Hameg HM 203, Руководство пользователя

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The time coefficient settings on the TIMEBASE switch
are calibrated when the variable control (small knob on
the
TIMEBASE switch) is set in the C position. When this
control is set fully clockwise, the sweep speed is
increased by a factor of at least 2.5. This factor is not
precisely calibrated. When the x5 expansion of the
sweep
(X-MAGN. X5 button pressed) is also operated in
conjunction with the variable control, a maximum sweep
speed
of approximately 40ns/cm is obtained
(TIMEBASE switch to O.BjUs/cm). The choice of the op­
timum time coefficient depends on the repetition rate of
the signal being measured. The number of cycles
displayed will increase with the time coefficient (by turn­
ing the TIMEBASE switch counterclockwise).
Component Tester
General
The HM203-4 has a built-in electronic Component
Tester (abbreviated
CT), which is used for an instant
display of a test pattern to indicate whether or not com­
ponents are in working condition. The
CT can be used for
quick checks of semiconductors (e.g. diodes and tran­
sistors), resistors, capacitors, and inductors. Certain
tests can also be made to integrated circuits. All these
components can be tested in and out of circuit.
The test priciple is of fascinating simplicity. The power
transformer of the HM203 delivers a sine voltage, which
feeds the series connection of the test object 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 the vertical deflection of the oscilloscope. So the
test pattern shows a current-voltage characteristic of the
test object.
Since this circuitry operates with mains/line frequency
(50 or 60Hz) and a voltage of 8.5V max. (open circuit),
the indicating range of the C7"is limited. The impedance
of the component under test is distinguishable in a range
from 20Q to 4.7 kQ. 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 borne in mind. However, the most im­
portant electronic components can normally be tested
without any restriction.
Setting and Component Connection
The CT is switched on by depressing the COMPONENT
TESTER pushbutton in the front panel section below the
CRT screen. Then both vertical preamplifiers and the
timebase generator are switched off. Nevertheless,
signal voltages at the three BNC connectors on front
panel are allowed. It is not necessary to remove their
cable connectors. However, this is valid only for the test
of single components (see below: In-Circuit Tests). In the
CT mode, the only controls which can be operated are
INTENS., FOCUS, and X-POS. The X-MAGN. X5
pushbutton should be released (out position). All other
controls and settings have no influence on the test opera­
tion.
For the connection of the component, two simple test
leads with 4mm 0 banana plugs, provided with test
prod, alligator clip or sprung hook at one end, are re­
quired. The test leads are connected to the insulated
CT
socket and an oscilloscope ground socket on front panel.
So the component has a bipolar connection.
To return the oscilloscope to normal operation, release
the
COMPONENT TESTER pushbutton.
Test Procedure
Caution! Do not test any component in live circuitry —
remove all grounds, power and signals connected to
the component under test. Set up Component Tester
as stated above. Connect test leads across component
to be tested. Observe oscilloscope display.
Test Pattern Displays
Page M l 3 shows the typical test pattern displayed by the
various components under test.
— Open circuit is indicated by a straight horizontal line.
— Short circuit is snown 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 pat­
tern 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.
The values of resistance from 20Q to 4 .7 kQ, can be
approximately evaluated. The determination of actual
values will come with experience, or by direct com­
parison with a component of a known value.
Testing Capacitors and Inductors
Capacitors and inductors cause a phase difference be­
tween current and voltage, therefore between the X and
Y deflections too, giving an ellipse-shaped display. The
position and opening width of the ellipse will vary accord­
ing to the impedance value (at 50 or 60Hz) of the com­
ponent under test.
M l 0 -2 03 -4
An ellipse in lying position indicates a high impedance