11
Subject to change without notice
They should be as short and thick as possible. When the
attenuator probe is connected to a BNC-socket, a BNC-
adapter, should be used. In this way ground and matching
problems are eliminated. Hum or interference appearing in
the measuring circuit (especially when a small deflection
coefficient is used) is possibly caused by multiple grounding
because equalizing currents can flow in the shielding of the
test cables (voltage drop between the protective conductor
connections, caused by external equipment connected to the
mains/line, e.g. signal generators with interference protection
capacitors).
Controls and Readout
The following description assumes that the operating
mode ”COMPONENT TEST” is switched off.
All important measuring parameter settings are display-
ed in the screen Readout when the oscilloscope is on.
The LED indicators on the large front panel facilitate operation
and provide additional information. Electrical end positions of
controls are indicated by acoustic signal (beep).
All controls, except the power switch (
POWER
), the calibration
frequency pushbutton (
CAL. 1kHz/1MHz
), the
FOCUS
control
and the trace rotation control, are electronically set and
interrogated. Thus, all electronically set functions and their
current settings can be stored and also remotely controlled.
The large front panel is, as is usual with Hameg oscilloscopes,
marked with several fields.
The following controls and LED indicators are located
on the top, to the right of the screen, above the horizon-
tal line:
(1) POWER
Pushbutton and symbols for
ON (I)
and
OFF (O)
.
After the oscilloscope is switched on, all LEDs are lit and
an automated instrument test is performed. During this
time the
HAMEG
logo and the software version are
displayed on the screen. After the internal test is
completed succesfully, the overlay is switched off and
the normal operation mode is present. Then the last used
settings become activated and one LED indicates the
ON condition.
(2) AUTO SET
Briefly depressing this pushbutton results in an automatic
instrument setting automatically selecting Yt mode. The
instrument is set to the last used Yt mode setting (
CH I,
CH II
or
DUAL). SEARCH (SEA)
and
DELAY (DEL
and
DTR)
mode is automatically switched off.
Please note
”AUTO SET”
.
Automatic
CURSOR
supported voltage measurement:
If
CURSOR
voltage measurement is present, the CURSOR
lines are automatically set to the positive and negative
peak value of the signal. The accuracy of this function
decreases with higher frequencies and is also influenced
Controls and Readout
When using a 50
Ω
cable such as the
HZ34
, a 50
Ω
through
termination type
HZ22
is available from
HAMEG
. When
transmitting square signals with short rise times, transient
phenomena on the edges and top of the signal may become
visible if the correct termination is not used. A terminating
resistance is sometimes recommended with sine signals as
well. Certain amplifiers, generators or their attenuators maintain
the nominal output voltage independent of frequency only if
their connection cable is terminated with the prescribed
resistance. Here it must be noted that the terminating resistor
HZ22
will only dissipate a maximum of 2Watts. This power is
reached with 10Vrms or at 28.3Vpp with sine signal. If a x10
or x100 attenuator probe is used, no termination is necessary.
In this case, the connecting cable is matched directly to the high
impedance input of the oscilloscope. When using attenuators
probes, even high internal impedance sources are only slightly
loaded (approx. 10M
Ω
II 12pF or 100M
Ω
II 5pF with
HZ53
).
Therefore, if the voltage loss due to the attenuation of the
probe can be compensated by a higher amplitude setting, the
probe should always be used. The series impedance of the
probe provides a certain amount of protection for the input of
the vertical amplifier. Because of their separate manufacture,
all attenuator probes are only partially compensated, therefore
accurate compensation must be performed on the oscilloscope
(see Probe compensation ).
Standard attenuator probes on the oscilloscope normally
reduce its bandwidth and increase the rise time. In all cases
where the oscilloscope bandwidth must be fully utilized (e.g.
for pulses with steep edges) we strongly advise using the
probes
HZ51
(x10)
HZ52
(x10 HF) and
HZ54
(x1 and x10). This
can save the purchase of an oscilloscope with larger bandwidth.
The probes mentioned have a HF-calibration in addition to low
frequency calibration adjustment. Thus a group delay correction
to the upper limit frequency of the oscilloscope is possible
with the aid of an 1MHz calibrator, e.g.
HZ60
.
In fact the bandwidth and rise time of the oscilloscope are not
noticably changed with these probe types and the waveform
reproduction fidelity can even be improved because the probe
can be matched to the oscilloscopes individual pulse response.
If a x10 or x100 attenuator probe is used, DC input
coupling must always be used at voltages above 400V.
With AC coupling of low frequency signals, the attenu-
ation is no longer independent of frequency, pulses
can show pulse tilts. Direct voltages are suppressed
but load the oscilloscope input coupling capacitor
concerned. Its voltage rating is max. 400 V (DC + peak
AC). DC input coupling is therefore of quite special
importance with a x100 attenuation probe which usu-
ally has a voltage rating of max. 1200 V (DC + peak AC).
A capacitor of corresponding capacitance and voltage
rating may be connected in series with the attenuator
probe input for blocking DC voltage (e.g. for hum
voltage measurement).
With all attenuator probes, the maximum AC input voltage
must be derated with frequency usually above 20kHz.
Therefore the derating curve of the attenuator probe type
concerned must be taken into account.
The selection of the ground point on the test object is
important when displaying small signal voltages. It should
always be as close as possible to the measuring point. If this
is not done, serious signal distortion may result from spurious
currents through the ground leads or chassis parts. The
ground leads on attenuator probes are also particularly critical.
