Should a multimeter measure voltage in AC mode in series or in parallel?
The multimeter measures voltage in parallel and measures current in series. This is true whether it is AC or DC. The internal resistance of the voltage range of the multimeter is close to infinity, so if you choose the voltage range and connect the multimeter in series in the circuit, there will actually be no current in the circuit or It is said that the current is very small, so no data can be measured. For the current range, the internal resistance is close to 0, so connecting it in series in the circuit will not affect the operation of subsequent electrical appliances.
However, if the wrong current level is selected and connected in parallel in the circuit, such as the situation asked by the question, if the voltage level is changed to the current level and connected in parallel at both ends of the 220V power supply, this is quite dangerous. A direct short circuit may occur, and the multimeter or The lines are all burned out.
The voltage level is relatively safe to measure. Even if it is connected in series in a circuit, it will not be as harmful as if the current level is connected incorrectly. We use a multimeter to measure some data, so we must think about how to do it before measuring. Measurement.
Whether it is connected in series or in parallel, we must first understand the principle of measuring AC voltage with a multimeter. The multimeter head can only pass DC voltage, that is, it can only measure DC voltage. So why can it measure AC voltage? That is because there is a rectifier circuit inside the multimeter. Using The unidirectional conductivity of the diode changes the AC signal into a DC signal, so the AC voltage can be measured. In other words, the AC setting of the multimeter measures the 220V household voltage, which is a parallel circuit.
Principle of AC voltage measurement: When a multimeter measures AC voltage, there is a half-wave rectifier circuit inside the multimeter. When the AC voltage is to be measured, the AC voltage is rectified into DC voltage and then passes through two meters. Finally, according to the DC voltage The AC voltage is measured by the magnitude of the AC voltage, and the AC voltage displayed by the multimeter is not the instantaneous value of the AC current, but the average value over a period of time, that is, the effective value. In fact, the inside of a multimeter is not just that simple. It also amplifies the signal through an operational amplifier, performs analog-to-digital conversion after sampling, and the final result is displayed on the screen.
When measuring the 220V voltage at home, you only need to select the AC range. The following is a Fluke digital multimeter. Insert the black and red test leads into the corresponding positions and directly connect them to the zero live wire of the mains. There is no need to distinguish which one is the live wire and which one is the neutral wire. , the voltage can be read directly
