Appendix 3. Effect Of Eddy Currents And Suggested Solution; Effect Of Eddy Currents; Suggested Scheme: Separate The Sense And Source Cables - Fluke BT5300 Series User Manual

Appendix 3. Effect of Eddy Currents and Suggested Solution

Effect of Eddy Currents

To measure the internal resistance of the battery, the SOURCE terminals output a AC current (about
1 kHz) across the battery, this current flows the internal resistance of the battery, resulting in a voltage
with the same phase as the AC current, and this voltage is acquired by the SENSE terminals; then the
internal resistance of the battery can be calculated based on the proportion and phase relations
between the voltage acquired by SENSE terminals and the current output by SOURCE terminals.
When current flows through SOURCE wires, an alternating magnetic field is generated; this
alternating magnetic field generates an induced voltage on the nearby SENSE wires. Ideally, there is
no loss in the alternating magnetic field, and the voltage induced by the magnetic field is 90° out of
phase with the alternating current. The battery tester can detect the phase of the measured voltage,
and allows the induced voltage has no effect on the measurement of the battery's internal resistance.
In actual measurement, if there is a conductive object around the wire, the alternating magnetic field
generates an eddy current in the conductive object. This eddy current has energy loss, which shifts
the phase of the magnetic field induced voltage, so that the component with the same phase with the
current occurs in the SENSE voltage. This in-phase components are superimposed on the voltage
generated by the internal resistance, causing error in measurements.

Suggested Scheme: Separate the SENSE and SOURCE cables

SOURCE HI
SOURCE LO
SENCE HI
SENCE LO
SOURCE and SENSE lines are separated,
which is not easy to introduce eddy current effects
In the design of the Fluke test lead, the SENSE and SOUCE lines connected to the Instrument are
separated. This design ensures that most area of the test lead are hardly affected by eddy currents
and ensure the stability of the data during manual testing.
Figure 52. BTL310 test lead
Battery Tester
Appendix
SOURCE HI
SENCE HI
SENCE LO
SOURCE LO
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