25
Subject to change without notice
Antiphase input voltages:
No invert function active = difference.
Channel II invert function active = sum.
In the
ADD
mode the vertical display position is dependent
upon the
Y-POS.
setting of both channels. The same Y
deflection coefficient is normally used for both channels with
algebraic addition.
Please note that the
Y-POS.
settings are also added but are not
affected by the
INV
setting.
Differential measurement techniques allow direct measure-
ment of the voltage drop across floating components (both
ends above ground). Two identical probes should be used for
both vertical inputs. In order to avoid ground loops, use a
separate ground connection and do not use the probe ground
leads or cable shields.
X-Y Operation
The important control for this mode is the pushbutton labeled
DUAL
and
XY (22)
. The following description refers to the
XY
analog mode.
In
XY
mode the time base is deactivated. The signal applied to
the input of channel I - front panel marking
HOR. INP. (X)
-
causes the X deflection. The input related controls (
AC/DC
,
GD
pushbutton and the
VOLTS/DIV
knob) consequently
affect the X deflection. For X position alteration, the X-POS.
control knob must be used, as the
Y-POS. I
control is
automatically inactivated. The input deflection coefficient ranges
are the same for both channels, because the
X-MAG x10
function is inactive in XY mode.
The bandwidth of the X amplifier, is lower than the Y amplifier
and the phase angle which increases with higher frequencies,
must be taken into account (please note data sheet).
The inversion of the X-input signal is not possible.
Lissajous figures can be displayed in the X-Y mode for certain
measuring tasks:
• Comparing two signals of different frequency or bringing
one frequency up to the frequency of the other signal. This
also applies for whole number multiples or fractions of the
one signal frequency.
• Phase comparison between two signals of the same
frequency.
Phase comparison with Lissajous figures
The following diagrams show two sine signals of the same
frequency and amplitude with different phase angles.
Calculation of the phase angle or the phase shift between the
X and Y input voltages (after measuring the distances a and b
on the screen) is quite simple with the following formula, and
a pocket calculator with trigonometric functions. Apart from
the reading accuracy, the signal height has no influence on the
result.
The following must be noted here:
• Because of the periodic nature of the trigonometric functions,
the calculation should be limited to angles
≤
90°. However
here is the advantage of the method.
• Due to phase shift, do not use a too high test frequency.
• It cannot be seen as a matter of course from the screen
display if the test voltage leads or lags the reference
voltage. A CR network before the test voltage input of the
oscilloscope can help here. The 1 M
Ω
input resistance can
equally serve as R here, so that only a suitable capacitor C
needs to be connected in series. If the aperture width of the
ellipse is increased (compared with C short-circuited), then
the test voltage leads the reference voltage and vice versa.
This applies only in the region up to 90° phase shift.
Therefore C should be sufficiently large and produce only a
relatively small just observable phase shift.
Should both input voltages be missing or fail in the X-Y
mode, a very bright light dot is displayed on the screen.
This dot can burn into the phosphor at a too high
brightness setting (INTENS. knob) which causes either
a lasting loss of brightness, or in the extreme case,
complete destruction of the phosphor at this point.
Phase difference measurement
in DUAL mode (Yt)
Phase differences between two input signals of the same
frequency and shape can be measured very simply on the
screen in Dual mode. The time base should be triggered by the
reference signal (phase position 0). The other signal can then
have a leading or lagging phase angle. In alternate triggering
condition, phase difference measurement is not possible. For
greatest accuracy adjust the time base for slightly over one
period and approximately the same height of both signals on
the screen. The Y deflection coefficients, the time base
coefficients and the trigger level setting can be used for this
adjustment, without influence on the result. Both base lines
are set onto the horizontal graticule center line using the Y-
POS. knobs before the measurement. With sinusoidal signals,
observe the zero (crossover point) transitions; the sine peaks
are less accurate. If a sine signal is noticeably distorted by even
harmonics, or if a DC voltage is present, AC coupling is
recommended for both channels. If it is a question of pulses
of the same shape, read off at steep edges.
It must be noted that the phase difference cannot be determined
if alternate triggering is selected.
Phase difference measurement in DUAL mode
t = horizontal spacing of the zero transitions in div
T = horizontal spacing for one period in div
Operating modes of the vertical amplifiers in Yt mode
