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Type of the signal voltage
With the HM 203-7, practically all periodically repeating sig¬
nals with the frequency spectrum below 20 MHz can be
examined. The display of simple electrical processes, such
as sinusoidal RF and LF signals or line frequency hum volt¬
ages is straightforward. When recording square-wave or
pulse-type signal voltages, it must be noted that their har¬
monics must also be transmitted. The repetition frequency
of the signal must therefore be significantly smaller than the
upper limit frequency of the vertical amplifier. Accurate
evaluation of such signals is only possible up to approxi¬
mately 2 MHz repetition frequency.
Displaying composite signals can be difficult, especially if
they contain no repetive higher amplitude content which
can be used for triggering. This is the case with bursts, for
instance. To obtain a well-triggered display in this case, the
assistance of the variable holdoff and/or variable time con¬
trol may be required.
Television video signals are relatively easyto trigger using
the built-in TV-Sync-Separator with correct trigger slope
setting.
For optional operation as a DC or AC voltage amplifier, the
vertical amplifier input is provided with a DC/AC switch.
The DC position should only be used with a series-con¬
nected attenuator probe or at very low frequencies or if the
measurement of the DC voltage content of the signal is
absolutely necessary.
When displaying very low frequency pulses, the flat tops
may be sloping with AC coupling of the vertical amplifier
(AC limit frequency approx. 1.6 Hz for -3dB). In this case,
DC operation is preferred, provided the signal voltage is not
superimposed on a too high DC level. Otherwise a capacitor
of adequate capacitance must be connected to the input of
the vertical amplifier with DC coupling. This capacitor must
have a sufficiently high breakdown voltage rating. DC cou¬
pling is also recommended for the display of logic and pulse
signals, especially if the pulse duty factor changes con¬
stantly. Otherwise the display will move upwards or down¬
wards at each change. Pure direct voltages can only be
measured with DC-coupling.
Amplitude Measurements
In general electrical engineering, alternating voltage data
normally refers to effective values (rms = root-mean-
square value). However, for signal magnitudes and voltage
designations in oscilloscope measurements, the peak-to-
peak voltage (Vpp) value is applied. The latter corresponds to
the real potential difference between the most positive and
most negative points of a signal waveform.
If a sinusoidal waveform, displayed on the oscilloscope
screen, is to be converted into an effective (rms) value, the
resulting peak-to-peak value must be divided by 2xy~2 =
2.83. Conversely, it should be observed that sinusoidal volt¬
ages indicated in
(Veff) have 2.83 times the potential dif¬
ference in Vpp. The relationship between the different volt¬
age magnitudes can be seen from the following figure.
Voltage values of a sine curve
V,ms = effective value; Vp = simple peak or crest value:
Vpp = peak-to-peak value:
'^mom =
momentary value.
The minimum signal voltage which must be applied to the Y
input for a trace of 1 div. height is ImVpp when the
Y
MAG.xS
pushbutton is depressed, the
VOLTS/DIV.
switch is set to
BmV/div.,
and the vernier is set to
CAL
by
turning the fine adjustment knob of the VOLTS/DIV.
switch clockwise all the way. However, smaller signals than
this may also be displayed. The deflection coefficients on
the input attenuators are indicated in
mV/div.
or
V/div.
(peak-to-peak value).
The magnitude of the applied voltage is ascertained by
multiplying the selected deflection coefficient by the
vertical display height in div.
If an attenuator probe xIOis used, a further multiplica¬
tion by a factor of 10 is required to ascertain the correct
voltage value.
For exact amplitude measurements, the variable con¬
trol on the attenuator switch must be set to its calibra¬
ted detent
CAL.
When turning the variable control ccw,
the sensitivity will be reduced by a factor of 2.5.
Therefore every intermediate value is possible within
the 1-2-5 sequence.
With direct connection to the vertical input,
signals up to
lOOVpp
may be displayed (attenuator set to
5V/div.,
vari¬
able control to left stop).
With the designations
H = display height in div.,
U
= signal
voltage in Vpp
at the vertical input,
D = deflection coefficient in V/div.
at attenuator switch,
the required quantity can be calculated from the two given
quantities:
U-DH
H.U
D = U
Subject to change without notice
M3 203-7
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