Hameg HM 1004-3 Series, Руководство пользователя

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Subject to change without notice
First Time Operation
Operating modes of the
vertical amplifiers in Yt mode
The most important controls regarding the operation modes
of the vertical amplifiers are the pushbuttons:
CH I (17) ,
DUAL (18) and CH II (21) . 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 timebase 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 timebase 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 (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 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 (18) pushbutton ( please note section “Con-
trols and Readout” ).
In XY mode the timebase 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 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. Calcu-
lation 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 func-
tions, 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.