Subject to change without notice
30
Component Tester
Component Tester
General
The instrument specific information regarding the control and
terminals are part of item
(39)
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
measurements 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 compo-
nent under test. Set up Component Tester as stated.
Connect test leads across component to be tested.
Observe oscilloscope display.
Only discharged capacitors should be tested!
Test Pattern Displays
The page ”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 considerable
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 inductors
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 semiconductor
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 needed.
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
on the test voltage, their zener breakdown forms a second
knee in the opposite direction. If the breakdown voltage is
higher than the positive or negative voltage peak of the test
voltage, it can not be displayed.
