Hameg HM 2005 Manual Download Page 11

Page: 11 / 36

Subject to change without notice

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

Ω

). 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

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 2 Watts. This power is reached with 10V

rms

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

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 probe

HZ52

(x10 HF).

This can save the purchase of an oscilloscope with larger
bandwidth.
The probe mentioned has 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
noticeably 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 250V. With AC
coupling of low frequency signals, the attenuation 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. 250 V (DC + peak AC). DC input
coupling is therefore of quite special importance with a
x100 attenuation probe which usually has a voltage rating
of max. 120 0 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. 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 instrument is
not set to “COMPONENT TESTER” mode.

If the instrument is switched on, all important settings are
displayed in the readout. The LED´s located on the front panel
assist operation and indicate additional information. Incorrect
operation and the electrical end positions of control knobs are
indicated by a warning beep.

Except for the power pushbutton

(POWER)

, the calibrator

frequency pushbutton

(CAL. 1kHz/1MHz)

, the focus control

(FOCUS)

and the trace rotation control

(TR)

all other controls

are electronically selected. All other functions and their settings
can therefore be remote controlled and stored.

The front panel is subdivided into sections. – On the top,
immediately to the right of the CRT screen, the following controls
and LED indicators are placed.

(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 successfully,
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.
Some mode functions can be modified

(SETUP)

and/or

automated adjustment procedures (CALIBRATE) can be
called if the

“MAIN MENU”

is present.

For further infor-

mation please note “MENU”

(2) AUTOSET

Briefly depressing this pushbutton (

please note

“AUTOSET”

) automatically selects Yt mode. The instrument