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connection is made between the 0.2V output and the input
of the vertical amplifier (e.g. using a
x1 probe),
the displayed
signal in the 50mV/div. position (variable control to CAL.)
should be
4div.
high (DC input coupling). Maximum devia¬
tions of 0.12div. (3 %) are permissible. If a x
10probe
is con¬
nected between the 2 V output and Y input, the same display
height should result. With higher tolerances it should first be
investigated whether the cause lies, within the amplifier or in
the amplitude of the square-wave signal. On occasions it is
possible that the probe is faulty or incorrectly compensated.
If necessary the measuring amplifier can be calibrated with
an accurately known DC voltage (DC input coupling). The
trace position should then vary in accordance with the deflec¬
tion coefficient set.
With variable control at the attenuator switch fully conter-
clockwise, the input sensitivity is decreased at least by the
factor 2.5 in each position. In the 50mV/div. position, the
displayed calibrator signal height should vary from 4div. to at
least 1.6div.
Transmission Performance of the
Vertical Amplifier
The transient response and the delay distortion correction
can only be checked with the aid of a square-wave generator
with a fast risetime
{max. 5ns).
The signal coaxial cable (e.g.
HZ34) must be terminated at the vertical input of the oscillo¬
scope with a resistor equal to the characteristic impedance
of the cable (e.g. with HZ22). Checks should be made at
100Hz, 1kHz, 10kHz, 100kHz and 1MHz, the deflection
coefficient should be set at 5 mV/div. with DC input coupling
(Y variable control in CAL. position). In so doing, the square
pulses must have a flat top without ramp-off, spikes and
glitches; no overshoot is permitted, especially at 1 MHz and
a display height of
4-5div..
At the same time, the leading top
corner of the pulse must not be rounded. In general, no great
changes occur after the instrument has left the factory, and
it is left to the operator's discretion whether this test is
undertaken or not. A suited generator for this test is HZ60
from HAMEG.
Of course, the quality of the transmission performance is not
only dependent on the vertical amplifier.
The input
attenuators,
located in the front of the amplifier,
are fre¬
quency-compensated in each position.
Even small capaci¬
tive changes can reduce the transmission performance.
Faults of this kind are as a rule most easily detected with a
square-wave signal with a low repetition rate (e.g. 1 kHz). If a
suitable generator with max. output of 40Vpp is available, it is
advisable to check at regular intervals the deflection coeffi¬
cients on all positions of the input attenuators and readjust
them as necessary. A compensated
2:1 series attenuator
(e.g. HZ23) is also necessary, and this must be matched to
the input impedance of the oscilloscope. This attenuator
can be made up locally. It is important that this attenuator is
shielded. For local manufacture, the electrical components
required are a 1 MQ ±1 % resistor and, in parallel with it, a
trimmer 3-15 pF in parallel with approx. 20 pF. One side of
this parallel circuit is connected directly to the input connec¬
tor of CH. I or CH. II and the other side is connected to the
generator, if possible via a low-capacitance coaxial cable.
The series attenuator must be matched to the input imped¬
ance of the oscilloscope in the 5mV/div. position (variable
control to CAL., DC input coupling; square tops exactly hori¬
zontal; no ramp-off is permitted). This is achieved by adjust¬
ing the trimmer located in the 2:1 attenuator.
Theshapeof
the square-wave shouid then be the same in each input
attenuator position.
Operating Modes: CH.I/II, DUAL, ADD,
CHOP., INVERT and X-Y Operation
On depressing the DUAL pushbutton, two traces must
appear immediately. On actuation of the Y-POS. controls,
the trace positions should have no effect on each other.
Nevertheless, this cannot be entirely avoided, even in fully
serviceable instruments. When one trace is shifted verti¬
cally across the entire screen, the position of the other trace
must not vary by more than 0.5mm.
A criterion in chopped operation is trace widening and
shadowing around and within the two traces in the upper or
lower region of the screen. Set TIME/DIV. switch to 2[xs/
div., depress the DUAL and CHOP, pushbutton, set input
coupling of both channels to GD and advance the INTENS.
control fully clockwise. Adjust FOCUS for a sharp display.
With the Y-POS. controls shift one of the traces to a -(- 2 div.,
the other to a -2div. vertical position from the horizontal
center line of the graticule. Do not try to synchronize (with
the time variable control) the chop frequency (0.4MHz)!
Then alternately release and depress the CHOP, pushbut¬
ton. Check for negligible trace widening and periodic
shadowing in the chopped mode.
It is important to note that in the IH-II add mode (only ADD
depressed) or the I—II difference mode (INV. CHII button
depressed in addition) the vertical position of the trace can
be adjusted by using
both
the Channel I and Channel II Y-
POS. controls.
In X-Y Operation (X-Y pushbutton depressed), the sensitiv¬
ity in both deflection directions will be the same. When the
signal from the built-in square-wave generator is applied to
the input of Channel II, then, as with Channel I in the vertical
direction, there must be a horizontal deflection of
4div.
when the deflection coefficient is set to 50mV/div. posi¬
tion (variable control set to its CAL. position, X-MAG. xIO
button in out position). The check of the mono channel dis¬
play with the CHI/II button is unnecessary; it is contained
indirectly in the tests above stated.
T2 203-7
Subject to change without notice
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