Operating Modes Of The Vertical Amplifier; Xy Mode; Measurement Of Phase Differences In Dual Channel Operation; Betriebsarten Der Vertikalverstärker - Hameg HM400 Manual

O p e r a t i n g m o d e s o f t h e v e r t i c a l a m p l i f i e r

5 Operating modes of the vertical amplifier

The most important controls determining the operating modes of the
vertical amplifer are the mode buttons CH 1, CH 2, DUAL, ADD and
32
XY .
Changing the modes is described in the chapter Controls. Yt is by far
the mode most used: the input signal deflects the trace vertically while
a time base moves the trace from left to right. The Y amplifier offers
these modes:
1. Single channel operation of CH 1.
2. Single channel operation of CH 2.
3. DUAL trace two channel operation.
4. Algebraic addition of CH 1 + CH 2 and subtraction of CH 1 – CH 2.
In DUAL trace mode both channels are operating, the time base de-
termines the exact mode of representation, see the chapter Controls.
Switching of the channels may either happen alternately after the com-
pletion of each time base cycle, or the switching occurs at a high rate
during the course of a time base cycle (chopped). The alternating mode
is unsuited at slow time bases because the alternation becomes visible
with disturbing flicker, here, the chopped mode will yield a flicker-free
display. At high sweep speeds the chopped mode is unsuited because
the switching transients are disturbing.
In the ADD mode the signals of both channels are algebraically added
(CH 1 + CH 2) or subtracted (CH 1 – CH 2) if CH 2 is inverted. If the si-
gnals of CH 1 and CH 2 happen to be of opposite phase they may fully
or partly cancel, of course.
It is important to bear in mind that the two inputs of the scope are not
to be mistaken as the inputs of a true difference amplifier! When using
this feature to measure the difference signal between two measuring
points, restrictions must be observed: both input attenuators must
be switched to the same setting, the common mode rejection is very
moderate, and the common mode range is limited to the normal
operating range of the input amplifiers. This means in practice that,
before the ADD mode is entered, it has to be checked whether each
input signal can be displayed, i.e. that is in within the normal operating
range; if that is the case for both signals, switch to ADD. Please note
further that both POSITION controls affect the vertical position of the
added signals. If probes are used, their tolerances will also diminish
the common mode rejection; this can be checked by connecting both
probes to the same measuring signal, the resulting display should
be zero. It is preferable to use the probe adjust or a pulse generator
for this test.
5.1

XY mode

For this mode use the button XY as described in the chapter Controls
under .
32
In this mode the time base is disabled. The CH1 input signal will deflect
the trace horizontally, the CH 2 input signal vertically. The horizontal
position is controlled as usual with the X-POSITION control
position control is disabled. The magnifier is also disabled. When using
this mode, the low bandwidth of the X amplifier (see the specifications)
has to be observed, the phase difference between the wide band vertical
amplifier and the X amplifier increases with frequency.
The Y signal may be inverted by pressing the button INV
CH 2.
Using Lissajous patterns it is possible
– to compare two signals of different frequency and to adjust one to
the frequency of the other until both are synchronized. This applies
also to multiples or fractions of one of the frequencies
– to measure the phase difference between two signals of the same
frequency.
34 Subject to change without notice
5.2 Measurement of phase differences in dual chan-
Betriebsarten der Vertikalverstärker
nel operation
A much more precise and convenient method of measuring phase
differences which is also applicable up to high frequencies is the mea-
Die für die Betriebsarten der Vertikalverstärker wichtigsten Bedienele-
surement of the time difference in dual channel operation. Please note:
mente sind die Mode Tasten: CH1, CH2, DUAL, ADD und XY
It is mandatory that the trigger signal is taken from only one signal.The
phase difference can be easily calculated as the frequency is known.
Die Betriebsartenumschaltung ist im Abschnitt "Bedienelemente"
Another advantage of this method is the
beschrieben. Die gebräuchlichste Art
fact that the time difference is still mea-
der mit Oszilloskopen vorgenommenen
surable even if the signals are corrupted
Signaldarstellung ist der Yt-Betrieb. In
by hum, ripple or noise. Also, there are
dieser Betriebsart lenkt die Amplitude
no ambiguities. Alternatively Lissajous
des zu messenden Signals (bzw. der
patterns can be used for measurement
Signale) den Strahl in Y-Richtung ab.
of phase differences.
Gleichzeitig wird der Strahl von links
nach rechts abgelenkt (Zeitbasis). Der
bzw. die Y-Messverstärker bietet/bieten
dabei folgende Möglichkeiten:
1. Die Darstellung nur eines Signals im Kanal 1-Betrieb.

