Components and Structure of the Multimeter
The basic principle of a multimeter is to use a sensitive magneto electric DC ammeter (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 a large current. Therefore, some resistors must be connected in parallel or in series on the meter head for shunt or voltage reduction, in order to measure the current, voltage, and resistance in the circuit. The composition structure of a multimeter is as follows: 1. Meter head
1. Pointer meter head. It is a highly sensitive magneto electric DC ammeter, and the main performance indicators of a multimeter basically depend 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, and the greater the internal resistance during voltage measurement, resulting in better performance. There are four scale lines on the meter head, and their functions are as follows:
① 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;
② The second line is marked with ∽ and VA, indicating the values of AC/DC voltage and DC current. When the conversion switch is in the AC/DC voltage or DC current mode and the range is in other positions except for AC 10V, this scale line is read;
③ 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; ④ The fourth item is marked with dB, indicating the audio level.
2. 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 generally also known as a 31/2-digit digital multimeter, 41/2-digit digital multimeter, and so on. The commonly used chips are ICL7106 (a classic 3-bit and a half LCD manual range chip, later versions include 7106A, 7106B, 7206, 7240, 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).
2, Measurement circuit is a circuit used to convert various measured signals into small DC currents suitable for meter head measurement. It consists of resistors, semiconductor components, and batteries. It can unify various measured signals (such as current, voltage, resistance, etc.) and different ranges through a series of processes (such as rectification, diversion, voltage division, etc.) into a certain limit of small DC currents and send them to the meter head for measurement.
3, The function of the conversion switch is to select various measurement circuits to meet the measurement requirements of different types and ranges. There are generally two conversion switches, each marked with different gears and ranges.
4, The probe and probe socket are divided into two types: 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.
