Introduction to common types of multimeters

1. Introduction

Multimeters are also called multiplex meters, multimeters, three-meters, multi-meters, etc. They are a multi-function, multi-range measuring instrument that is indispensable in power electronics and other sectors. Generally, it is mainly used to measure voltage, current and resistance.

Second, the classification of multimeters

Divided by display method

1. Analog 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. Medium/digital multimeter

4. Digital/analog hybrid instrument

5. Digital/analog dual display instrument

6. Multipurpose oscilloscope (combining the kinetic energy of digital multimeter, digital storage oscilloscope, etc.).

Three, the structure of the multimeter

1. Header

1) Pointer meter

It is a high-sensitivity magnetoelectric DC current meter. 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 value of the DC current flowing through the meter head when the pointer of the meter head is fully deflection, the smaller the value, the higher the sensitivity of the meter head. The greater the internal resistance when measuring voltage, the better its performance. There are four tick marks on the header, and their functions are as follows:

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

The second line is marked with ∽ and VA, which indicate the values of AC and DC voltage and DC current. When the switch is in AC, DC voltage or DC current, and the range is in other positions except AC 10V, this scale is read line.

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

The fourth bar is marked with dB, which 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 + a liquid crystal display. The accuracy of the multimeter is affected by the meter head. The multimeter is generally called due to the number converted from the A/D chip For 3 1/2 digit multimeter, 4 1/2 digit multimeter and so on. Commonly used chips are ICL7106 (3 and a half LCD manual range classic chip, subsequent versions are 7106A, 7106B, 7206, 7240, etc.), ICL7129 (4 and a half LCD manual range classic chip), ICL7107 (3 and a half LED manual range classic chip chip).

2. Measuring circuit

The measurement circuit is a circuit used to convert all kinds of measured to a small DC current suitable for meter measurement. It is composed of resistance, semiconductor components and batteries. It can measure various kinds of measured (such as current, voltage, resistance, etc.) , Different measuring ranges, after a series of treatments (such as rectification, shunting, voltage division, etc.), uniformly turn into a certain limit of small DC current and send it to the meter for measurement.

3. Transfer switch

Its function is to select a variety of different measurement circuits to meet the measurement requirements of different types and different ranges. There are generally two transfer switches, which are marked with different gear positions and ranges respectively.

4. Test lead and test lead socket

The test leads are divided into red and black. When in use, insert the red test lead into the jack marked with "+" and the black test lead into the jack marked with "-".

Multimeter symbol meaning

1. ∽ means alternating current, - means direct current.

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

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

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

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

Multimeter principle

The basic principle of a multimeter is to use a sensitive magnetoelectric DC ammeter (micro-ammeter) as the meter head. When a small current passes through the meter, there will be a current indication. However, the meter head cannot pass large currents, so some resistors in parallel and series must be connected to the meter head to shunt or step down, so as to measure the current, voltage and resistance in the circuit.