35
Subject to change without notice
STORAGE MODE ONLY
In contrast to analog mode, intensity reduction does not occur.
But it must be noted that pulses of less than 20ns width are
displayed with too small amplitude. This is because of too
few samples per pulse, as in 200MSa/s condition (5ns
sampling interval) only 4 samples are taken.
Component Tester (analog mode)
General
The instrument specific information regarding the controls
and terminals are part of item
CT (46)
in section
“Controls
and Readout”
.
The instrument has a built-in electronic Component Tester,
which is used for instant display of a test pattern to indicate
whether or not components are faulty. It can be used for
quick checks of semiconductors (e.g. diodes and transistors),
resistors, capacitors, and inductors. Certain tests can also
be made to integrated circuits. All these components can be
tested individually, or in circuit provided that it is unpowered.
The test principle is fascinatingly simple. A built-in generator
delivers a sine voltage, which is applied across the component
under test and a built-in fixed resistor. The sine voltage across
the test object is used for the horizontal deflection, and the
voltage drop across the resistor (i.e. current through test
object) is used for vertical deflection of the oscilloscope. The
test pattern shows a current-voltage characteristic of the test
object.
The measurement range of the component tester is limited
and depends on the maximum test voltage and current
(please note data sheet). The impedance of the component
under test is limited to a range from approx. 20
Ω
to 4.7k
Ω
.
Below and above these values, the test pattern shows only
short-circuit or open-circuit. For the interpretation of the
displayed test pattern, these limits should always be born in
mind. However, most electronic components can normally
be tested without any restriction.
Using the Component Tester
After the component tester is switched on, the vertical
preamplifier and the time base generator are inoperative. A
shortened horizontal trace will be observed. It is not necessary
to disconnect scope input cables unless in-circuit measure-
ments are to be carried out.
For the component connection, two simple test leads with
4mm Ø banana plugs, and with test prod, alligator clip or
sprung hook, are required. The test leads are connected as
described in section
“Controls and Readout”
.
Test Procedure
Caution!
Do not test any component in live circuitry - remove
all grounds, power and signals connected to the com-
ponent under test. Set up Component Tester as sta-
ted. Connect test leads across component to be tes-
ted. Observe oscilloscope display.
Only discharged capacitors should be tested!
Test Pattern Displays
The “Test patterns” shows typical patterns displayed by the
various components under test.
• Open circuit is indicated by a straight horizontal line.
• Short circuit is shown by a straight vertical line.
Testing Resistors
If the test object has a linear ohmic resistance, both deflecting
voltages are in the same phase. The test pattern expected
from a resistor is therefore a sloping straight line. The angle
of slope is determined by the resistance of the resistor under
test. With high values of resistance, the slope will tend
towards the horizontal axis, and with low values, the slope
will move towards the vertical axis.
Values of resistance from 20
Ω
to 4.7k
Ω
can be approximately
evaluated. The determination of actual values will come with
experience, or by direct comparison with a component of a
known value.
Testing Capacitors and Inductors
Capacitors and inductors cause a phase difference between
current and voltage, and therefore between the X and Y
deflection, giving an ellipse-shaped display. The position and
opening width of the ellipse will vary according to the
impedance value (at 50Hz) of the component under test.
A horizontal ellipse indicates a high impedance or a relatively
small capacitance or a relatively high inductance.
A vertical ellipse indicates a small impedance or a relatively
large capacitance or a relatively small inductance.
A sloping ellipse means that the component has a consi-
derable ohmic resistance in addition to its reactance.
The values of capacitance of normal or electrolytic capacitors
from 0.1µF to 1000µF can be displayed and approximate
values obtained. More precise measurement can be obtained
in a smaller range by comparing the capacitor under test with
a capacitor of known value. Inductive components (coils,
transformers) can also be tested. The determination of the
value of inductance needs some experience, because indu-
ctors have usually a higher ohmic series resistance. However,
the impedance value (at 50Hz) of an inductor in the range
from 20
Ω
to 4.7k
Ω
can easily be obtained or compared.
Testing Semiconductors
Most semiconductor devices, such as diodes, Z-diodes,
transistors, FETs can be tested. The test pattern displays
vary according to the component type as shown in the figures
below. The main characteristic displayed during semicon-
ductor testing is the voltage dependent knee caused by the
junction changing from the conducting state to the non
conducting state. It should be noted that both the forward
and the reverse characteristic are displayed simultaneously.
This is a two-terminal test, therefore testing of transistor
amplification is not possible, but testing of a single junction
is easily and quickly possible. Since the test voltage applied
is only very low, all sections of most semi-conductors can be
tested without damage. However, checking the breakdown
or reverse voltage of high voltage semiconductors is not
possible. More important is testing components for open or
short-circuit, which from experience is most frequently need-
ed.
Testing Diodes
Diodes normally show at least their knee in the forward
characteristic. This is not valid for some high voltage diode
types, because they contain a series connection of several
diodes. Possibly only a small portion of the knee is visible.
Zener diodes always show their forward knee and, depending
Component Tester (analog mode)
