Hameg HM504-2, Manual

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Subject to change without notice
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The automatic peak (value) triggering operates over all variations
or fluctuations of the test signal above 20 Hz. However, if the
pulse duty factor of a square wave signal exceeds a ratio of
100 : 1, switching over to normal triggering will be necessary.
Automatic triggering is practicable with internal and external
trigger voltage.
Normal Triggering
Information specific to the instrument is given in the sections NM
- AT - [9], LEVEL [11] and TRIG. MODE [20] in the paragraphs
”Controls and Readout”. The time fine adjustment (VAR.), and
the holdoff time setting assist in triggering under specially difficult
signal conditions.
With normal triggering, the sweep can be started by AC signals
within the frequency range defined by the trigger coupling setting.
In the absence of an adequate trigger signal or when the trigger
controls (particularly the trigger
LEVEL control) are misadjusted,
no trace is visible.
When using the internal normal triggering mode, it is possible to
trigger at any amplitude point of a signal edge, even with very
complex signal shapes, by adjusting the trigger
LEVEL control. If
the signal applied at the Y input is used for triggering (internal
trigger source), its adjusting range is directly dependent on the
display height, which should be at least 0.5div. If it is smaller than
1div, the trigger
LEVEL adjustment needs to be operated with a
sensitive touch. In the external normal triggering mode, the same
applies to approx. 0.3 V
pp
external trigger voltage amplitude.
Other measures for triggering of very complex signals are the use
of the time base variable control and
HOLDOFF time control,
mentioned below.
SLOPE
Please note item [9] in section ”Controls and Readout” for
instrument specific information.
The actual slope setting is displayed in the readout. The setting
is not changed by the
AUTO SET function. The slope setting can
be changed for the delay time base trigger unit in delay mode if
the delay trigger function is active. The previous slope setting for
the undelayed time base trigger is stored and still active. For
further information please note ”Controls and Readout”.
The time base generator can be triggered by a rising or falling
edge of the test signal. Whether the rising or the falling edge is
used for triggering, depends on the slope direction setting. This
is valid with automatic and normal triggering. The positive slope
direction means an edge going from a negative potential and
rising to a positive potential. This has nothing to do with zero or
ground potential or absolute voltage values. The positive slope
may also lie in a negative part of a signal.
However the trigger point may be varied within certain limits on
the chosen edge using the
LEVEL control. The slope direction is
always related to the input signal and the non inverted display.
Trigger coupling
Instrument specific information regarding this item can be noted
in the ”Data Sheet”. The coupling setting
TRIG. MODE [20] and
indication are described under ”Controls and Readout”.
As the automatic triggering does not work below 20 Hz, normal
triggering should be used in DC and LF trigger coupling mode. The
coupling mode and accordingly the frequency range of the trigger
signal should meet the signal requirements.
AC: This is the most frequently used trigger mode. The trigger
threshold increases below and above the frequency limits
mentioned in the data sheet. This filter cuts off both the DC
content of the trigger signal and the lowest frequency range.
DC: In this coupling mode the trigger signal is coupled galvanically
to the trigger unit if normal triggering (NM) is present.
Therefore there is no low frequency limit.
DC triggering is recommended if the signal is to be triggered
with quite slow processes or if pulse signals with constantly
changing pulse duty factors have to be displayed.
HF: In this coupling mode the transmission range equals a high
pass filter. It cuts off the DC content of the trigger signal and
the lower frequency range.
LF: LF trigger coupling has a low pass filter function characteristic.
As in DC trigger coupling, there is no limit for the pass
frequency range in connection with normal triggering.
The LF trigger coupling is often more suitable for low frequency
signals than DC trigger coupling because the noise
components of the trigger signals are strongly suppressed.
This avoids or reduces, under borderline conditions, jitter or
double traces especially with very low signal voltages. The
trigger threshold rises continuously above the pass band.
TVL: The built in active TV Sync Separator provides the separation
of line sync pulses from the video signal.
Even distorted video signals are triggered and displayed in a
stable manner. This mode is described under paragraph
”Triggering of video signals”.
TVF: The built in active TV Sync Separator also provides the
separation of frame sync pulses from the video signal. Even
distorted video signals are triggered and displayed in a stable
manner.
This mode is described under paragraph ”Triggering
of video signals”.
~: Indicates “line/mains triggering” and is described under the
paragraph of the same name.
Triggering of video signals
In TVL and TVF trigger coupling mode the instrument is
automatically set to automatic triggering and the trigger point
indicator is switched off. As only the separated synchronization
pulses are used for triggering the relationship between the
displayed signal and the trigger signal is lost. In
TVF mode
interference may occur if chopped DUAL mode is chosen or the
readout is active.
Video signals are triggered in the automatic mode. The internal
triggering is virtually independent of the display height, but the
sync pulse must exceed 0.5div height.
The polarity of the synchronization pulse is critical for the slope
selection. If the displayed sync pulses are above the picture (field)
contents (leading edge positive going), then the slope setting for
Triggering and time base