The Principle and Standards of Multimeter on/off Range
On/off range is a measurement mode that almost all multimeters have, used to measure the continuity (short circuit) of a circuit. Generally, it will be combined with a buzzer and an LED light. The buzzer will sound or the LED light will light up, indicating that the circuit is conductive. As shown in the figure, the symbol in the red box represents the on/off range of the multimeter.
On/off gear principle
When the multimeter is set to the on/off position, the internal circuit that is connected is: the black lead is connected to the negative pole of the internal battery, the positive pole of the battery is connected to a resistance with a small resistance value, and the other end of the resistance is connected to a red lead. The internal beeping circuit obtains a trigger signal from the resistor. If the two probes are short circuited or the resistance between them is small, then the voltage on the triggering resistor in the meter is higher, triggering a beep. If the resistance between two probes is large, then the partial voltage of the internal triggering resistor in series is small and cannot trigger the beep.
On/off gear standard
The general definition is that 80 ohms or less is conduction, otherwise it is non conduction. That is to say, connect the red and black probes of the multimeter on both sides of a circuit. If the resistance value of this circuit is less than 80 ohms, the multimeter will make a sound and believe that this circuit is conductive.
What is the difference between a megohmmeter and a multimeter?
1. Different composition structures:
A megohmmeter consists of medium to large scale integrated circuits. This meter has a high output power, high short-circuit current value, and multiple output voltage levels (each model has four voltage levels).
The multimeter consists of three main parts: the meter head, measuring circuit, and conversion switch.
2. The working principle is different:
A megohmmeter uses a voltage to excite the device or network under test, and then measures the current generated by the excitation, using Ohm's law to measure the resistance.
The basic principle of a multimeter is to use a sensitive magnetoelectric direct current meter (microampere meter) as the meter head. When a small current passes through the meter head, there will be a current indication.
3. Different scope of use:
Megohmmeter is a commonly used and essential instrument for industrial enterprises in 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.
A multimeter can not only be used to measure the resistance of the object being measured, but also to measure AC and DC voltage. Some multimeters can even measure the main parameters of transistors and the capacitance of capacitors.
