The structure of the digital multimeter
1. Header
The head of the multimeter is a sensitive galvanometer. The dial on the head is printed with a variety of symbols, tick marks and numerical values.
The symbol A-V-Ω indicates that this meter is a multimeter that can measure current, voltage and resistance.
There are multiple scale lines printed on the dial. The resistance scale line marked with "Ω" on the right end is zero on the right end and ∞ on the left end. The distribution of scale values is uneven.
The symbol "-" or "DC" means direct current, "～" or "AC" means alternating current, and "～" means the scale line shared by alternating current and direct current.
The lines of numbers under the scale line are the scale values corresponding to the different positions of the selector switch. There is also a mechanical zero adjustment knob on the head to correct the zero position of the pointer at the left end.
Digital:
The head of the digital multimeter is generally composed of an A/D (analog/digital) conversion chip + peripheral components + liquid crystal display. The accuracy of the multimeter is affected by the head. For 3 1/2 digit DMM, 4 1/2 digit DMM and so on. The most commonly used chips are ICL7106 (3 and a half-digit LCD manual range classic chip, subsequent versions are 7106A, 7106B, 7206, 7240, etc.), ICL7129 (4 and a half-digit LCD manual range classic chip), ICL7107 (3 and a half-digit LED manual range) classic chips).
2. Measurement circuit
The measurement circuit is a circuit used to convert various measurands into tiny DC currents suitable for meter measurement. It consists of resistors, semiconductor components and batteries.
It can convert various measurands (such as current, voltage, resistance, etc.) and different ranges, and after a series of processing (such as rectification, shunt, voltage division, etc.) head to measure.
3. Transfer switch
Generally speaking, the function of the switch is to select various measurement lines to meet the measurement requirements of different types and ranges. The transfer switch is generally a circular dial with functions and ranges marked around it.
