Hameg Instruments HM 203-6 Bedienungsanleitung Seite 12

clockwise and back to the calibrated detent CAL. If the trace
moves from the vertical position (up or down) more than
1mm, the DC balance will require readjustment. This check
should be made after a 20 minute warm-up period.
Adjustment procedure ne
The following instructions should be performed to obtain
the correct DC balance adjustment of both channels.
— Remove all input cables and adjust oscilloscope controls
to display the baseline.
— Center the baseline using Y-POS. and X-POS. controls.
— Set attenuator switches to 5mV/em and input coupling
switches to GD.
— Release all pushbuttons in the Y-field.
— Place the oscilloscope so that it rests firmly on its back (up-
right position) and locate DC balance adjustment poten-
tiometer access holes — marked CH.] DC-BALANCE
CH.I — which are found underneath the instrument.
— Insert a screwdriver (blade approx. 3mm, length min.
20mm} in CH.I hole. A plastic guide with slotted bottom
is located behind the hole.
— Rotate VOLTS/DIV. variable control to and fro and
adjust balance pot so that the baseline no longer moves
up or down. When the trace remains steady, correction
of CH.I is completed.
— Depress CHI/H button. Repeat adjustment procedure
for CH.IL.
Probe compensation and use
The attenuator probe must be matched exactly to the input
impedance of the vertical amplifier to ensure an undistorted
display of waveforms. A generator built into the HM 203-6
supplies a square wave signal for this purpose with very
short rise time (<5 ns) at 1 kHz. The square wave signal can
be taken from the two eyelets beneath the screen. One out-
put supplies 0.2V,, £1% for x10 attenuator probes, the
other 2V,, £1% for x100 attenuator probes. These volt-
ages correspond In each case to a screen amplitude of 4em
provided the input attenuator switch of the HM 203-6 is set
to the deflection coefficient 5 mV/cem.
1 kHz compensation |
This trimmer adjustment compensates the capacitive load-
ing of the oscilloscope input (approx. 30 pF for the HM 203-6).
After compensation, the capacitive attenuation has the
same attenuation ratio as the ohmic divider. The same volt-
age attenuation then results at high and low frequencies as
for direct voltage (for x1 probes or probes switches over to
x1, this compensation is neither necessary nor possible).
The trace line must be parallel with the horizontal graticule
lines (see "Trace rotation TR", page M7).
Connect attenuator probe (type HZ 51, 52, 53, 54 or also HZ
36 and HZ 37) to the CH.I input, do not press any buttons or
turn any knobs, set input coupling to DC, input attenuator to
5 mV/cem and TIME/DIV. switch to 0.2 ms/em (both vari-
able controls in calibration position CAL.), connect probe to
the corresponding CAL. eyelet (x10 probe to 0.2 V eyelet,
x100 to 2 V eyelet).
1 kHz
incorrect
incorrect correct
2 cycles can be seen on the screen. The compensation trim-
mer must now be adjusted. It is generally located in the
probe Itself. It is located in the x100 attenuator probe HZ53
in the small box on the BNC plug. Adjust the trimmer with
the insulating screw driver provided until the tops of the
Square wave signal are exactly parallel to the horizontal
graticule lines (see 1 kHz diagram). The signal height should
then be 4cm £1.2 mm (= 3 %). The signal edges are invis-
ible during this adjustment.
1 MHz compensation
HF adjustment is possible for the HZ37, 51, 52, and 54
probes. These possess resonance correction elements
(pots in combination with coils and capacitors) with which it
is possible for the first time to simply adjust the probe in the
upper frequency range of the vertical amplifier.
After this compensation, not only the maximum possible
bandwidth ts obtained in the attenuator probe mode but
also a largely constant group delay at the end of the
bandwidth. In this way transient distortions (such as over-
shooting, rounding off, ringing, holes or humps in the pulse
top) in the vicinity of the leading edge are kept to a
minimum. The bandwidth of the HM 203-6 is therefore fully
utilized when using the HZ37, 51, 52 and 54 probes without
having to accept wave form distortions.
Prerequisite for this HF compensation is a square wave
generator with short rise time (typically 4 ns) and low-
impedance output (approx. 50 Ohm) which also supplies a
voltage of 0.25 V or 2.5 V at a frequency of 1 MHz.
The Scope Tester HZ60 faulifilis these tasks excellently
(see Accessories, page 21).
M8 203-6
Subject to change without notice