Operating Modes Of The Vertical Amplifier; Xy Mode; Measurement Of Phase Differences In Dual Channel Operation; Triggering And Time Base - Hameg Instruments HM 400 Manuel

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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

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

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

, 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-

≤

, TRIGGER-LEVEL

, and TRIGGER

zu verb

störun

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Das für

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der X-P

von Ka

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Eine gr

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(DUAL

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Zu dies

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knopf

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