Principle of operation of the resistance of a multimeter
The working principle of the multimeter resistance gear uses a sensitive magneto-electric DC ammeter (microammeter) as a meter head. When a small current passes through the head, there will be a current indication. However, the head cannot pass large currents, so some resistors must be connected in parallel and in series to shunt or step down the current, voltage and resistance in the circuit.
Because the head is a DC meter, so when measuring AC, you need to add a parallel and series half-wave rectifier circuit to rectify the AC into DC and then through the head, so you can measure the AC voltage according to the size of the DC. The method of extending the AC voltage range is similar to the DC voltage range.
Connect appropriate resistors in parallel and series on the meter head, and connect a battery in series at the same time, so that the current passes through the measured resistor, and according to the size of the current, the resistance value can be measured. By changing the resistance of the shunt resistor, the range of the resistance can be changed.
Extended Information
Multimeter is a relatively precise instrument, if not used properly, it will cause inaccurate measurements and very easy to damage. However, as long as you know how to use the multimeter and the precautions, be careful, then the multimeter can be durable.
The use of multimeter should pay attention to the following matters:
1. Measurement of current and voltage should not be rotated in the wrong gear. If the wrong resistance or current gear to measure the voltage, it is very easy to burn the meter. When the multimeter is not in use, it is better to rotate the gear to the highest level of AC voltage to avoid damage due to improper use.
2. When measuring DC voltage and DC current, pay attention to the polarity of "+" and "-" and do not connect the wrong one. If you find the pointer on the reverse, both should be immediately switched to the table bar, so as not to damage the pointer and the head.
3. If you don't know the size of the measured voltage or current, you should use the highest grade first, and then choose a suitable grade to test, so as to avoid excessive deflection of the needle and damage to the meter head. The closer the selected gear is to the measured value, the more accurate the measured value will be.
