5
OPERATION
HARS Series
Chapter 3
OPERATION
3.2.2 Electrical Considerations
In order to make proper use of the full performance
capabilities of the
HARS-X
unit, especially if low
resistance or low-resistance increments are impor-
tant, care must be taken in connecting to the termi-
nals of the decade box.
In particular, in order to keep contact resistance to
a minimum, the most substantial and secure connec-
tion to the binding posts should be made. They ac-
cept banana plugs, telephone tips, spade lugs, alli-
gator clips, and bare wire. The largest or heaviest
mating connection should be made, and, where ap-
plicable, the binding posts should be securely tight-
ened.
These considerations may be relaxed whenever
single milliohms are considered significant for the task
being performed.
3.2.3 Four-Wire Kelvin Lead Connections
Whenever possible, 4-wire Kelvin leads, the ideal
connection, should be employed. Such a connec-
tion minimizes the effects of contact resistance and
approaches ideal performance.
If the four terminals are available as clamps similar
to alligator clips, they may be connected to the necks
of the binding posts. If the four terminals are avail-
able separately, the optimal connection is shown in
Figure 3.1, where the current leads are introduced
into the top of the binding posts, and the voltage
leads at the necks.
3.1 Initial Inspection and Setup
This instrument was carefully inspected before ship-
ment. It should be in proper electrical and
mechanical order upon receipt.
An
OPERATING GUIDE
is attached to the case
of the instrument to provide ready reference to speci-
fications.
3.2 Connection
3.2.1 General Considerations
The
HARS-X
Series Decade unit provides three
terminals labeled
H
(high),
L
(low), and
G
(ground).
The
H
and
L
terminals are connected to the ends of
the resistance being set; the
G
terminal is connected
to the case. The
G
terminal may be used as a guard
or shield terminal. It may also be connected (using a
shorting link) to either terminal to allow two-termi-
nal as opposed to three-terminal measurements.
In order to make the most stable measurements,
determine which is the more sensitive of the two user
leads, i.e. the one going into a higher impedance.
This lead should be connected to the more protected
one of the two
HARS-X
terminals. That would ei-
ther be the
HARS-X
terminal that is shorted to the
case, or the
LOW HARS-X
terminal whenever nei-
ther is connected to the case.
Summary of Contents for HARS-X Series
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