Distortion Measurement

Definition of Nonlinear Distortion

The ratio of the effective value of all harmonic voltages to the effective value of the fundamental voltage.

Basic working principle of distortion meter

Figure 1 Principle diagram of fundamental wave suppression method

，

Active trap circuit (omitted)

Distortion meter example

Basic working principle

Figure 2 Principle block diagram of the distortion meter

When the distortion is less than 10%, γ≈ γ'

When the distortion is greater than 10%, it should be calculated and corrected according to the following formula:

2. Error analysis of distortion measurement

(1) Deviation between the distortion indicated by the instrument and the theoretical distortion

(2) It is difficult for the fundamental wave suppression network in the distortion meter to completely suppress the fundamental wave component.

Even if all the harmonics above the second harmonic are not attenuated, it is difficult to filter them out completely.

This will also cause certain measurement errors.

(3) The test instrument itself may also produce errors due to many reasons.

(4) The distortion read by the voltmeter should be deducted from the distortion of the instrument itself.

(5) If a peak or average voltmeter is used, a certain error will be introduced

(6) Notch filter

(7) Others