Introduction to Common Types of Multimeters

1. Introduction to Multimeter

A multimeter, also known as a multiplexer, multi-meter, three-meter, complex meter, etc., is an indispensable multi-functional, multi-range measuring instrument in the power electronics and other departments. Its main purpose is generally to measure voltage, current and resistance.

2. Multimeter Classification

According to the display mode

1. Pointer multimeter

2. Digital multimeter

Classification of digital multimeters

According to the range conversion method

1. Manual range (MAN RANGZ)

2. Automatic range (AUTO RANGZ)

3. Automatic/manual range (AUTO/MAN RANGZ).

According to function, purpose and price, it can be divided into

1. Low-end digital multimeter (also known as popular digital multimeter)

2. Mid-range digital multimeter

3. Mid/high-end digital multimeter

4. Digital/analog hybrid instrument

5. Instrument with dual digital/analog display

6. Multi-purpose oscilloscope (integrates the functions of digital multimeter, digital storage oscilloscope, etc.)

3. Multimeter structure

1. Table header

1) Pointer type meter

It is a highly sensitive magnetoelectric DC ammeter. The main performance indicators of the multimeter basically depend on the performance of the meter. The sensitivity of the meter refers to the DC current value flowing through the meter when the meter pointer is fully deflected. The smaller this value is, the higher the sensitivity of the meter. The greater the internal resistance when measuring voltage, the better its performance. There are four scale lines on the meter, and their functions are as follows:

The first line (from top to bottom) is marked with R or Ω, which indicates the resistance value. When the conversion switch is in the ohm position, read this scale line.

The second line is marked with ∽ and VA, indicating the AC and DC voltage and DC current values. When the conversion switch is in the AC, DC voltage or DC current position and the range is in a position other than AC 10V, read this scale line.

The third line is marked with 10V, which indicates the AC voltage value of 10V. When the conversion switch is in the AC/DC voltage position and the range is AC 10V, read this scale line.

The fourth bar is marked in dB and indicates the audio level.

2) Digital meter

The meter head of a digital multimeter is generally composed of an A/D (analog/digital) conversion chip + peripheral components + LCD display. The accuracy of the multimeter is affected by the meter head. Due to the numbers converted by the A/D chip, the multimeter is generally also called a 3 1/2-digit digital multimeter, a 4 1/2-digit digital multimeter, etc. The most commonly used chips are ICL7106 (3.5-digit LCD manual range classic chip, subsequent versions are 7106A, 7106B, 7206, 7240, etc.), ICL7129 (4.5-digit LCD manual range classic chip), and ICL7107 (3.5-digit LED manual range classic chip).

2. Measurement circuit

The measuring circuit is a circuit used to convert various measured quantities into tiny DC currents suitable for measurement by the meter. 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 tiny DC currents of a certain limit through a series of processing (such as rectification, shunting, voltage division, etc.) and send them to the meter for measurement.

3. Switch

Its function 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. Test leads and test lead jacks

The test leads are divided into red and black. When using, the red test lead should be inserted into the jack marked with "+" and the black test lead should be inserted into the jack marked with "-".

Meaning of multimeter symbols

1. ∽ indicates alternating current, and -- indicates direct current.

2. V-2.5KV 4000Ω/V means that for AC voltage and 2.5KV DC voltage range, its sensitivity is 4000Ω/V.

3. A-V-Ω means that current, voltage and resistance can be measured.

4. 45-65-1000Hz means the operating frequency range is below 1000Hz, and the standard operating frequency range is 45-65Hz.

5. 2000Ω/V DC means the sensitivity of DC range is 2000Ω/V.

Multimeter Principle

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. However, the meter head cannot pass a large current, so some resistors must be connected in parallel or in series to the meter head for shunting or voltage reduction, so as to measure the current, voltage and resistance in the circuit.