Autoset; Component Test - Hameg HM400 Manual

7 AUTOSET

See also the information given under AUTOSET
Controls
As mentioned in the chapter Controls all front panel controls are
electronically read out, hence the instrument can also be completely
electronically controlled. This allows for a fully automatic signal-derived
setting of all controls in the Yt mode. In most cases manual settings will
be superfluous. When AUTOSET is activated, the instrument will enter
the Yt mode if XY was selected; if it was already in Yt mode, the settings
will remain unaffected unless ADD was selected which will be set to
DUAL. In one-channel mode the sensitivity is automatically chosen so
that the signal will be displayed with appr. 6 divisions; in DUAL channel
mode each channel display will be appr. 4 divisions.
The foregoing and the description of the time base setting apply to
signals which do not differ too much from a duty cycle of 1:1. The auto-
matic selection of a suitable time base speed will show appr. 2 signal
periods. With signals which contain several frequencies the settings
obtained are governed by chance.
Pressing the AUTOSET button will have these results:
– The input coupling (AC, DC) remains unchanged resp. the last
setting before switching to GND is resumed.
– Internal triggering.
– Automatic triggering.
– Automatic selection of the trigger source
– The trigger level will be set to the center of its range.
– VOLTS/DIV set to calibrated (variables off)
– TIME/DIV set to calibrated (variable off)
– AC or DC trigger coupling unchanged
– Magnifier off
– X and Y positions automatic
– Trigger slope selection unchanged
– Visible trace
Selecting AUTOSET will leave the selected AC or DC input coupling
unchanged. In case DC trigger coupling was selected, this will not be
changed to AC. The automatic triggering functions without peak-to-peak
detection. The AUTOSET settings will override any former settings. In
case variables were activated, they will be disabled, such that all settings
will be calibrated. After AUTOSET was activated, manual control can
be executed. Due to the reduced bandwidth in 1 and 2 mV/DIV these
ranges will not be used in AUTOSET.
If a pulse signal is applied the duty cycle of which reaches
or exceeds 1:400, an automatic display will in most cases
become impossible. In such cases only the freerunning
trace will be visible.
It is recommended to switch to normal trigger mode and to set the
trigger point about 5 mm above or below the screen center. If the TRIG'd
LED lights up, the signal was recognized. In order to render it visible,
the time base speed and the sensitivity must be increased, however, the
trace may dim so much that the pulse may remain invisible.

8 Component test

The oscilloscope HM400 has a built-in component tester which is
7
in the chapter activated by pressing the mode button COMP . The unit under test is
connected to the two contacts right and left below the screen. After
pressing the COMP button, the Y preamplifiers and the time base will
be disconnected. While using the component tester, signals may be
present at the inputs as long as the unit under test is not connected to
any other circuit. It is possible to test components remaining in their
circuits, but in such cases all signals must be disconnected from the
three front panel BNC connectors! (See the following paragraph: „Test
in circuits"). With the exception of the SELECT button
buttons, and the X-POSITION
all other controls will be disabled. Two cables with 4 mm plugs are
necessary to connect the unit under test to the component tester. After
completion of the component test pressing the COMP button again is
all that is needed to resume normal scope operation.
The test principle is quite simple. A generator within the HM400 ge-
nerates a 50 Hz ±10 % sine wave which feeds the series connection
of the test object and a sense resistor. The sine wave voltage is used
for the X deflection and the voltage drop across the resistor for the
Y deflection.
If the test object has only a real part such as a resistor, both deflection
voltages will be in phase; the display will be a straight line, more or less
slanted. Is the test object short-circuited, the line will be vertical (no vol-
tage, current maximum). If the test object is open-circuited or missing
a horizontal line will appear (voltage, but no current). The angle of the
line with the horizontal is a measure of the resistance value, allowing
for measurements of resistors between 20 Ω and 4.7 K.
Capacitors and inductors cause phase shift between voltage and current
and hence between the deflection voltages. This will cause displays of
ellipses. The location and the form factor of the ellipse are determined
by the apparent impedance at 50 Hz. Capacitors can be measured
between 0.1 and 1000 µF.
– An ellipse with its longer axis horizontal indicates a high impedance
(small capacitance or large inductance)
– An ellipse with its longer axis vertical indicates a low impedance
(large capacitance or small inductance)
– An ellipse with its longer axis slanted indicates a relatively large
resistive loss in series with the impedance of the capacitor or
inductor.
With semiconductors the transition from the non-conducting to the
conducting state will be indicated in their characteristic. As far as
is possible with the available voltages and currents the forward and
backward characteristics are displayed (e.g. with zener diodes up to 9
V). Because this is a two-pole measurement, the gain of a transistor
can not be determined, however, the B-C, B-E, C-E diodes can be mea-
sured. Please note that most bipolar transistors can only take an E-B
C o m p o n e n t t e s t
13
knob, and the X-MAG/x 10
As outlined in the chapter Safety, all measurement con-
nectors are connected to the mains safety earth (in proper
operation). This implies also the COMP.TESTER contacts.
As long as individual components are tested, this is of no
consequence because these components are not con-
nected to the mains safety earth.
If components are to be tested which are located in
circuits or instruments, these circuits resp. instruments
must be disconnected first under all circumstances! If
they are operated from the mains, the mains plug of the
test object has to be pulled out. This ensures that there
will be no loops between the scope and the test object via
the safety earth which might cause false results.
Only discharged capacitors may be tested!
Subject to change without notice
4 2
, the ADJUST
12
button
37