The Structure of a Multimeter, the Meanings of Various Symbols and Its Usage Method
A multimeter is mainly composed of three parts: the meter head, the measuring circuit, and the changeover switch.
Meter Head
It is a high-sensitivity magnetoelectric DC ammeter. The main performance indicators of the multimeter basically depend on the performance of the meter head. The sensitivity of the meter head refers to the value of the DC current flowing through the meter head when the pointer of the meter head deflects to the full scale. The smaller this value is, the higher the sensitivity of the meter head. When measuring voltage, the larger the internal resistance, the better the performance. There are four scale lines on the meter head, and their functions are as follows: The first one (from top to bottom) is marked with R or Ω, indicating the resistance value. When the changeover switch is in the ohm range, this scale line is read. The second one is marked with ∽ and VA, indicating the AC and DC voltage values and the DC current value. When the changeover switch is in the AC or DC voltage range or the DC current range, and the range is in any position other than the AC 10V range, this scale line is read. The third one is marked with 10V, indicating the AC voltage value of 10V. When the changeover switch is in the AC or DC voltage range and the range is set to AC 10V, this scale line is read. The fourth one is marked with dB, indicating the audio level.
Measuring Circuit
The measuring circuit is a circuit used to convert various measured quantities into a small DC current suitable for measurement by the meter head. It is composed of resistors, semiconductor components, and batteries.
It can convert various different measured quantities (such as current, voltage, resistance, etc.) and different ranges into a small DC current within a certain range through a series of processes (such as rectification, shunting, voltage division, etc.) and send it to the meter head for measurement.
Changeover Switch
Its function is to select various different measuring circuits to meet the measurement requirements of different types and ranges. Generally, there are two changeover switches, which are respectively marked with different gears and ranges.
