2.8 LOSS BALANCE-Q OR D
The LOSS BALANCE contrai enable s the resistive loss of an impe danc e
under test to be balanced out so that the true reactance ofthe component may
be measured more accurately.
When me a suring capacitor s on this bridge the LOSS BALANCE controls
are normally set to D, which gives the resultin terms of series capacitance,
Cs, and series resistance Rs. The dissipation factor, D = 21TfCsRs' When
the LOSS BALANCE is set toQ the parallel values, Cpand Rp' are measured;
bere Q = 21TfCpRp'
C l + Q2 2 .
-.§. = = l + D Slnce D = l/Q
C Q2
P
It will be seen that far values of Q greater than lO (D less than O. l)
Cs = Cp, within '1"/0.
Measurements on inductors are more dependent on their care loss
far LOSS BALANCE setting. Normalair coredcoils are measured in terms
ofseriesinductance Lsand seriesresistance, Rs' withthe LOSS BALANCE
at the Q setting.
21TiL
Here Q = ~
Rs
High Q coils, such as ferrite coredfilter coils, are measured in terme
of parallel values Lp and Rp' on the D x .01 range. This is equivalent to a
Q range of lO to 00, and far values of Q greater than lO, L = Ls, within
1%. With laminated iron cored inductors the predominant foss, due to the
care, takes the form of parallel resistance and is measured on the D x l
range.
21TiL Lp 2
Here D = ~ and r;; = l + D
Q and D with External A. F.
TheQ andD ranges are proportional to frequency so that at frequencies
lower than l kcl s the Q range may be insufficient and recour se to the D x l
range must be made with a parallelI series conversion as above if required.
The correct adjustment of the LOSS BALANCE becomes increasingly
criticaI at high frequencies when using D and at low frequencies using Q.
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