Voltage values of a sine curve
Vrms = effective value; Vp = simple peak or crest value;
Vpp = peak-to-peak value; Vmom = momentary value.
The minimum signal voltage required at the vertical
amplifier input for a display of 1cm is approximately
2mVpp.
This is achieved with the
AMPL.
attenuator
control set at
5mV/cm
and its
variable control in the ful
ly clockwise position.
However, smaller signals than
this may also be displayed. The
deflection coefficients
on the input attenuators are indicated in
mV/cm
or
V/cm
(peak-to-peak value).
For exact amplitude measurements, the variable con
trol on the attenuator switch must be set to its
calibrated detent
C.
The magnitude o f the applied voltage is ascertained by
multiplying the selected deflection coefficient by the
vertical display height in cm.
If an attenuator probe X I 0 is used, a further
multiplication by a factor o f 10 is required to ascertain
the correct voltage value.
With direct connection to the vertical input, signals up to
160Vpp may be displayed.
With the designations
H = display height in cm,
U
= signal
voltage in Vpp
at the vertical input,
D = deflection coefficient in V/cm
at attenuator switch,
the required quantity can be calculated from the two
given quantities:
U = D H
H = —
D = —
D
H
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 8cm, if possible 3.2 to 8cm,
U
between 2.5mVpp and 160Vpp,
D
between 5mV/cm and 20V/cm in 1 -2 -5 sequence.
Examples:
Set deflection coefficient D = 50mV/cm — 0.05V/cm,
observed display height
H
= 4.6cm,
required voltage U
= 0.05 • 4.6 =
0.2 3 Vpp.
Input voltage
U
= 5Vpp,
set deflection coefficient
D
= 1 V/cm,
required display height H = 5:1 = 5cm.
Signal voltage U = 220Vrms- 2 • j/2 = 622 Vpp
(voltage > 1 60Vpp, with probe X I 0:
U
= 62.2Vpp),
desired display height H = min. 3.2cm, max. 8cm,
max. deflection coefficient D = 62.2:3.2 = 1 9.4V/cm,
min. deflection coefficient D = 62.2:8
=7.8V /cm ,
adjusted deflection coefficient D = 10V/cm.
If the applied signal is superimposed on a DC (direct
voltage) level, the total value (DC
+
peak value o f the
alternating voltage) o f the signal across the Y-input
must not exceed ± 5 0 0 V .
This same limit applies to nor
mal attenuator probes X10, the attenuation ratio of
which allows signal voltages up to approximately
1,000Vpp to be evaluated. Voltages of up to approx
imately 3,000Vpp may be measured by using the HZ37
high voltage probe which has an attenuation ratio of
100:1 . It should be noted that its Vrms value is derated
at higher frequencies (see page M7: Connection of Test
Signal). If a normal X I 0 probe is used to measure high
voltages, there is the risk that the compensation trimmer
bridging the attenuator series resistor will break down
causing damage to the input of the oscilloscope.
However, if for example only the residual ripple of a high
voltage is to be displayed on the oscilloscope, a normal
X I 0 probe is sufficient. In this case, an appropriate high
voltage capacitor (approx. 22-68nF) must be connected
in series with the input tip of the probe.
It is very important that the oscilloscope input coupling is
set to
DC,
if an attenuator probe is used for voltages
higher than 500V (see page M7: Connection of Test
Signal).
With input coupling switched to
GD
and with the
Y-POS.
control, a horizontal graticule line can be adjusted as a
reference axis for ground potential.
It can be placed
underneath, on, or above the horizontal center line, as
the case may be to measure positive and/or negative
deviations from ground potential. Some switchable
probes have a built-in reference switch position for the
same application.
Time Measurements
As a rule, all signals to be displayed are periodically
repeating processes and can also be designated as
periods. The number of periods per second is the recur
rence frequency or repetition rate. One or more signal
M5 20 3-4
