Classification and Composition of Multimeters

Classification of Multimeters

1. Classification by Meter Head Structure

According to the structure of the working meter head, multimeters can be divided intoMechanical (pointer)multimeters andDigital display type(shortened to digital type) multimeters.

2. Classification by Functional Operation Knob

According to the functional operation knob, multimeters can be divided into single-knob multimeters and double-knob multimeters.

3. Classification by Measurement Function

According to the measurement function, multimeters can be divided intoOrdinary typemultimeters andMultifunctional typemultimeters.

Ordinary multimeters can only measure resistance, voltage, and current, so they are also called three-use meters, and the measured current capacity is relatively small.

Early multifunctional multimeters only added the transistor amplification gain measurement function and large current measurement function. Later-produced multifunctional multimeters also added short-circuit (continuity) test function and capacitance measurement function. Some multimeters even added undervoltage (battery low power) prompts, automatic delay shutdown, audio level, temperature, inductance, frequency measurement, and remote control signal detection functions. The protection functions of multifunctional multimeters are also becoming increasingly perfect (most of the multimeters are multifunctional, and can perform data communication, single-channel oscilloscope, intelligent screening, etc.).

Composition of Multimeters

1. Composition of Pointer Multimeters

Pointer multimeters consist of a magnetic electric meter head, a function knob, a zero adjustment knob, jacks, test leads, and an outer casing.

(1) Meter Head

The meter head consists of a magnet, a coil, a spiral spring, and a pointer. When a weak current passes through the coil, it will generate a magnetic field, driving the pointer to deflect from the left to the right. The greater the current, the greater the deflection angle. Because the coil is made of thin enameled wire, it needs to be powered by voltage reduction and current limiting to obtain a larger range and more measurement items.

(2) Dial

The dial has various graphics, symbols, and multiple scales.

The first scale is the resistance reading. Its right end is "0", and the left end is "infinity (∞)", so the reading should be read from right to left, which means that the closer the pointer is to the right end, the smaller the value.

The second scale is the reading of AC and DC voltage and DC current. Its left end is "0", and the right end is the maximum value, so the reading should be read from left to right, which means that the closer the pointer is to the right end, the greater the value.

The third scale is set to improve the reading accuracy of 0-10V AC voltage. Its left end is "0", and its right end is the maximum value, so the reading should be read from left to right. That is, the closer the pointer is to the right end, the greater the value.

The fourth scale is the decibel reading. Its left end is "-10dB", and its right end is "+22dB". So the reading should be read from left to right, that is, the closer the pointer is to the right end, the greater the value.

2. Composition of Digital Multimeters

Digital multimeters are mainly composed of two parts:

The first part isInput and conversion partIts main function is to convert various measured quantities into DC voltage through current/voltage converter (I/U converter), AC/DC converter (AC/DC converter), and resistance/voltage converter (R/U converter), and then through range selection, it is amplified or attenuated and sent to the analog/digital converter (A/D converter) for conversion and processing:

The second part isA/D conversion circuit, decoding circuit, and display partIts structure and function are the same as those of a DC digital voltmeter. Therefore, a digital multimeter uses a DC digital voltmeter as the basic meter, and with a DC voltage, AC voltage, current, and resistance converter that has a linear relationship with it, it can accurately display the corresponding electrical parameters in digital form.

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