The method and principle of measuring AC voltage with a multimeter
Because the measuring device of multimeter is DC microampere head, so when measuring AC voltage, it must introduce rectifier element to constitute rectifier system of AC voltmeter. The AC voltage block of the multimeter is the AC voltmeter with enough current system.
Multimeter rectifier circuit, can use half-wave rectification and full-wave rectification. After the rectification of the average current, you can apply the method of measuring DC voltage to measure the AC voltage. As people are always accustomed to the effective value to measure the AC voltage, so the system on the dial of the multimeter is also expressed in effective value. Sinusoidal alternating current of the effective current I and the ratio of the average current I, known as the waveform coefficient to Kf to express. For full-wave rectification Kf = 1.11, for half-wave rectification Kf = 2.22.
In fact, the multimeter AC voltage measurement circuit, more than half-wave current mode. Visible from the cause, when the measured AC voltage positive half-week, half-wave rectified current through the positive terminal in, multiplying resistance R3, R2, R1, Z1, flow through the ammeter head to the negative terminal. When the measured AC voltage is negative half-cycle, z1 cutoff, no current flows through the meter head, and the rectified current flows through z2, R1, R2 R3 from the positive terminal. The rectifier in the multimeter generally uses a semiconductor rectifier. AC voltage measurement, there are generally the following two methods, one is the measurement of AC and DC voltage, a common set of multiplier resistors, and draw a scale line on each dial.
However, up to two engraved skin line on the voltage value is far apart, so these two scale lines -k are to be labeled with the value of the voltage. Another is the continental amount of AC and DC voltage, each with a set of multiplier resistors, so that AC and DC voltage scales can be used with the same scale line.
