Tektronix 442, Инструкция по эксплуатации

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Operating Instructions—442 Service
the average dc level of the signal applied tothe probe. The
following procedure will prevent accidentally generated
voltage transients from being applied tothe preamplifier
circuit and also reduce the amount of charging current
drawn from the circuit under test.
1. Before connecting the probe tip to a signal source,
set the AC-GND-DC switch to GND in orderto establish a
reference.
2. Touch the probe tip to the 442 front panel ground.
Wait several seconds for the input coupling capacitor to
discharge.
3. Connect the probe tip to the test signal source.
4. Wait several seconds for the coupling capacitor to
charge.
5. Set the AC-GND-DC switch to AC. The display will
remain on the screen so the ac component of the signal
can be measured in the normal manner.
Operator’s Adjustments and Checks
To verify basic accuracy of the 442, make thefollowing
checks and adjustments. See Calibration section of this
Service manual for calibration information.
NOTE
When a 10X probe is used for making voltage
measurements, the deflection factor must be read
from the 10X window on the VOLTS/DIVknob skirt.
Probe Compensation
Improper probe compensation is a common source of
operator error. Probe compensation should be rechecked
when movi ng the probe from one oscilloscope to another
or when transferring the probe from one vertical input
channel to another on the same oscilloscope.
To compensate a 10X probe, connect its bnc connector
to either the channel 1 or channel 2 input connector and
touch the probe tip to the 442 front panel PROBE ADJ pin
connector. Set the appropriate VOLTS/DIV switch for a
displayed signal amplitude of 2 to 4 divisions. Set the
SEC/DIV switch to .1 m, and adjust TRIGGERING con­
trols for a triggered display. Adjust the probe compensa­
tion for a flat-top waveform (see Figure 2-10). Refer to the
appropriate probe data sheet or manual for the specific
method for compensating the probe in use.
ri
—
I
- — — ------
j— 4 - A
-
■ I PROPERLY
r COMPENSATED
+- ■ J WAVEFORM
■ J -— 1
1
1
1
j -COM PENSATED
—
. . .
V
—
|
—
— ------J
( 1 9 4 2 - 5 ) 2 3 7 4 -6 8
Figure 2-10. Probe compensation.
Vertical Gain Check
Obtain a display of the PROBE ADJ signal. Set the
VOLTS/DIV switch to .1 (the VOLTS/DIV VAR control
must be in the fully clockwise calibrated detent position).
Check that the amplitude of the displayed signal is about 5
divisions.
Basic Timing Check
With the SEC/DIV VAR control in the fully clockwise
calibrated detent position, obtain a normal sweep display
of a signal with a known frequency. Using the previous
setup for Vertical Gain Check, the PROBE ADJ signal
should display approximately one complete square-wave
cycle per graticule division with the SEC/DIVswitch setto
1 m.
W A R N I N G
To prevent possible cross grounding if the power
input voltage is used as a signal source, do not
attach the probe ground clip to either side of the line
voltage source. The 442 chassis ground provides an
adequate ground reference.
To use the power line frequency for a basic timing
check, lay the 10X probe tip near the power cord and
adjust the VOLTS/DIV switch for a vertical display
amplitude of several divisions. Set the SEC/DIV switch to
display one complete cycle over several horizontal
graticule divisions. Duration = 1/frequency. If a 60 Hz
power line frequency is being used, check that the
duration of one complete cycle is 8.35 divisions with the
SEC/DIV switch set to 2 m; and if the SEC/DIV switch is
set to 10 m, six cycles of signal should be displayed within
the graticule area (adjust LEVEL and other TRIGGERING
controls as required to provide a stable triggered display
of the signal being used).
REV A MAY 1980
2-9