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attenuator probe is far below that of the
HM 205. Also these
probes do not normally have compensation facilities. There-
fore, wave form distortions cannot be excluded at high
repetition frequencies.
It is important that the sequence of firstly 1 kHz and then 1
MHz compensation
must be followed but need not be
repeated, also calibrator frequencies of 1 kHz and 1 MHz
cannot be used for time calibration. The pulse duty factor
also deviates from the value 1: 1. Short rise time, horizontal
pulse tops, calibrated pulse height and zero potential at the
pulse bottom are essential for exact attenuator probe com-
pensation. Frequency and pulse duty factor are not critical
here.
Low pulse rise time and low-impedance generator output
are particularly important for assessing the transmission
performance.
The calibrator of the HM
205 can even
replace expensive
square wave
generators with these
properties and the switchable frequency, e.g. when cali-
brating wideband attenuators or in the assessment of wide-
band amplifiers.
The test circuit can be connected via a suitable probe from
one of the HM 205 CAL. sockets. Plug the probe tip into the
0.2V output socket. Select either 1kHz or 1 MHz output fre-
quency. If your circuit has a high input impedance (e.g.
1MQI115-5O0pF
minimum) then use an attenator probe
such as x10 or x100. The applied signal will then be the CAL.
output divided by the probe attenuation e.g. 0.2V:10 =
20 mV etc. HAMEG probes type HZ37, 51, 52, HZ53 and 54
are suitable for this application. However if your circuit has
a low input impedance (e.g. 502), a x1 probe can be used
{in this case use a 50Q termination). The HAMEG HZ37,
HZ50, and HZ54 (x1 position) probes are suitable. The
switchable probes must be switched over to x1 and their HF
trimmer beneath the insulating cap of the BNC plug set to
the left stop. Approx. 40 mV,, is then obtained at the circuit
input (at 50 Ohm) with the HZ50 and approx. 17 and 24
MV,» With the HZ37 and 54, when the probe is inserted in
the 0.2 V CAL. socket. The voltage values stated here have
a tolerance larger than 1 % because 50 Ohm loading is not
normal for such a probe. Using the 2 V CAL. socket under
the same conditions is possible only with the HZ37 and
H2Z54. Then approx. 180 mV,, is obtained at 50 Ohm, with
around twice the normal rise time. More accurate voltage
values in the x1 mode can be measured immediately with
the HM 205 if a 50 Ohm through-termination HZ22 is con-
nected directly between the BNC plug output of the probe
and the Y input of the oscilloscope.
Operating modes of the vertical amplifiers
The desired operating mode of the vertical amplifiers is
selected with the 3 buttons in the Y field. All three buttons
out for mono mode. Only Channel lis then operational. The
button CH I/il-TRIG.V/I must be depressed in mono mode
for Channel Il. The internal triggering is simultaneously
switched over to Channel fl with this button.
If the DUAL button is depressed, both channels are work-
ing. Two signals can be displayed together in this button
position (alternate mode). This mode is not suitable for dis-
playing very slow-running processes. The display then flick-
ers too much or it appears to jump. If the CHOP. button is
depressed in addition to DUAL, both channels are switched
over constantly at a high frequency within a sweep period
(CHOP mode). Slow running processes below 1 kHz or
with time coefficients higher than 1ms/cm are then also
displayed without flicker. The dual mode chosen is less
important for signals with higher repetition frequency.
If the ADD button is depressed, the signals of both chan-
nels are algebraically added (+ | + II). Whether the resulting
display shows the sum or difference is dependent on the
phase relationship or the polarity of the signals and on the
positions of both INVERT buttons.
In-phase input voltages:
Both INVERT buttons released = sum.
Both INVERT buttons depressed = sum.
Only one INVERT button depressed = difference.
Antiphase input voltages:
Both INVERT buttons released = difference.
Both INVERT buttons depressed = difference.
Only one INVERT button depressed = sum.
In the ADD mode the vertical display position is dependent
upon the Y-POS. setting of both channels. The same
attenuator switch position is normally used for both chan-
nels with algebraic addition.
Differential measurement techniques allow direct meas-
urement of the voltage drop across floating components
(both ends above ground). Two identical probes should be
used for both vertical inputs. Using a separate ground con-
nection and not connecting the probe or cable shields to the
circuit under test avoid ground loops (hum, common-mode
disturbances).
X-Y Operation
For X-Y operation, the pushbutton in the X field marked X-Y¥
must be depressed. The X signal is then derived from the
Channel i (HOR. INP.). The calibration of the X signal
during X-Y operation is determined by the setting of
the Channel Il input attenuator and variable control.
This means that the sensitivity ranges and input imped-
ances are identical for both the X and Y axes. However, the
M10 205
Subject to change without notice
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