The on-off multimeter gear's basic operation and standards
The on-off position is a measurement mode that almost all multimeters have, and is used to measure whether the line is on or off (short circuit). Generally, a buzzer and an LED light are used. The buzzer sounds or the LED light turns on, indicating that the circuit is connected. As shown in the figure, the sign in the red box is the on-off gear of the multimeter.
On-off gear principle
When the multimeter is turned to the on-off position, the internal circuit that is connected is: the black test lead is connected to the negative pole of the internal battery, the positive pole of the battery is connected to a resistor with a small resistance, and the other end of the resistor is connected to the red test lead. The internal chirping circuit gets the trigger signal from the resistor. If the two test leads are short-circuited or the resistance between them is small, then the voltage on the trigger resistor inside the meter is high, thus triggering the beep. If the resistance between the two test leads is large, then the divided voltage of the internal trigger resistor connected in series is very small, and the beep cannot be triggered.
On-off gear standard
The general definition is that 80 ohms and below are conduction, otherwise it is non-conduction. That is to say, connect the red and black test leads of the multimeter to both sides of a line. If the resistance of this line is lower than 80 ohms, the multimeter will make a sound and think that this line is conducting.
