Meter Indication; Manual Nulling; Distortion Measurement; Use Of Output Terminals - HP 333A Operating And Service Manual

Section
m
3-23. METER INDICATION.
3-24. The 333A/334A meter is calibrated to indicate
in both dB and volts. It is interesting to note that the
METER RANGE markings differ from most ac volt-
meter range markings. On most ac voltmeters (600
ohms) 0 dB corresponds
to
the 1 volt range. This is
not true in the case of the 333A/334A. Since the instru-
ment is primarily a distortion analyzer, measurements
are in dB (relative measurement) rather than in dBm
(absolute measurement). Zero dB on the 333A/334A
corresponds to 0. 3 volt range rather than the 1 volt
range. This allows a 10 dB greater dynamic range of
distortion measurements.
3-25. If measurements are to be made in dBm, 10 dB
must be subtracted from the METER RANGE setting.
Thus O dB becomes the -10 dBm range for absolute
power measurements. Zero dBm is equal to 1 milli-
watt dissipated
by
any impedance and in this particular
case is 600 ohms. The +10 DECIBELS marking on the
meter face indicates that when voltmeter measurements
are being made, the indication (METER RANGE plus
meter indication) is 10 dB greater than when power
(dBm) measurements are being made.
3-26. In short, when distortion and voltage measure-
ments are being made, utilize the instrument METER
RANGE and meter scale as they exist. For absolute
power measurements in dBm, simply subtract 10 dB
from the METER RANGE setting.
3-27. USE OF OUTPUT TERMINALS.
3-28. lnVOLTMETERand SET LEVEL functions, the
333A/334A can be used as a low distortion, wide-band
amplifier. A portion of the meter input (0. 1 V rms
open circuit for full scale meter deflection is provided
at the OUTPUT terminals.
3-29.
In
DISTORTION function, the distortion (0. 1 V
rms open circuit for full scale deflection) is provided
at the OUTPUT terminals for monitoring purposes.
3-4
~~~~~-NOTE~~~~~
The INPUT
,&
terminal and the
OUTPUT
,&
terminal should not be
connected directly together when
making low level measurements.
These terminals are isolated from
each other by 1 ohm which reduces
the effects of common mode voltages.
Model 333A/334A
3-30. 333A/334A WITH OPTION 01.
3-31. Operating procedures for the 333A/334A with
Option
O
1 are the same as for the standard instrument.
The only difference between the standard and optional
instrument is that the Option 01 has a special meter
and meter amplifier which is compensated to respond
to VU (volume unit) characteristics.
3-32. MANUAL NULLING.
3-33. Since the frequency and balance controls are
rather sensitive in the MANUAL mode, the following
information is supplied to simplify nulling the
333A/334A in the MANUAL mode. When nulling the
333A/334A in the MANUAL mode, connect the equip-
ment as shown below and adjust the 333A/334A fre-
quency and balance controls for the waveform shown
in step a below. Additional waveforms are provided
to simplify nulling.
a.
""1i.¥Ylti'klli
No harmonic distortion. Frequency
and balance adjustment correct.
Frequency and balance control im-
properly adjusted.
Frequency approximately correct;
balance incorrect.
d.
C:::::,
Balance approximately correct; fre-
quency incorrect.
e.
0 0
Second harmonic predominant; fre-
quency and balance adjusted.
f. .....----- Second harmonic predominant; fre-
quency and balance adjusted; phase
changed.
g. _____..... Second harmonic predominant; fre-
quency and balance adjusted; phase
changed.
h.
cx::x::>
Third harmonic predominant.
i . ~
j.o
Balance incorrect; meter reading of
scale.
Frequency incorrect; meter readinf
off scale.
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