31
Subject to change without notice
Operating modes of the vertical amplifiers in Yt mode
Connect the 10:1 probe to the input of the channel it is to be adjusted
for and don‘t mix up the probes later (always use that particular probe
with the same channel). Set the deflection coefficient to 5mV/div
and the input coupling to DC. The time deflection coefficient should
be set to 0.2ms/div. All deflection coefficients should be calibrated
(Variable controls at CAL position). Plug the probe tip into the calibrator
output socket. Approximately 2 complete waveform periods are
displayed on the CRT screen. The compensation trimmer should be
adjusted. The location of the low frequency compensation trimmer
can be found in the probe information sheet. Adjust the trimmer
with the insulated screwdriver provided, until the tops of the square
wave signal are exactly parallel to the horizontal graticule lines (see
1kHz diagram). The signal height should then be 4div ± 0.16div (= 4
% (oscilloscope 3% and probe 1%). During this adjustment, the
signal edges will remain invisible.
Adjustment at 1MHz
Probes
HZ51
,
52
and
54
can also be HF compensated. They
incorporate resonance de-emphasing networks (R-trimmer in
conjunction with capacitor) which permit probe compensation in
the range of the upper frequency limit of the Y amplifier. Only this
compensation adjustment ensures optimum utilization of the
full bandwidth, together with constant group delay at the high
frequency end, thereby reducing characteristic transient distortion
near the leading edge (e.g. overshoot, rounding, ringing, holes or
bumps) to an absolute minimum.
Using the probes
HZ51, 52
and
54
, the full bandwidth of the
oscilloscope can be utilized without risk of unwanted
waveform distortion.
Prerequisite for this HF compensation is a square wave
generator with fast risetime (typically 4ns), and low output
impedance (approx. 50 Ohm), providing 0.2V at a frequency of
approx. 1MHz. The calibrator output of this instrument meets
these requirements.
Connect the probe to the input previously used when 1kHz
adjustment was made. Select 1MHz output frequency. Operate
the oscilloscope as described under 1kHz but select for 0.2µs/
div time deflection coefficient setting.
Insert the probe tip into the output socket. A waveform will be
displayed on the CRT screen, with leading and trailing edges clearly
visible. For the HF-adjustment now to be performed, it will be
necessary to observe the rising edge as well as the upper left
corner of the pulse top. The location of the high frequency
compensation trimmer(s) can also be found in the probe information
sheet. These R-trimmer(s) have to be adjusted such that the
beginning of the pulse is as straight as possible. Overshoot or
excessive rounding is unacceptable. The adjustment is relatively
easy if only one adjusting point is present. In case of several adjusting
points the adjustment is slightly more difficult, but causes a better
result. The rising edge should be as steep as possible, with a pulse
top remaining as straight and horizontal as possible.
After completion of the HF adjustment, the signal amplitude
displayed on the CRT screen should have the same value as
during the 1kHz adjustment.
Probes other than those mentioned above, normally have a larger
tip diameter and may not fit into the calibrator output. Whilst it is
not difficult for an experienced operator to build a suitable adapter,
it should be pointed out that most of these probes have a slower
risetime with the effect that the total bandwidth of scope together
with probe may fall far below that of the oscilloscope. Furthermore,
the HF adjustment feature is nearly always missing so that
waveform distortion can not be entirely excluded. The adjustment
sequence must be followed in the order described, i.e. first at
1kHz, then at 1MHz.
Prerequisites for precise and easy probe adjustments, as well
as checks of deflection coefficients, are straight horizontal pulse
tops, calibrated pulse amplitude, and zero-potential at the pulse
base. Frequency and duty cycle are relatively uncritical. For
interpretation of transient response, fast pulse risetimes and
low impedance generator outputs are of particular importance.
Providing these essential features, as well as selectable output
frequencies, the calibrator of the instrument can, under certain
conditions, replace expensive squarewave generators when
testing or compensating wideband attenuators or amplifiers.
In such a case, the input to an appropriate circuit will be
connected to the calibrator output via a suitable probe.
The voltage provided by the probe to a high impedance input
(1M Ohm II 15-30pF) will correspond to the division ratio of the
probe used (10:1 = 20mVpp output). Suitable probes are
HZ51
,
52
, and
54
.
Operating modes of the Y amplifiers in Yt mode.
The most important controls regarding the operating modes
of the Y amplifiers are the pushbuttons:
CHI (15), DUAL (16)
and
CH II (19)
. Their functions are described in the section
”Controls and Readout”.
In most cases oscilloscopes are used to display signals in Yt
mode. Then the signal amplitude deflects the beam in vertical
direction while the time base causes an X deflection (from left
to right) at the same time. Thereafter the beam becomes
blanked and fly back occurs.
The following Yt operation modes are available:
Single channel operation of channel I (Mono CH I).
Single channel operation of channel II (Mono CH II).
Two channel operation of channel I and channel II (DUAL).
Two channel operation of channel I and channel II displaying
the algebraic result as the sum or difference (“add”).
The way the channel switching is determined in
DUAL
mode
depends on the time base setting and is described in the
section ”Controls and Readout”.
In
ADD
mode the signals of both channels are algebraically added
and displayed as one signal. Whether the resulting display shows
the sum or difference is dependent on the phase relationship or
the polarity of the signals and on the invert function.
In
ADD
mode the following combinations are possible for
In phase input voltages:
Channel II invert function inactive = sum.
Channel II invert function active = difference.
Antiphase input voltages:
Channel II invert function inactive = difference.
Channel II invert function active = sum.
In the
ADD
mode the vertical display position is dependent
upon the
Y
position setting of both channels. The same Y
deflection coefficient is normally used for both channels with
algebraic addition.
