Hameg HM504-2, Manual

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11
Subject to change without notice
With all attenuator probes, the maximum AC input voltage must
be derated with frequency, usually above 20 kHz. 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. 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
A: Basic settings
The following description assumes that:
1. “Component Tester” is switched off.
2. The following settings are present under MAIN MENU
> SETUP & INFO > MISCELLANEOUS:
2.1 CONTROL BEEP and ERROR BEEP activated (x),
2.2 QUICK START not activated.
3. The screen Readout is visible.
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 ), are electronically
set and interrogated. Thus, all electronically set functions and
their current settings can be stored and also remotely controlled.
B: Menu Display and Operation
Operation of some pushbuttons activates the display of menus.
There are Standard and Pulldown Menus.
Standard menus:
When a standard menu is displayed, all other readout information
(e.g. parameter settings) are switched off. The readout then
consists of the menu headline, and the respective menu functions.
At the bottom of the graticule are displayed symbols and
commands which can be operated by the pushbuttons related to
them below.
“Esc” CT pushbutton [37] switches one step back in the menu
hierarchy.
“Exit” SELECT – ON/OFF pushbutton [34] closes the menu and
switches back to the operating conditions present before calling
the menu.
The pushbuttons underneath the triangle symbols pointing
upwards UNIT CAL.SEL.
[35] and downwards SOURCE GLUE
[33] enable you to select one item which becomes highlighted.
The signal to be displayed can be connected directly to the Y input
of the oscilloscope with a shielded test cable such as
HZ32 or
HZ34 , or reduced through a x10 or x100 attenuator probe. The
use of test cables with high impedance circuits is only
recommended for relatively low frequencies (up to approx. 50 kHz).
For higher frequencies, the signal source must be of low
impedance, i.e. matched to the characteristic resistance of the
cable (as a rule 50 Ohm). Especially when transmitting square and
pulse signals, a resistor equal to the characteristic impedance of
the cable must also be connected across the cable directly at the
Y-input of the oscilloscope. When using a 50 Ohm cable such as
the
HZ34 , a 50 Ohm 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 2 Watts. This power is
reached with 10 V
rms
(28.3 V
pp
) 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 attenuator
probes, even high internal impedance sources are only slightly
loaded (approx. 10 MOhm II 12 pF or 100 MOhm II 5 pF 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 Y
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 an HF-adjustment 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 a 1 MHz calibrator, e.g.
HZ60 .
In fact the bandwidth and rise time of the oscilloscope are not
noticeably changed with these probe types and the waveform
reproduction fidelity can even be improved because the probe
can be matched to the oscilloscope’s individual pulse response.
If a x10 or x100 attenuator probe is used, DC input coupling
must always be used at voltages above 400 V. With AC
coupling of low frequency signals, the attenuation is no
longer independent of frequency, pulse tops can show pulse
tilts. Direct voltages are suppressed but charge 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 atte-
nuation probe which usually 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).
Controls and Readout