HP 4328A Service Manual

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Model 4328A
3-47. On the 1 and 3m ohm ranges, currents flow-
ing in the current leads are 150 mA and 50 rnA respec-
tively large compared to other ranges. Moreover,
the voltmeter sechon has very high sensitivity, so
that, if a conductor surface is placed near and parallel
to the current loop, large errors may result due to
coupling between the current loop, the conductor and
the voltage terminals. Therefore, at 1 and 3m ohm
range, the probes and their cables (i.e. the part be-
tween the connector and the tip of probe) must be
placed lOcm or more away from the conducting sur-
face or the probes must be placed perpendicularly to
the conductor face ..
3-48. A 4- terminal measurement ts a method by
which resistance is accurately measured by removing
the effect of thermal emf and Lead wire resistance. If
a 4-termmal device is measured with the 4-terminal
method (Figure 3-9, a), the reading of the indtcating
meter will be an Rx which is accurate. However, when
measuring resistance by ustng only two terminals of
a 4-terminal device (as shown in Figure 3-9, b) the
meter will show the resistance of Rx + 2Re. Thus an
error of 2Re/Rx results in this instance. If Rx is
much larger than Re (Rx/Re> 1000), the error wtll be
withm specifications (±2%) even if measuring resist-
ance wtth the method shown in Figure 3-9b.
3-49. CHANGING TEST LEAD LENGTH.
3-50. The values in Table 3-2 are given for wire
lengths from the tip of test lead plug to the other end
of lead wire, and are maxtma for a single lead.. Note
that BOTH the resistance of lead wire AND the wire
length must be kept within the values shown in Table
3-2 at the same time.. Further it is recommended
that the 4 lead wires be used in a bundle as far as is
possible .. The wire length and wire quality of the other
two kinds of probes should not be changed.
4-TERMINAL DEVICE
VOLTAGE
TERMINAL
(a)
CURRENT
TERMINAL
s
Rx MEASURED RESISTANCE.
Section III
Paragraphs 3-47 to 3-50
Table 3-2. Maximum Values of Resistance
and Length of Lead Wire
Range Lead Wire
Lead Wire
(ohms)
Resistance
Length (em)
(ohms)
0.001
0.002-0.02*
40
0.003 0 06 60
0.01
0.2 100
0.03
0.6
200
0.1
2
200
0.3
6 200
1
20
200
3 20 200
10 20 200
30
20 200
100
20 200
•
Mimmum to maximum value shown.
4- TERMINAL DEVICE
.~
~
1
VOLTAGE
:TERMINAL
I
\
I
CURRENT
I
TERMINAL
I
r
I
I
(b)
Re RESISTANCE OF LEAD OR TERMINAL.
Ftgure 3-9. 4-Terminal Device Measurement
3-7

HP 4328A Specifications

General

Brand	HP
Model	4328A
Category	Measuring Instruments
Language	English