8
HARS-LX Series
8
Operation
4.8 Meter Shunt Applications
To measure the current in a 4-terminal resistor:
1. Measure the voltage drop between the two
terminals of the resistor not connected to the
current source.
2. Determine the current by the ratio of the
measured voltage to the known resistance.
Using the 4-terminal technique helps avoid errors
caused by the voltage drops in the current-carrying
leads and contacts. Errors caused by lead and contact
resistances in the voltage measuring circuit are negli-
gible if the current in this circuit is small.
4.9 Kelvin Bridge Applications
Use 4-terminal resistance standard for all Kelvin
bridge measurements. When connected as shown in
Figure 4-1, errors caused by lead and contact resis-
tances can be made negligible because they appear as
part of the generator or yoke resistance, or in series
with high resistance bridge arms.
Figure 4-1: Kelvin Bridge Connections
HARS-LX
For maximum protection and accuracy, limit power
input to HARS-LX to 1 Watt. This may be accom-
plished by placing a resistor in series with the bridge
generator or battery.
The value of this resistance can be calculated from
the following formula:
where:
R = value of the power-limiting resistor
E = open circuit voltage of the generator
The protective resistor should have a power rating
of 4 W or more. Input power should be limited to
1/10 W or less for most accurate measurements.
R =
E
2
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