Applying DC Bias Current During an LCR Test
A conventional constant voltage power supply cannot be used with an LCR meter because its large output capacitance will swamp the inductive impedance of the device under test (DUT) and result in 100% measurement error.
A conventional DC Power Supply will Swamp Inductance Measurements
To overcome the problem of low power supply output impedance a large inductor (relative to the inductor being measured) may be inserted in series with the dc power supply in an attempt to isolate the DUT inductor from the DC power supply.
Using an Inductor to Isolate the PSU Cumbersome and Inaccurate
This is the technique most often used by LCR meter manufacturers when they design a Dc bias supply. However, the series inductor value may be very large and its self capacitance is likely to seriously affect the measurement. Also this large inductor value will have to be changed when measuring different inductor values.