Mhz Adjustment; Operating Modes Of The Vertical Amplifi Er; Xy Mode - Hameg HM400 Handbuch

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
probe manual for its location) until the square wave is perfectly fl at, i.e
there are neither under- nor overshoots. The transitions are invisible at
this sweep speed (see the pictures). The amplitude of the square wave
should be within 4 ±0.12 DIV.
undershoot correct

1 MHz adjustment

The probes supplied with the scope have additional adjustment ele-
ments which allow to correct for aberrations at high frequencies.
After this adjustment maximum bandwidth and best pulse response of
the combination scope and probe are obtained by achieving maximally
fl at group delay; overshoots, undershoots, ripple are minimized.
This adjustment requires a fast square wave generator (
output impedance (50 ohms) which delivers 0.2 Vpp at 1 MHz; the PROBE
ADJUST output of the scope fulfi lls these requirements.
Connect the 10:1 probe to the input to be used. Select PROBE ADJUST
signal 1 MHz with the knob „TIME/DIV (see the chapter Controls) switch
the coupling to DC, the VOLTS/DIV selector to 5 mV/DIV and the TIME/DIV
selector to 100 ns/DIV. Connect the probe tip and ground to the two
PROBE ADJUST contacts. The square wave will now be visible and also
its rising and falling slopes. See the probe manual for the location of
the adjustment elements.
Adjustment criteria:
Only the rising slope and the top of the square wave are of concern,
disregard the other portions of the signal.
– Short rise time
– Clean transition from the rising slope to the top of the square
wave with no over- or undershoot, fl at top.
undershoot correct
The amplitude of the square wave should be identical to that with the
1 kHz signal. It is important to always fi rst perform the 1 kHz adjustment,
in general a readjustment of the 1 kHz will not be necessary. Please
note that the probe adjust frequencies are not precise and hence must
not be used for any checks of the accuracy of the time base, also their
duty cycle is not controlled.
The probe adjust signal must conform to the requirements of zero
potential at the bottom of the square wave, precise amplitude and fl at
tops; its frequencies and duty cycles need not be precise.
34 Subject to change without notice
Operating modes of the vertical amplifi er
The most important controls determining the operating modes of the
vertical amplifer are the mode buttons CH 1
ADD 44 and XY
Changing the modes is described in the chapter Controls. Yt is by far
the mode most used: the input signal defl ects the trace vertically while
a time base moves the trace from left to right. The Y amplifi er offers
overshoot
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
< 5 ns) and low is unsuited at slow time bases because the alternation becomes visible
with disturbing fl icker, here, the chopped mode will yield a fl icker-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 amplifi er! 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 mo-
derate, and the common mode range is limited to the normal operating
range of the input amplifi ers. 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.
overshoot

XY mode

For this mode use the button XY
45
under .
In this mode the time base is disabled. The CH1 input signal will defl ect
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 magnifi er is also disabled. When using
this mode, the low bandwidth of the X amplifi er (see the specifi cations)
has to be observed, the phase difference between the wide band vertical
amplifi er and the X amplifi er increases with frequency.
The Y signal may be inverted by pressing the button INV
CH 2.
Using Lissajous patterns it is possible
– STOP 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
41
45 .
45
as described in the chapter Controls
42 43
, CH 2 , DUAL ,
17
, the CH 1