Hameg HM504-2, Manual

Page: 34 / 42

Subject to change without notice
32
The manipulation of time delay requires a certain experience,
especially with complicated signal combinations which are
difficult to display. The display of sections of simple signals is, in
contrast, fairly easy. The time delayed display is also possible in
the dual channel, addition and difference modes.
In chopped DUAL mode, if after switching over to “del” or “dTr”,
the time deflection coefficient is reduced (TIME/DIV.), the channel
switching mode doesn`t change automatically to alternate.
Attention:
In chopped DUAL mode, using high expansion ratios in “del”
mode, chop interference may be visible. This can be overcome
by selecting alternate DUAL mode. A similar effect can be
caused by the READOUT with the result that parts of a signal
displayed in CH I, CH II or DUAL mode are blanked
(unsynchronised). In such a case the READOUT can be
switched off.
AUTOSET
The instrument specific information regarding this function is part
of the section ”Controls and Readout” paragraph
AUTOSET [2] .
As also mentioned in that section, all controls are electronically
selected with the exception of the
POWER pushbutton.
Thus automatic, signal related instrument set up in Yt (time base)
mode is possible. In most cases no additional manual instrument
setting is required.
Briefly pressing the AUTOSET pushbutton causes the instrument
to switch over to the last Yt mode settings regarding CH I , CH II
and DUAL . If the instrument was operated in Yt mode, the actual
setting will not be affected with the exception of ADD mode
which will be switched off. At the same time the attenuator(s)
(
VOLTS/DIV ) are automatically set for a signal display height of
approx. 6 div in mono channel mode or if in DUAL mode for
approx. 4 div height for each channel. In the determination of the
time deflection coefficient, it is assumed that the pulse duty
factor of the input signal is approx. 1:1.
The time deflection coefficient is also set automatically for a
display of approx. 2 signal periods. The time base setting occurs
randomly if complex signals consisting several frequencies e.g.
video signals are present. If cursor voltage measurement is
selected, AUTOSET also affects the position of the CURSOR
lines.
Please note AUTOSET [2] in section ”Controls and
Readout”.
AUTOSET sets the instrument automatically to the following
operating conditions:
I
AC or DC input coupling unaltered
or in GND condition the last used setting
I
Internal triggering (channel I or channel II)
I
Automatic triggering
I
Trigger level in electrical midrange position
I
Optimum calibrated Y deflection coefficient(s) 5 mV - 20 mv/div
I
Optimum calibrated Time base deflection coefficient
I
AC trigger coupling (except if DC trigger coupling last present
I
Undelayed time base mode
I
X x10 magnifier switched off
I
Optimum X and Y position settings
I
Trace and readout visible.
If DC trigger coupling had been selected, AC trigger coupling will
not be chosen and the automatic trigger is operative without the
peak value detection.
The X position is set to the CRT centre as well as the Y position
in CH I or CH II mode. In DUAL mode the channel I trace is set to
the upper half and the channel II trace to the lower half of the CRT.
The 1 mV/div and 2 mV/div deflection coefficient will not be
selected by
AUTOSET as the bandwidth is reduced on these
settings.
Attention!
If a signal is applied with a pulse duty factor of approx. 400 :1
or larger, an automatic signal display can not be performed.
The pulse duty factor causes too low a Y deflection coefficient
(sensitivity too high) and too high a time deflection coefficient
(time base speed to slow) and results in a display in which
only the baseline is visible.
In such cases it is recommended to select normal triggering and
to set the trigger point approx. 0.5div above or below the trace.
If under one of these conditions the trigger indicator LED is lit, this
indicates the presence of a signal. Then both the time coefficient
and Y deflection coefficient should be reduced. Please note that
a reduction in intensity may occur, which could result in a blank
screen when the physical limits are reached.
Mean Value Display
The DC Mean Value is displayed in place of the cursor line
measurement, if the cursor lines are switched off, the AUTO
MEASURE menu function “DC” is activated and further condition
are met:
The signal to be measured (AC > 20 Hz) must be applied at input
CH I
[25] or CH II [28] with its DC content at the measuring
amplifier; DC input coupling [26; 29] required. Yt (time base) mode
in combination with internal triggering (trigger source CH I or
CH II; not alternated triggering) must be present. AC or DC trigger
coupling must be selected.
If the above conditions are not met, ”n/a” will be displayed.
The mean value is acquired using the trigger signal amplifiers
used for internal triggering. With the exception of DUAL mode,
the indicated mean value is automatically related to the active
channel (CH I or CH II), as the channel selection also assigns the
trigger amplifier. In DUAL mode one can select between trigger
amplifier CH I or CH II for triggering. The indicated mean value
refers to the channel from which the trigger signal originates.
The DC mean value is displayed with an algebraic sign (e.g.
”dc:Y1 501mV” resp. ”dc:Y1 -501mV). Overranging is indicated
by ” < ” resp. ” > ” sign (e.g. ”dc:Y1 <1.80V” resp. ”dc:Y1
>1.80V”). Being dependent on a necessary time constant for
mean value creation, the display update requires a few seconds
after a voltage change.
The reading accuracy is dependent on the instrument
specifications (Y deflection tolerance max. 3% from 5 mV/div. to
20 V/div.). Although the tolerances are significantly smaller in
AUTOSET