The important structural components of a multimeter:
1. Header:
The head of a multimeter is a sensitive ammeter. The dial on the meter head is printed with various symbols, scale lines, and numerical values.
The symbol A - V - Ω indicates that this electric meter is a multimeter that can measure current, voltage, and resistance. There are multiple scale lines printed on the dial, among which the resistance scale line marked with "Ω" on the right end is zero, and the left end is ∞. The distribution of scale values is uneven.
The symbol "-" or "DC" represents direct current, "~" or "AC" represents alternating current, and "~" represents the common scale line between alternating current and direct current. The lines below the scale line represent the scale values corresponding to the different gear positions of the selector switch.
There is also a mechanical zero adjustment knob on the meter head to calibrate the pointer to the left zero position.
2. Select switch:
The selection switch of the multimeter is a multi gear rotary switch. Used to select measurement items and ranges. General multimeter measurement items include: "mA"; DC current, "V (-)": DC voltage, "V (~)": AC voltage, "Ω": resistance. Each measurement item is divided into several different ranges for selection.
3. Pen and pen socket:
The pen is divided into two parts: red and black. When using, the red probe should be inserted into the socket marked with a "+" sign, and the black probe should be inserted into the socket marked with a "-" sign.
4. Header (pointer type):
It is a highly sensitive magneto electric DC ammeter, and the main performance indicators of a multimeter depend largely on the performance of the meter head. The sensitivity of the meter head refers to the value of the direct current flowing through the meter head when the pointer deviates to full scale. The smaller this value, the higher the sensitivity of the meter head. The larger the internal resistance during voltage measurement, the better its performance.
There are four scale lines on the header, and their functions are as follows:
The first line (from top to bottom) is marked with R or Ω, indicating the resistance value. When the switch is in the ohm range, this scale line is read.
The second line is marked with ∽ and VA, indicating the values of AC and DC voltage and DC current. When the conversion switch is in the AC or DC voltage or DC current mode and the range is in other positions except for AC 10V, this scale line is read.
The third line is marked with 10V, indicating the AC voltage value of 10V. When the conversion switch is in the AC/DC voltage range and the measuring range is at 10V AC, this scale line is read.
The fourth item is marked with dB, indicating the audio level.
5. Header (digital):
The header of a digital multimeter is generally composed of an A/D (analog/digital) conversion chip, peripheral components, and a liquid crystal display. The accuracy of a multimeter is affected by the header. A multimeter, due to the number converted by the A/D chip, is also commonly referred to as a 3 1/2 digit digital multimeter, 4 1/2 digit digital multimeter, and so on.
The most commonly used chips are ICL7106 (a classic 3-bit and a half LCD manual range chip, later versions include 7106A, 7106B, 72067240, etc.), ICL7129 (a classic 4-bit and a half LCD manual range chip), and ICL7107 (a classic 3-bit and a half LED manual range chip).
6. Measurement line:
Measurement circuit is a circuit used to convert various measured signals into small DC currents suitable for meter measurement. It consists of resistors, semiconductor components, and batteries
It can convert various types of measurements (such as current, voltage, resistance, etc.) and different ranges into a certain limit of small DC current through a series of processing (such as rectification, diversion, voltage division, etc.) and send it to the meter for measurement.
7. Conversion switch:
Its function is to select various measurement circuits to meet the measurement requirements of different types and ranges. A toggle switch is usually a circular dial with functions and ranges marked around it.
