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Subject to change without notice
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
provides 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 Y deflection of the oscilloscope. The test pattern
shows the 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 Ohm to 4.7k Ohm. 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 Y amplifier 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 test prods, alligator clips or sprung
hooks, 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 connec-ted to the compo-
nent under test. Set up Compo-nent 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 value 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 Ohm to 4.7k
Ohm can be approximately evaluated. The determination of
actual values will come with experience, or by direct
comparison with a component of 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 low 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
Ohm to 4.7k Ohm can easily be obtained or compared.
Testing Semiconductors
Most semiconductor devices, such as diodes, Z-diodes,
transistors and 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 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 semiconductors 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.
The polarity of an unknown diode can be identified by com-
parison with a known diode.
Testing Transistors
Three different tests can be made to transistors: base-emitter,
base-collector and emitter-collector. The resulting test patterns
are shown below. The basic equivalent circuit of a transistor is
a Z-diode between base and emitter and a normal diode with
reverse polarity between base and collector in series
connection. There are three different test patterns:
For a transistor the figures b-e and b-c are important. The figure
e-c can vary; but a vertical line only shows short circuit condition.
These transistor test patterns are valid in most cases, but there
are exceptions to the rule (e.g. Darlington, FETs). With the
COMPONENT TESTER
, the distinction between a P-N-P to an
N-P-N transistor is discernible. In case of doubt, comparison
with a known type is helpful. It should be noted that the same
socket connection (CT
CT
CT
CT
CT or ground) for the same terminal is
Testing Capacitors and Inductors
