Subject to change without notice
13
T
3
: alters the middle frequencies
T
4
: alters the leading edge
T
5
: alters the lower frequencies
(LF)
(LF)
One output provides
0.2V
pp
±1% (t
r
<4ns) for 10:1 probes,
and the other
2V
pp
±1% for 100:1 probes. When the
attenuator switches are set to
5mV/div
vertical deflection
coefficient, these calibration voltages correspond to a
screen amplitude of
4div
.
The output sockets have an internal diameter of 4.9mm to
accommodate the internationally accepted shielding tube
diameter of modern Modular Probes and F-series slimline
probes. Only this type of construction ensures the extremly
short ground connections which are essential for an
undistorted waveform reproduction of non-sinusoidal high
frequency signals.
Adjustment at 1kHz
The C-trimmer adjustment compensates the capacitive
loading on the oscilloscope input (approx. 20 pF for the
HM 303). By this adjustment, the capacitive division
assumes the same ratio as the ohmic voltage divider to
ensure the same division ratio for high and low frequencies,
as for DC. (For 1:1 probes or switchable probes set to 1:1,
this adjustment is neither required nor possible). A baseline
exactly parallel to the horizontal graticule lines is a major
condition for accurate probe adjustments. (See also “Trace
rotation
TR
”).
Connect the probes (Types HZ51, 52, 53, 54, or HZ36) to
the
CH.I
input. All pushbuttons should be released (in the
out position). Set input coupling to DC, the attenuator to
5 mV/div.
, and
TIME/DIV.
switch to
0.2 ms/div.
, and all
variable controls to
CAL.
position. Plug the the probe tip
into the appropriate calibrator output socket, i.e. 10:1
probes into the
0.2V
socket, 100:1 probes into the
2V
socket.
1 kHz
incorrect correct incorrect
Approximately 2 complete waveform periods are displayed
on the CRT screen. Now the compensation trimmer has to
be adjusted. Normally, this trimmer is located in the probe
head. On the 100:1 probe HZ53, however, it is located in the
connecting box at the other end of the cable. 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 4 div. ± 0.12div. (= 3 %). 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 inductances and capacitors)
which permit probe compensation in the range of the
upper frequency limit of the vertical oscilloscope amplifier.
HZ51, HZ54
Only this compensative adjustment ensures optimum
utilisation 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 HM303 can be utilized without risk of unwanted
waveform distortion.
Prerequisite for this HF compensation is a square wave
generator with fast risetime (typically 4 ns), and low
output impedance (approx. 50
Ω
), providing 0.2V and 2V at
a frequency of approx. 1MHz. The calibrator output of the
HM303 meets these requirements when the
CAL.
pushbutton is depressed.
Connect the probe to CH.I input. Depress the
CAL.
pushbutton for 1MHz. All other pushbuttons should be
released (out position). Set the CH.I input coupling to
DC
,
attenuator switch to
5mV/div
, and TIME/DIV. switch to
0.2µs/div.
Set all variable controls to
CAL
. position.
Insert the probe tip into the output socket marked
0.2V
.
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 connecting boxes of the HZ51 and
HZ54 contain one R-trimmer screw each, while that of the
HZ52 provides three. These R-trimmers have to be adjusted
such that the beginning of the pulse is as straight as
possible. Overshoot or excessive rounding are unaccept-
able. This is relatively easy on the HZ51 and HZ54, but
slightly more difficult on the HZ52. The rising edge should
be as steep as possible, with a pulse top remaining as
straight and horizontal as possible.
On the HZ52, each of the three trimmers has a clearly
defined area of influence on the waveform shape (see
Fig.), offering the added advantage of being able to
straighten out waveform abberations near the leading
edge.
