Parallel resistance is normally caused by core losses. Air core coils generally have their losses dominated by the wire series resistance. You should be able to compare the DC resistance to Rs and see if they agree fairly closely. If so, then the series resistance approximation is the way to go. If there is a big discrepancy between DC resistance and Rs then parallel loss will probably give a better measure of inductance.
I have a General Radio 1650A Impedance Bridge. It has two positions for measuring unknown inductance, Lp (parallel inductance) and Ls (series inductance). The book is not clear as to the differences. I can get significant differences when measuring the same coil on the two settings.
The book says that Ls equals Lp within 1% when the Q of the coil is greater than 10. The coils I'm measuring have a Q of less than 10 at the bridge frequency of 1 Khz (2 or 3). Which scale should I use? What am I missing here?
Thanks Larry
Any combination of reactance (inductive or capacitive) and resistance may be represented as either a perfect reactance and resistance in series, or a perfect reactance and resistance in parallel. The values of both reactance and resistance in each case are *not* equal. The values of reactance in each case become close when Q>10.
With a Q between 2 and 3, the values of series and parallel reactance, hence inductance will differ significantly.
Which value to use? It all depends... In the case of small, air-cored coils, it is usual to use the series case. With big, iron-cored coils, the parallel case is usual.
Google for "hay maxwell bridge" - plenty of information.
Also try googling for "series parallel impedance conversion"
Omit the quotes in both cases.
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