Fluke low-power digital multimeter internal circuit disassembly
Multimeters, also known as multiplex meters, multimeters, triple meters, multimeters, etc., are indispensable measuring instruments in power electronics and other departments. Generally, the main purpose is to measure voltage, current and resistance. Multimeters are divided into pointer multimeters and digital multimeters according to the display mode. It is a multi-function and multi-range measuring instrument. Generally, a multimeter can measure DC current, DC voltage, AC current, AC voltage, resistance and audio level, etc., and some can also measure AC current, capacitance, inductance and semiconductor. Some parameters (like β) etc.
The appearance of the multimeter:
The function of measuring voltage, current and resistance of the multimeter is realized by the conversion circuit part, and the measurement of current and resistance is based on the measurement of voltage, that is to say, the digital multimeter is extended on the basis of the digital DC voltmeter.
Disassembly of the multimeter
The internal structure of the multimeter
Small switching power supply transformers, crystal oscillators, and management chips for switching power supplies
Fluke's own chips
The digital multimeter uses a variety of oscillation, amplification, frequency division protection and other circuits, so it has many functions. For example, it can measure temperature, frequency (in a lower range), capacitance, inductance, be a signal generator and so on.
The handheld digital multimeter uses a single-chip A/D converter, and the peripheral circuit is relatively simple, requiring only a small number of auxiliary chips and components. With the continuous advent of dedicated chips for single-chip digital multimeters, a relatively complete automatic range digital multimeter can be formed by using one IC, creating favorable conditions for simplifying design and reducing costs.
New digital multimeters generally use CMOS large-scale integrated circuit A/D converters, and the power consumption of the whole machine is very low.
Write at the end:
The basic principle of the multimeter is to use a sensitive magnetoelectric DC ammeter (microammeter) as the head. Multimeter When a tiny current passes through the meter, 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 on the meter head for shunt or step-down, so as to measure the current, voltage and resistance in the circuit.
In the measurement process of the digital multimeter, the conversion circuit converts the measured value into a DC voltage signal, and the multimeter converts the voltage analog value into a digital value by an analog-to-digital (A/D) converter, and then counts through an electronic counter, and finally uses the measurement result. The numbers are shown directly on the display. The function of measuring voltage, current and resistance of the multimeter is realized by the conversion circuit part, and the measurement of current and resistance is based on the measurement of voltage, that is to say, the digital multimeter is extended on the basis of the digital DC voltmeter. The digital DC voltmeter A/D converter converts the analog voltage that changes continuously with time into a digital quantity, and then counts the digital quantity by an electronic counter to obtain the measurement result, and then the decoding display circuit displays the measurement result. The logic control circuit controls the coordination of the circuit, and completes the entire measurement process in sequence under the action of the clock
