Operating Procedures; Distortion Measurement - HP 333A Technical Manual

TM 11-6625-1576-15
Section III
Paragraphs 3-16 to 3-22
about the device under test than the expression of dis-
tortion magnitude alone.
the oscilloscope pattern is specific and reveals the
nature of the distortion that 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, capacitive loads
greater than 50 pf should 'be avoided to maintain the
accuracy of meter readings.
3-16. OPERATING PROCEDURES.
3-17. The 333A and 334A Distortion Analyzers can be
operated from an ac power source ( 115/230 volt) or a
dc power source (+28 to +50 and -28 to -50 volt source).
If a dc source is used, check the -25 v output. If
necessary, adjust the power supply according to the
procedures in Paragraph 5-27.

3-18. DISTORTION MEASUREMENT.

3- 19. DISTORTION MEASUREMENT IN PERCENT,
AUTOMATIC MODE.
a. Position FUNCTION selector to SET LEVEL.
b. Position MODE switch to MANUAL.
c. If fundamental frequency is 1 Kc or greater,
position HIGH PASS FILTER SWITCH to IN.
d. Rotate SENSITIVITY selector to MIN position.
NOTE
The bandwith of the SENSITIVITY se-
lector is reduced in the two extreme
CCW positions (positions used with an
input signal greater than 30 v).
e. Position METER RANGE selector to SET LEVEL
100%).
f. Connect test leads from device under test to
INPUT terminals.
REMOVE SHORTING STRAP BETWEEN
FLOATING GROUND ~ AND CHASSIS
GROUND (+) TERMINALS ON FRONT
PANEL INPUT TERMINALS WHEN
MEASURING DISTORTION BETWEEN
TWO POINTS WHICH ARE BOTH ABOVE
GROUND POTENTIAL.
g. With SENSITIVITY VERNIER control max. CCW,
position SENSITIVITY selector for meter indication
greater than 1/3 full scale.
NOTE
If unable to adjust for full scale deflec-
tion which indicates input signal is be-
low O. 3 volts, use manual mode and
position METER RANGE selector down-
scale. Use this new position as the 100%
SET LEVEL position, thus making the
next range 30%, etc.
h. Adjust SENSITIVITY VENIER control for full
scale deflection.
j. Position FRIQUENCY RANGE selector and
frequency dial to fundamental frequency of input signal.
3-2
Information obtained from
k. Position FUNCTION selector to DISTORTION,
m. Adjust METER RANGE selector and frequency
dial vernier control for minimum meter indication.
n. Adjust COARSE and FINE BALANCE controls
for further reduction of meter indication. Meter indi-
cation must be less than 10%of SET LEVEL indication.
p. Position MODE switch to AUTOMATIC.
r. Observe percentage of distortion indicated on
meter. Meter indication is in conjunction with METER
RANGE selector. For example, if meter indicates
.4 and METER RANGE selector is on 1% position,
distortion measured is 0.4%.
NOTE
RMS voltage of input signal being ana-
lyzed for distortion can be measured
by positioning FUNCTION selector to
VOLTMETER position.
DISTORTION MEASUREMENT IN PERCENT,
3-20.
MANUAL MODE.
NOTE
In MANUAL mode the accuracy of dis -
tortion measurements is affected by
frequency stability of the input signal.
An inaccuracy in distortion indications
occure when the frequency drift of the in-
put signal exceeds the bandwidth of the
rejection curve.
a. Perform steps a through n in Paragraph 3-19.
b. Repeat steps m and n until no further reduction
-
in meter indication can be obtained.
c. Observe percentage of distortion indicated on
meter.
3-21. DISTORTION MEASUREMENT IN DB,
AUTOMATIC MODE .
a. Perform steps a through g of Paragraph 3-19.
b. Adjust SENSITIVITY VERNIER control for 0 db
meter indication.
c. Perform steps
d. Observe meter indication for distortion in db.
NOTE
Distortion in db is obtained by alge-
braically adding meter indication to
db indicated by METER RANGE se-
lector: for example, If meter indi-
cates -2 and METER RANGE selec-
tor is on -20 db position, distortion
measured is -22 db.
3-22. DISTORTION MEASUREMENT IN DB, MANUAL
MODE .
NOTE
Notes in Paragraphs 3-20 and 3-21
apply.
a. Perform steps a through g of Paragraph 3-19.
b. Adjust SENSITIVITY VERNIER control for O db
meter indication.
Model 333A/334A
j through 3-19.