Principles and standards of on-off gears for multimeters
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.
What is the difference between a megohmmeter and a multimeter?
1. Different composition structures:
A megohmmeter is composed of medium to large scale integrated circuits. This table has high output power, high short-circuit current value, and multiple output voltage levels (each model has four voltage levels).
2. The working principle is different:
A megohmmeter measures resistance by exciting the device or network under test with a voltage, and then measuring the current generated by the excitation using Ohm's law.
The basic principle of a multimeter is to use a sensitive magneto electric DC ammeter (microampere meter) as the meter head. When a small current passes through the meter, there will be a current indication.
3. Different usage ranges:
A megohmmeter is a commonly used and essential instrument in industrial sectors such as power, postal and telecommunications, communication, electromechanical installation and maintenance, as well as the use of electricity as industrial power or energy. It is suitable for measuring the resistance values of various insulation materials and the insulation resistance of transformers, motors, cables, and electrical equipment.
