IET Labs HARS-X Series, User And Service Manual

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6
OPERATION
HARS Series
3.2.4 Thermal emf Considerations
The highest-quality low-ernf components are used
in the
HARS-X Series. There nevertheless may be
some minute thermal emf generated at the test leads
where they contact the gold banana jacks.
This emf will not reflect itself if an ac measurement
instrument is employed. It will also be eliminated if a
meter with so called “True Ohm” capability is used.
Otherwise it may represent itself as a false compo-
nent of the dc resistance measurement.
3.3 Dial Setting
Whenever the dials are used in positions 0-9, the
resulting resistance is simply read directly. Both the
decimal point and the steps are clearly marked on
the panel.
For additional flexibility and range, each decade pro-
vides a “10” position setting. This “10” position on
any one decade equals the “1” position on the next
higher decade. It adds about 11% to the nominal
total decade resistance.
To determine the resistance obtained when one or
more “10” settings are used, simply add “1” to the
next higher decade. For example, a setting of
3-6-10-0-10
Ω
becomes:
3 3 0 0 0 0
6 6 0 0 0
10 1 0 0 0
0 0 0
10 1 0
____________________________
TOT 3 7 0 1 0
and a setting of 10-10-10-l0-10.10
Ω
becomes:
10 1 0 0 0 0 0.0
10 1 0 0 0 0.0
10 1 0 0 0.0
10 1 0 0.0
10 1 0.0
.10 1.0
________________________________
TOT 1 1 1 1 1 1.0
3.4 Environmental Conditions
For optimal accuracy, the decade box should be used
in an environment of 23
o C. It should be allowed to
stabilize at that temperature after any significant tem-
perature variation.
Humidity should be maintained at laboratory condi-
tions. This is especially important if high resistances
are involved.
Figure 3.1 Optimal 4-Wire Kelvin Lead Connection