The measurement principle of mechanical pointer type multimeter
"Multimeter" is the abbreviation of a multimeter, which is an essential tool in our production. A multimeter can measure current, voltage, resistance, and some can also measure amplification factors such as frequency, capacity, logical potential, decibel value, etc. There are many types of multimeters, and now there are mechanical pointer and digital multimeters. They each have their own advantages and disadvantages; For beginners in electronics, it is recommended to use a pointer type multimeter as it is helpful for us to familiarize ourselves with some electronic knowledge principles. The following mainly introduces the measurement principle of a mechanical pointer type multimeter.
The basic principle of this type of multimeter is to use a sensitive magneto electric direct current meter (microampere meter) as the meter head. When a small current passes through the meter head, there will be a current indication. But the meter head cannot pass through large currents, so some resistors must be connected in parallel or series on the meter head for shunt or voltage reduction, in order to measure the current, voltage, and resistance in the circuit. Below are the introductions.
1. Principle of measuring DC current.
By connecting an appropriate resistor (called a shunt resistor) in parallel on the meter head for shunt, the current range can be extended. By changing the resistance value of the shunt resistor, the current measurement range can be changed.
2. Principle of measuring DC voltage.
By connecting an appropriate resistor (called a multiplier resistor) in series on the meter head for voltage reduction, the voltage range can be extended. By changing the resistance value of the doubling resistor, the measurement range of voltage can be changed.
Principle of measuring AC voltage.
Because the meter head is a DC meter, a parallel or series half wave rectifier circuit needs to be installed when measuring AC, which rectifies the AC to DC and then passes through the meter head. This way, the AC voltage can be measured based on the magnitude of the DC current. The method of expanding the range of AC voltage is similar to that of DC voltage.
4. Principle of measuring resistance.
Connect appropriate resistors in parallel or series on the meter head, and connect a battery in series to allow current to pass through the measured resistor. Based on the magnitude of the current, the resistance value can be measured. By changing the resistance value of the shunt resistor, the range of the resistor can be changed.
