltage with respect to ground.