1: turn ratio (TR): Ratio between primary and secondary turns, which measures transformer coils turns ratio and coupling coefficient.
2: phase (PH): winding direction which detects winding directions of primary and secondary coils.
Inductance value: proportional coefficient (e=L) between time rate change of voltage and current, which detects iron core magnetic permeability µ, mechanics size, integrity and absolute number of windings.
Inductance value with bias DC superposition: Detects magnetic saturation characteristics of iron core.
Leakage inductance: equivalent inductance created by leakage flux cutting, which measures iron core magnetic permeability µ and winding generated coupling coefficient.
6: quality factor Q: ratio between inductive impedance (2πfL) and resistance (ACR).
7: capacities between coils (Cp): Stray capacitance between coils, which measures distance between coils, insulation materials and isolation design.
8: DC resistance: DCR: copper resistance, which detects PIN welding points, copper materials, designed wire length and open/short circuits.
9: AC resistance ACR: equivalent resistance generated by copper resistance with hysteretic lost and vortex. Besides copper wires, iron core magnetization and insulation can be detected as well.
10: Impedance: AC Absolute impedance of transformers.
12: Balance: Balance test between two groups on transformer windings, which measures inductance equivalence and resistance balance.
13: Pin short circuit: short circuits between un-connected pins, which detects short circuits between coils created by enameling and soldering.

Introductions to measurement technologies of magnetic components
1：Correct short circuit zeroing: Incorrect short circuit will affect measurement precision on inductance value, quality factor and equal serial resistance etc.

Correct short circuit connection

2: Correct open circuit zeroing: Incorrect open circuit reset will affect measurement precision on high inductance value and high frequency. Distributed capacitor can be removed by ground the middle insulation part.

Correct open circuit connection

3: Precaution of 4 points measurement

Wiring impedance and contact impedance will occur in two points measurement, both of which will cause error. Contact impedance is main root cause of instability and it can decrease the stability and certainty of low inductance measurement, quality factor, ESR and impedance directly. All affects can be removed in four points measurement.

DC resistance in 2 points measurement DC resistance in 4 points measurement Example of low inductance Core testing Sensing, probe, Core, copper plate (a) 3 points contact Vertical, Hp, Lp (b) 4points measurement

4: Nonlinear feature of inductance

Linear zone of iron core is used to display inductance value, but it is uncertain to designate the linear zone so even the in that zone the inductance does not show linearly. Besides that, relationship between measurement current Im, measurement voltage Vm, device output impedance Zo and Inductance impedance Zx is:

It can be seen that when output impedance of measurement device Zo changes, even specified measurement voltages are same, and the actual measurement voltages Vm of unit under test are still different.
5: temperature change