6 Triggering and time base

2. Die Darstellung nur eines Signals im Kanal 2-Betrieb.
3. Die Darstellung von zwei Signalen im DUAL-Betrieb (Zweikanal).
4. Die Darstellung eines Signals, welches aus der algebraischen
Summe oder Differenz (Addition) von zwei Signalen resultiert.
The pertinent controls are located to the right of the VOLTS/DIV knobs,
see the chapter Controls.
Bei DUAL-Betrieb arbeiten beide Kanäle. Die Art, wie die Signale beider
Kanäle dargestellt werden, hängt von der Zeitbasis ab (siehe „Bedien-
In Yt operation the signal deflects the trace vertically while it is deflected
elemente"). Die Kanalumschaltung kann nach jedem Zeit-Ablenkvor-
horizontally with constant selectable velocity from left to right. The time
gang (alternierend) erfolgen. Beide Kanäle können aber auch innerhalb
base is started by a socalled trigger signal which is derived from any
einer Zeit-Ablenkperiode mit einer hohen Frequenz ständig umgeschal-
of the available sources. The time base performs one cycle and rests
tet (chopmode) werden. Dann sind auch langsam verlaufende Vorgänge
waiting for the next trigger. It is hence immaterial when the next signal
fl immerfrei darstellbar. Für das Oszilloskopieren langsam verlaufender
arrives, the signal needs only to be repetitive, it need not be periodic!
Vorgänge mit Zeitkoeffi zienten
The time between triggers may be any, at low repetition frequencies the
triebsart meistens nicht geeignet. Das Schirmbild fl immert dann zu
display becomes darker, at very low ones the trace will not be visible
stark, oder es scheint zu springen. Für Oszillogramme mit höherer
any more. In order to achieve a stable display, the trigger must always
Folgefrequenz und entsprechend kleiner eingestellten Zeitkoeffi zienten
be derived from the very same portion of the signal. The slope and the
ist die gechoppte Art der Kanalumschaltung meist nicht sinnvoll.
level of the triggering signal can be chosen.
Liegt Additions-Betrieb (ADD) vor, werden die Signale beider Kanäle
algebraisch addiert (+CH1 ±CH2). Ob sich hierbei die Summe oder die
Note: Various trigger sources are available: the two input channels, an
Differenz der Signalspannungen ergibt, hängt von der Phasenlage
external input, a signal taken from the mains, a TV trigger. Of course,
bzw. Polung der Signale selbst und davon ab, ob eine Invertierung im
the triggering signal must be synchronous to the signal to be displa-
Oszilloskop vorgenommen wurde.
yed. The minimum amplitude for stable triggering is called the trigger
threshold. With internal triggering the trigger signal is taken off in the
two input amplifiers, the minimum amplitude here is given in mm ver-
tical deflection, independent of the positions of the VOLTS/DIV switches.
With external triggering the minimum amplitude is given in Vpp at the
external trigger input connector. The trigger amplitude may be much
larger than the threshold, but it is advisable not to exceed 20 times
the threshold.
The oscilloscope features two trigger operation modes to be de-
scribed.
6.1

Automatic peak-to-peak triggering

13
, the CH 1
Please refer to the chapter Controls for specific information about the
controls SLOPE
When using AUTOSET, this trigger mode will be automatically selected.
If DC coupling is selected, the peak-to-peak detection will be disabled,
while the function of the auto trigger will remain active. With auto trigger
selected, there will be always a trace visible, because the time base
will restart periodically if no trigger signal is present or if only a DC
voltage is applied. The auto trigger function implies that the user is only
required to operate the VOLTS/DIV and TIME/DIV controls.
The TRIGGER-LEVEL knob is active with auto peak-to-peak triggering,
its range is automatically adjusted to the peak-to-peak level measured,
sin ϕ = —
cos ϕ =
ϕ = arc sin —
500 μs/DIV ist die alternierende Be-
≤
9
, TRIGGER-LEVEL 10 , and TRIGGER
zu verb
störun
XY-Be
Das für
zeichne
"Bedie
In dies
wird m
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32 . regler
in X-Ri
der X-P
von Ka
a
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b
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( )
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2 sowoh
1 – —
b
die mit
X und Y
a
b
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Na
Sig
zah
– Ph
Phase
Eine gr
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(DUAL
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XY-Bet
Zu dies
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19
) für
knopf
16 to 23 .