Subject to change without notice
24
In-phase input voltages:
No invert function active = sum.
One invert function active = difference.
Both invert functions (if available) active = sum.
Antiphase input voltages:
No invert function active = difference.
One invert function active = sum.
Both invert functions (if available) active = difference.
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 measurement
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 most important control regarding this operation mode is the
DUAL - XY (19)
pushbutton (
please note section “Controls and
Readout”
).
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 deactivated. The
input deflection coefficient ranges are the same for both channels,
because the
X x10
magnifier 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 1M
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 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.
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.
Operating modes
