Introduction to the Composition and Structure of a Multimeter
The basic principle of a multimeter is to use a sensitive magnetoelectric DC Ammeter (microammeter) 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 with the meter head for shunt or voltage reduction, so as to measure the current, voltage and resistance in the circuit.
The composition and structure of a multimeter
1、 Meter header
1. Pointer type meter is a highly sensitive magnetoelectric DC Ammeter, and 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 direct current value that flows through the meter head when the pointer is deflected at full scale. The smaller this value, the higher the sensitivity of the meter head. The greater the internal resistance during voltage measurement, the better its performance. There are four tick marks 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 transfer switch is in the ohm gear, this scale line is read; ② The second line is marked with Δ and VA, indicating the AC/DC voltage and DC current values. When the transfer switch is in the AC/DC voltage or DC current range, 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 transfer switch is in the AC/DC voltage range and the AC range is 10V, read this scale line; ④ The fourth item is marked with dB, indicating the audio level. 2. The head of a digital multimeter is generally composed of an A/D (analog/digital) conversion chip, peripheral components, and LCD display. The accuracy of a multimeter is affected by the head. Due to the numbers converted by the A/D chip, a multimeter is commonly referred to as a 31/2 digit digital multimeter, a 41/2 digit digital multimeter, and so on. The commonly used chips are ICL7106 (3 and a half LCD manual range classic chip, with subsequent versions of 7106A, 7106B, 7206, 7240, etc.), ICL7129 (4 and a half LCD manual range classic chip), and ICL7107 (3 and a half LED manual range classic chip).
2、 The measurement circuit is a circuit used to convert various measurements into small DC currents suitable for measurement by the meter head. It is composed of resistors, semiconductor components, and batteries. It can convert various measurements (such as current, voltage, resistance, etc.), different ranges, and through a series of processing (such as rectification, shunt, voltage sharing, etc.) into a certain limit of small DC currents and send them to the meter head for measurement.
3、 The function of a transfer switch is to select various measurement circuits to meet the measurement requirements of different types and ranges. There are generally two transfer 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 "+", and the black probe should be inserted into the socket marked with "-".
