Measurement Of Phase Differences In Dual Channel Operation; Triggering And Time Base; Automatic Peak-To-Peak Triggering; Normal Trigger - Hameg HM400 Handbuch

– to measure the phase difference between two signals of the same
frequency.
Measurement of phase differences in dual channel
operation
A much more precise and convenient method of measuring phase
differences which is also applicable up to high frequencies is the
measurement of the time difference in dual channel operation. Please
note: 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. Another advantage of this me-
thod is the fact that the time difference
is still measurable even if the signals
are corrupted by hum, ripple or noise.
Also, there are no ambiguities. Alterna-
tively Lissajous patterns can be used for
measurement of phase differences.

Triggering and time base

The pertinent controls are located to the right of the VOLTS/DIV knobs,
see the chapter Controls.
In Yt operation the signal defl ects the trace vertically while it is defl ected
horizontally with constant selectable velocity from left to right. The time
base is started by a socalled trigger signal which is derived from any
of the available sources. The time base performs one cycle and rests
waiting for the next trigger. It is hence immaterial when the next signal
arrives, the signal needs only to be repetitive, it need not be periodic!
The time between triggers may be any, at low repetition frequencies the
display becomes darker, at very low ones the trace will not be visible
any more. In order to achieve a stable display, the trigger must always
be derived from the very same portion of the signal. The slope and the
level of the triggering signal can be chosen.
Note: Various trigger sources are available: the two input channels, an
external input, a signal taken from the mains, a TV trigger. Of course, the
triggering signal must be synchronous to the signal to be displayed. The
minimum amplitude for stable triggering is called the trigger threshold.
With internal triggering the trigger signal is taken off in the two input
amplifi ers, the minimum amplitude here is given in mm vertical defl ec-
tion, 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 descri-
bed.

Automatic peak-to-peak triggering

Please refer to the chapter Controls for specifi c information about the
13
controls SLOPE , TRIGGER-LEVEL
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
a
sin ϕ = —
b
a
2
( )
cos ϕ =
1 – —
b
a
ϕ = arc sin —
b
14 23 28
, and TRIGGER to .
T r i g g e r i n g a n d t i m e b a s e
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,
it becomes hence independent of the amplitude and the shape of the
signal. The duty cycle may e.g. vary from 1 : 1 to 1 : 100 without loss of the
trigger. It may, however, be sometimes necessary to set the TRIGGER-
LEVEL control close to one of its extremes. The next measurement may
require another setting. The simplicity of operation recommends the
auto peak-to-peak triggering for most uncomplicated measurements. It
is also a good start with diffi cult problems, especially, if the properties
of a signal like amplitude, frequency and shape are unknown.
The auto peak-to-peak trigger mode is independent of the trigger source
and operates above 5 Hz, i.e., if the repetition frequency of the triggering
signal is lower, the time base will freerun.

Normal trigger

In this mode all settings are up to the user, and there is no visible trace if
there is no suffi cient trigger signal. See the chapter Controls for specifi c
information about the functions of the controls SLOPE
LEVEL 14 , and TRIGGER 23 to
additional use of the functions Time Base Variable (VAR) and HOLD-OFF
time adjustment.
In the normal trigger mode the trigger signal can be
derived from any portion of the rising or falling slopes of
the signal by proper setting of the TRIGGER-LEVEL knob.
The available trigger range depends on the amplitude of
STOP the signal.
If the signal amplitude on the screen is
the adjustment may become critical due to the small range available
and require some care. As mentioned there will be no visible trace if
the TRIGGER-LEVEL setting is false or if the trigger signal is missing
or insuffi cient. The normal trigger mode allows to also trigger on
complicated signals. With mixed signals it is, however, necessary that
repetitive signal peaks are present which can be caught by careful
operation of the TRIGGER-LEVEL control.

SLOPE selection

13
With the SLOPE button the signal slope is selected, see the chapter
Controls. This selection is always valid, also in AUTOSET mode. A rising
slope is defi ned as a portion of a signal which rises from a given potential
to a more positive one, a falling slope correspondingly is defi ned as a
down slope from a given potential to a more negative one.

Trigger coupling

See the chapter Controls for specifi c information about the controls
13 14
SLOPE , TRIGGER-LEVEL
of trigger coupling AC or DC remains unaffected by AUTOSET. See
the specifi cations for the passbands of the various modes of trigger
coupling. With DC or LF coupling use the normal trigger mode and the
TRIGGER-LEVEL knob. These modes are available:
AC: This is the standard coupling mode. It has a low and a high frequency
limit, below resp. above these limits the trigger threshold rises.
DC: DC coupling is effective from DC to the upper frequency limit. This
mode is recommended for slowly varying signals when triggering
on a defi nite portion is desired or when the duty cycle of signals
varies.
LF: When LF is selected, a low pass fi lter is inserted in the trigger path.
In combination with the normal trigger mode there is no lower
13
, TRIGGER-
28 . Complex signals may require the
< 1 DIV with internal triggering,
23 28
, and TRIGGER to . The selection
Subject to change without notice
35