Operating Modes Of The Vertical Amplifiers In Yt Mode; X-Y Operation; Phase Comparison With Lissajous Figures - Hameg HM1507-3.02 Manual

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compensating wide-band attenuators or -amplifiers. In such
a case, the input of an appropriate circuit will be connected
to the CAL.-output via a suitable probe.
The voltage provided at a high-impedance input (1MΩ II 15-
30pF) will correspond to the division ratio of the probe used
(10:1 = 20mVpp output). Suitable probes are HZ51, 52, and
54.
Operating modes of the vertical
amplifiers in Yt mode
The most important controls regarding the operation modes
of the vertical amplifiers are the pushbuttons: CHI (22), DUAL
(23) and CH II (26). Their functions are described in the
section " Controls and Readout".
In most cases oscilloscopes are used to display signals in Yt
mode. Then the signal amplitude deflects the beam in vertical
direction while the time base causes an X deflection (from
left to right) at the same time. Thereafter the beam becomes
blanked and fly back occurs.
The following Yt operation modes are available:
Single channel operation of channel I (Mono CH I).
Single channel operation of channel II (Mono CH II).
Two channel operation of channel I and channel II (DUAL).
Two channel operation of channel I and channel II -displaying
the algebraic result as the sum or difference - (ADD).
The way the channel switching is determined in DUAL mode
depends on the time base setting and is described in the
section "Controls and Readout".
In ADD mode the signals of both channels are algebraically
added and displayed as one signal. Whether the resulting
display shows the sum or difference is dependent on the
phase relationship or the polarity of the signals and on the
invert function.
In ADD mode the following combinations are possible for
In-phase input voltages:
No invert function active = sum.
One invert function active = difference.
Both invert functions active = sum.
Anti-phase input voltages:
No invert function active = difference.
One invert function active = sum.
Both invert functions 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 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 most important control regarding this operation mode is
the DUAL - XY (23) pushbutton (please note section "Con-
trols and Readout").
Subject to change without notice

Operating modes of the vertical amplifiers in Yt mode

In XY mode the time base is deactivated. The signal applied
to the input of channel II - 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. II control is automatically
inactivated. 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 for-
mula, 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 vol-
tage. A CR network before the test voltage input of the
oscilloscope can help here. The 1 MΩ 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-cir-
cuited), 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.
29

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