How to measure AC electrical resistance
Measurement electrical resistance alternating current can be produced by the ammeter - voltmeter method according to the diagrams of fig.
If it is necessary to determine the impedance components, use the three-instrument method of ammeter - voltmeter - wattmeter. Large resistances are measured according to the diagram in fig. 1, c, small resistances — according to the diagram in fig. 1, b. Impedance values are determined by the formulas
where P, U, I are the wattmeter, voltmeter and ammeter readings respectively.
The accuracy of these methods is low. They are used in determining the parameters of non-linear elements when the measurement is carried out under operational conditions.
To measure the impedance and its components, you can use the method of comparing the unknown resistance Zx with the known active resistance R0.
Rice. 1. Circuits for measuring resistances by the comparison method: a — series connection of the compared resistances; b — parallel
When Zx and R0 are connected in series (Fig.1, a), the total resistance and its components are determined by the formulas
With parallel connection of Zx and R0 (Fig. 1, b)
Various AC bridges are widely used to measure impedance as well as its active and reactive components. Bridges are supplied with current at the frequency at which measurements are required. Typically, the active and reactive components of the measured resistance are determined separately from the values of the controlled elements.
