Tektronix 7A19 Instruction Manual page 10

Operating Instructions-7A19
trace to the top graticule line . Do not move the POSITION
control after this reference line has been established .
4. Set the Coupling switch to DC . The ground reference
line can be checked at any time by switching to the GND
position .
5 . Set the time-base Triggering controls for a stable
display. Set the Time Base sweep rate for an optimum
display of the waveform .
6 . Measure the distance
in divisions between the
reference line and the point on the waveform at which the
DC level is to be measured . For example, in Fig . 2-2 the
measurement is between the reference line and point A.
7 . Establish the polarity of the waveform . With the
POLARITY switch in the NORM position, any point above
the reference line is positive .
8. Multiply the distance measured in step 6 by the
VOLTS/DIV switch setting . Include the attenuation factor
of the probe, if used .
EXAMPLE : Assume the vertical distance measured is
3.6 divisions (see Fig . 2-2) and the waveform is above the
reference line, using a 10X probe with a VOLTS/DIV
switch setting of 0.5 V .
Using the formula :
Instan- vertical VOLTS/ probe
taneous = distance X polarity X DIV X attenuation
voltage
(divisions) setting factor
Substituting the given values :
The instantaneous voltage is 18 volts.
Matching transit times using two 7A19's, one
having VARIABLE DELAY (Option 4)
In some applications it is necessary to view the time
relationship of two signals, one with respect to the other.
2-4
NOTE
To measure a voltage level with respect to another
voltage rather than ground, make the following
changes to Step 4. Set the Coupling switch to DC and
apply the reference voltage to the INPUT connector.
Then position the trace to the reference line and
disconnect the reference voltage.
Instantaneous Voltage = 3.6 X 1 X 0 .5 V X 10
Fig. 2-2. Measuring instantaneous voltage with respect to same
reference.
With high speed signals, the transit times of the probes and
amplifiers can distort the true time relationship of the two
signals . By using the VARIABLE DELAY (Option 4), the
transit times between two units can be matched to within
50 ps, thus giving a true time relationship of the signals
being viewed .
For matching transit times of two 7A19 with probes,
proceed as follows:
1 . Install the 7A19 without the VARIABLE DELAY
option in the left vertical plug-in compartment.
2 . Install the 7A19 with VARIABLE DELAY option in
the right vertical plug-in compartment.
3 . Connect the probes to a common signal source of
greater than 100 kHz and adjust the time-base unit for the
fastest sweep available.
4. Set the Trigger Source switch to left Vert, and
Vertical Mode to Alternate.
5. Set both 7A19's to the same deflection factor
settings .
6. Center both displays vertically .
7 . Adjust VARIABLE DELAY so that the two displays
are superimposed . The transit times of both units are now
matched .