The principle and standard of multimeter on and off
The on-off mode is a measurement mode that almost all multimeters have, used to measure the continuity (short circuit) of a circuit. It is usually paired with a buzzer and LED light. When the buzzer makes a sound or the LED light is on, it indicates that the circuit is conductive. As shown in the figure, the symbol inside the red box is the on/off range of the multimeter.
Principle of on-off mode
When the multimeter is turned to the on/off position, the internal circuit that is connected is: the black probe is connected to the negative terminal of the internal battery, the positive terminal of the battery is connected to a resistor with a very low resistance value, and the other end of the resistor is connected to the red probe. The internal beep circuit obtains the trigger signal from the resistor. If two probes are short circuited or the resistance between them is small, the voltage on the trigger resistor inside the meter will be higher, triggering a beep. If the resistance between two probes is high, the voltage division of the internal trigger resistor in series will be small, and it will not trigger the beep.
Standard for on-off mode
The general definition is that 80 ohms or less is conductive, otherwise it is non-conductive. That is to say, connect the red and black probes of the multimeter to both sides of a circuit. If the resistance of this circuit is less than 80 ohms, the multimeter will make a sound and consider this circuit to be conductive.
