HP 4328A Service Manual

A
Model4328A
by means of measuring instruments with voltage peak
values of 20mV or less.
3-20. The instrument can not start oscillating H no
sample is connected between the probes .. When sam-
ple is connected between the probes, a positive feed-
back loop is formed, and the oscillator begins oscil-
lation. Since constant current flows in the sample (in
correct range setting), voltages across the sample
are proportional to sample resistance and are less
than . 2m V peak on any range, at full scale deflection.
When the resistance value of the sample is greater
than that of the set range, an "over-voltage" protec-
tion circuit ln the Model 4328A i.s called upon to pre-
vent any voltage higher than 20mV peak from belng
applied to the sample.. Thus, when an unknown sam-
ple IS measured without special preparation, contact
resistance is still accurately measurable without dis-
turbance to the contact points.
3-21. APPLlED CURRENT ON SAMPLES AND
MAXIMUM
POWER DISSIPATlON
3-22. With Model 4328A, the current and power ap-
plied to samples are extremely small, the maxima at
measurement (i. e, when the meter needle deflects
full scale) being as shown in the table below.
Table 3-1. Characteristics of Applied Cur-rent
on Samples and Maximum Power Dissipation
MEASURING *1
POWER
*2
RANGE
CURRENT DISSIP A TlON
(Ohm) (rnA)
(/lW)
0. 001
150
23
0. 003
50
8
0.01
15 2.3
0.03
5
0.8
0 1
1.5 0.23
0. 3
0.5 0 .. 08
l
0 .. 15
0 .. 023
3
0 .. 05
0.008
10
0. 015
0. 0023
30
0
.. 005 0.0008
100
0.0015
0.00023
* 1 Constant to each range.
*2 Propo-rtional to meter deflection,
against full scale deflectwn ..
3-23. As shown in the above table, the power dissi-
pation at sample is so small that fuses, detonators
and semi-conductors can be safely measured.
3-24 EFF.Ii:CT OF SERlES REACTANCE OF
SAMPLES
3-25. The meter circuit of Model 4328A does not
(within limits) respond to the series reactance of --a
sample. The meter mdtcates only the correct value
of the pure resistance of the sample as long as the
series reactance of the sample at 1kHz is less than
twice full scale resistance value.
3-26. DC BIAS SUPERIMPOSED
3-27 DC bias may be present on samples, due to
Section III
Paragraphs 3-20 to 3-34
some source. Model4328A measures with ac (1kHz),
but its probe ctrcuits incorporate de blocktng capaci-
tors The mstrument will not burn out nor will any
measuring error will occur even when the probes come
in direct contact With a de circuit. The maximum de
voltage applicable between two probes is 150V.
3-28.. Also, as the probes are floating from the in-
strument case (able to Withstand voltage up to 500V
de; insulation resistance 10Mr2 or over), it is possible
to measure the resistance value of a sample having
de voltages relative to ground by connecting directly
to it.
3-29. The dynamic resistance of elements whose V-1
characteristics shownon-hnearittes, (such as diodes)
may be measured at an arbitrary DC bias pomt. In
this type of measurement, note that the maximum
voltage (1 kHz) applied to the sample is 0. 2mV peak
or less ..
3-30. RECORDER OUTPUT
3-31. A RECORDER termmal is provided on the rear
panel of the 4328A, providing a de voltage proportional
to the resistance of the sample permitting recording
of consecutive tests, etc.
3-32. PROBE CONNECTIONS.
3-33. General
3-34. In Model 4328A, measurement is made by the
4-terminal method; special two-terminal probes that
can make 4-terminal measurements (16005A Clip-
type Probes and 16006A Pin-type Probes), and con-
ventional4-terminal testleads (16007 A/B Test Leads)
are furnished, and can be mixed or matched depend-
ing on sample type For eKample, in the case of
measurement of the contact resistance of printed cir-
cuit board connectors, 1t is usually convenient to use
a combination of the clip-type probe and the pin-type
probe as shown in Figure 3-4.
Figure 3-4. Probe Combination
3-5

HP 4328A Specifications

General

Brand	HP
Model	4328A
Category	Measuring Instruments
Language	English