How does a multimeter measure AC voltage
How does the multimeter measure AC voltage? The rectifier circuit of the multimeter can use half-wave rectification and full-wave rectification. The average current after rectification can be applied to measure the DC voltage to measure the AC voltage.
Multimeter to measure AC voltage
Since the measuring device of the multimeter is a DC microammeter head, when measuring the AC voltage, a rectifier element must be introduced to form an AC voltmeter of the rectifier system.
The AC voltage block of the multimeter is a multi-range AC voltmeter. The rectifier circuit of the multimeter can use half-wave rectification and full-wave rectification.
The average current after rectification can be applied to measure the DC voltage to measure the AC voltage.
Since people are accustomed to measuring AC voltage in effective value, the system on the dial of the multimeter is also expressed in effective value. The ratio of the effective current I of the sinusoidal alternating current to the average current I is called the form factor and expressed in Kf. For full-wave rectification Kf=1.11, for half-wave rectification Kf=2.22.
In fact, the AC voltage measurement circuit of the multimeter mostly adopts the half-wave current reporting method. As shown in Figure 2-5. As can be seen from the figure, when the measured AC voltage is in the positive half cycle, the half-wave rectifying current flows through the positive terminal, multiplier resistors R3, R2, R1, Z1, and flows through the ammeter head to the negative terminal. When the measured AC voltage is in the negative half cycle, z1 is turned off, no current flows through the meter, and the rectified current flows out from the positive terminal through z2, R1, R2, and R3. The rectifier in the multimeter generally uses a semiconductor rectifier. There are generally two methods for measuring AC voltage. One is to share a set of multiplier resistances when measuring AC and DC voltages, and draw a scale line on the dial.
