Subject to change without notice
8
Type of signal voltage
The following description of the
HM1507-2
relates to the
analog-oscilloscope mode. Please note
“Storage Opera-
tion”
.
The oscilloscope
HM1507-2
allows examination of DC vol-
tages and most repetitive signals in the frequency range up
to at least 150MHz (-3dB).
The vertical amplifiers have been designed for minimum
overshoot and therefore permit a true signal display.
The display of sinusoidal signals within the bandwidth limits
causes no problems, but an increasing error in measurement
due to gain reduction must be taken into account when
measuring high frequency signals. This error becomes
noticeable at approx.
70MHz.
At approx.
110MHz
the redu-
ction is approx. 10% and the real voltage value is 11% higher.
The gain reduction error can not be defined exactly as the
-
3dB
bandwidth of the amplifiers differ
between 150MHz
and 170MHz.
For sine wave signals the -6dB limit is approx. 220MHz.
When examining square or pulse type waveforms, attention
must be paid to the harmonic content of such signals. The
repetition frequency (fundamental frequency) of the signal
must therefore be significantly smaller than the upper limit
frequency of the vertical amplifier.
Displaying composite signals can be difficult, especially if they
contain no repetitive 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 hold off function or the second time base may
be required. Television video signals are relatively easy to
trigger using the built-in
TV-Sync-Separator (TV)
.
For optional operation as a
DC
or
AC
voltage amplifier, each
vertical amplifier input is provided with a
DC/AC
switch. DC
coupling should only be used with a series-connected atte-
nuator probe or at very low frequencies or if the measure-
ment 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
coupling is
also recommended for the display of logic and pulse signals,
especially if the pulse duty factor changes constantly.
Otherwise the display will move upwards or downwards at
each change. Pure direct voltages can only be measured with
DC
coupling.
The input coupling is selectable by the AC/DC pushbutton.
The actual setting is displayed in the readout with the “
=
“
symbol for
DC
- and the “
~
“ symbol for
AC
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 desi-
gnations in oscilloscope measurements, the peak-to-peak
voltage (V
pp
) 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 2x
√
2 = 2.83. Conversely, it
should be observed that sinusoidal voltages indicated in V
rms
(V
eff
) have 2.83 times the potential difference in V
pp
.
The relationship between the different voltage magnitudes
can be seen from the following figure.
Voltage values of a sine curve
V
rms
= effective value; V
p
= simple peak or crest value;
V
pp
= peak-to-peak value; V
mom
= momentary value.
The minimum signal voltage which must be applied to the Y
input for a trace of 1div height is 1mV
pp
(± 5%) when this
deflection coefficient is displayed on the screen (readout)
and the vernier is switched off (VAR-LED dark). However,
smaller signals than this may also be displayed. The deflection
coefficients 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 x10 is used, a
further multiplication by a factor of 10 is required to ascertain
the correct voltage value.
For exact amplitude measurements, the variable control (VAR)
must be set to its calibrated detent CAL position.
With the variable control activated the deflection sensitivity
can be reduced up to a ratio of 2.5 to 1 (
please note “controls
and readout”
). Therefore any intermediate value is possible
within the 1-2-5 sequence of the attenuator(s).
With direct connection to the vertical input, signals
up to 400Vpp may be displayed (attenuator set to
20V/div, variable control to 2.5:1).
With the designations
H
= display height in div,
U
= signal voltage in V
pp
at the vertical input,
D
= deflection coefficient in V/div at attenuator switch,
the required value can be calculated from the two given
quantities:
However, these three values are not freely selectable.
They have to be within the following limits (trigger threshold,
accuracy of reading):
H
between 0.5 and 8div, if possible 3.2 to 8div,
U
between 0.5mV
pp
and 160V
pp
,
D
between 1mV/div and 20V/div in 1-2-5 sequence.
Type of signal voltage
