Operating Procedures; Instrument Turn-On - HP 333A Operating And Service Manual

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Section III
formation about the device under test than the
expression of distortion magnitude alone. Information
obtained from the oscilloscope pattern is specific and
reveals the nature of distortion which sometimes
occurs at such low levels that it is difficult to detect
in the presence of hum and noise. The impedance at
the OUTPUT terminals is 2000 ohms, therefore, ca-
pacitive loads greater than 50 pF should be avoided
to maintain the accuracy of meter readings.
3-14. OPERATING PROCEDURES.
3-15. INSTRUMENT TURN-ON.
a. Set the 115-230 VAC switch to coincide with the
line voltage in use. Turn switch to ON position.
Pilot lamp will glow, indicating application of
primary power.
3-16. ADJUSTMENT OF METER MECHANICAL
ZERO.
3-17. The meter is properly zero-set when the
pointer rests over the zero calibration mark and the
instrument is in its normal operating enivronment
and is turned off. Zero-set the meter as follows to
obtain maximum accuracy and mechanical stability:
a. Turn instrument· on and allow it to operate
for at least 20 minutes, to let meter move-
ment reach normal operating temperature.
b. Turn instrument off and allow 30 seconds
for all capacitors to discharge.
c. Rotate zero adjustment screw clockwise un-
til pointer is left of zero and moving upscale.
d. Continue rotating screw clockwise; stop when
pointer is exactly at zero.
e. When pointer ·is exactly over zero, rotate
adjustment screw slightly counterclockwise
to relieve tension on pointer suspension. Il
pointer moves off zero, repeat steps c through
e, but make counterclockwise rotation less.
3-18. DISTORTION MEASUREMENT.
DO NOT EXCEED THE INPUT VOLT-
AGES LISTED BELOW TO PREVENT
DAMAGING COMPONENTS ON A2
BOARD.
VOLTMETER FUNCTION -lV
RANGE AND BE LOW, AND
DISTORTION ANALYZER
FUNCTION - MAXIMUM
SENSITIVITY.
1. 300 V ABOVE 100 Hz
2. 50 V ABOVE 1 kHz
3-19. MANUAL MODE.
3-2
a. Turn instrument on and mechanically zero
meter according to procedure in Paragraphs
3-15 and 3-16.
Model 333A/334A
b.
Set NORM-R. F. DET. switch to NORM.
c. Set FUNCTION switch to SET LEVEL.
d. Set MODE switch to MANUAL.
e.
H
fundamental frequency is 1 kHz or greater,
set HIGH PASS FILTER switch to IN.
f. Set SENSITIVITY selector to
MIN.
position,
and rotate VERNIER control maximum
counterclockwise.
The bandwidth of the SENSI-
TIVITY selector is reduced
in the two extreme CCW
positions (positions used with
an input signal greater than
30 V}.
g. Set METER RANGE switch to SET LEVEL,
and set BALANCE COARSE and FINE con-
trols to center position.
h. Connect signal to be measured to 333A/334A
INPUT terminals.
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WARNING
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REMOVE SHORTING STRAP BETWEEN
FRAME GROUND ( .L.} AND CHASSIS
GROUND (
,& }
TERMINALS ON FRONT
PANEL INPUT TERMINALS WHEN
MEASURING DISTORTION BETWEEN
TWO POINTS WHICH ARE DC OFFSET
FROM GROUND POTENTIAL.
i. Set SENSITIVITY selector to obtain meter
indication greater than 1/3 full scale.
j. Adjust SENSITIVITY VERNIERfor full scale
meter indication if making distortion measure-
ment in percent; if making distortion measure-
ment in dB adjust SENSITIVITY VERNIER
for O dB meter indication.
~~~~~NOTE~~~~-
Il unable to adjust for full scale
or OdB indication, (which indicates
input signal is below O. 3 volts},
set METER RANGE selector down-
scale. Use this new setting as the
100%or
OdB
SET LEVEL position,
thus making the next range 30%
or -10 dB, etc.
k. Set FREQUENCY RANGE switch and frequency
dial to fundamental frequency of input signal.
1.
Set FUNCTION switch to DISTORTION.
m. Adjust frequency dial vernier and BALANCE
COARSE and
FINE
controls for minimum