Voltage Comparison Measurements - Tektronix 3A6 Instruction Manual

2. Connect the signal to either input connector.
3. Set the MODE switch to the channel used.
4. Set the AC DC GND switch to GND.
5, Adjust the triggering controls for automatic triggering.
6. Align the trace with the bottom line of the graticule or
other reference line. If the voltage is negative with respect
to ground, set the INV (CH 1} NORM switch to INV and then
align the trace with the reference line. Do not move the
POSITION control after this reference line has been estab-
lished.
NOTE
To measure a voltage level with respect to another
voltage rather than ground, make the following
changes in the above procedure. Set the AC DC
GND switch to DC. Apply the reference voltage to
the input and position the trace to the reference
line,
7. Set the AC DC GND switch to DC. The ground ref-
erence can be checked at any time by switching to the GND
position.
8. Set the time-base triggering controls to obtain a stable
display. Set the time/division switch to a setting that will
display several cycles of the waveform.
9, Measure the distance in divisions between the ground
reference line established in step 6 and the point on the
waveform to be measured. For example, in Fig. 2-2 the
measurement is made between points (a} and (b).
(a)
Vertical
Distance {b)
Reference line
Fig. 2-2. Measuring instantaneous de voltage with respect to a ref-
erence,
10. Establish the polarity of the signal. If the waveform
is above the reference line with the INV (CH 1] NORM switch
set to NORM, the voltage is positive. If the INV (CH 1}
NORM switch is set to INV, the voltage is negative.
11. Multiply the distance measured in step 8 (include
polarity) by the VOLTS/DIV setting. Include the attenuation
factor of the probe, if any.
@1
Operating Instructions—Type 3A6
As an example of this method of measurement, assume
that the vertical distance is 4.6 divisions (see Fig. 2-2), INV
(CH 1) NORM switch set to INV, using a 10 probe and a
VOLTS/DIV setting of 2.
Using the formula:
Instantaneous __
Voltage
vertical probe
distance X polarity X vO X attenuation
(divisions) sering factor
Substituting the values given above:
Instantaneous Voltage = 4.6 X —1 X 2 X 10
The instantaneous voltage would be —92 volts.
Voltage Comparison Measurements
In some applications it may be necessary to establish a set
of deflection factors other than those indicated by the
VOLTS/DIV switch. This is useful for comparing signals which
are exact multiples of a reference voltage amplitude. To
establish a set of deflection factors based upon some specific
reference amplitude, proceed as follows:
1. Apply a reference signal of known amplitude to the
Channel 1 input connector and adjust the size of the display
for an exact number of graticule divisions using the Channel
1 VOLTS/DIV switch and VARIABLE control. Do not move
the VARIABLE conirol after obtaining the desired deflection.
2. Divide the amplitude of the reference signal (volts) by
the product of the deflection in divisions (established in step
1) and the VOLTS/DIV switch setting. This is the Deflection
Conversion Factor.
ellection _ Reference signal amplitude (volts)
Factor Deflection (divisions) X VOLTS/DIV setting
3. To calculate the Adjusted Deflection Factor at any set-
ting of the Channel 1 VOLTS/DIV switch, multiply the VOLTS/
DIV switch setting by the Deflection Conversion Factor
obtained in step 2.
Adjusted
Deflection = VOLTS/DIV setting X Deflection Conversion
Factor Factor
This Adjusted Deflection Factor applies only to Channel 1 —
and is correct only if the VARIABLE control is not moved from
the position set in step 1.
4, To determine the peak-to-peak amplitude of a signal
compared to a reference, disconnect the reference and apply
the signal to Channel 1.
5. Set the Channel 1 VOLTS/DIV switch to a setting that
will provide sufficient deflection to make the measurement.
Do not readjust the VARIABLE control.
6. Measure the vertical deflection in divisions and deter-
mine the amplitude by the following formula:
. Adjusted :
ABpltude — Deflection X iicion)
Factor
As an example of this method of measurement, assume a
reference signal amplitude of 30 volts, a VOLTS/DIV setting
2-5