Classification and operation instructions of digital multimeters
Classification of digital multimeters
Digital multimeters are classified according to the range conversion method and can be divided into three types: manual range (MAN RANGZ), automatic range (AUTO RANGZ), and automatic/manual range (AUTO/MAN RANGZ).
According to different functions, uses and prices, digital multimeters can be roughly divided into 9 categories:
Low-end digital multimeters (also known as popular digital multimeters), mid-range digital multimeters, medium/digital multimeters, digital/analog hybrid meters, digital/analog dual display meters, multipurpose oscilloscopes (digital multimeters, digital storage oscilloscope and other kinetic energy in one).
Digital multimeter test function
The digital multimeter can not only measure DC voltage (DCV), AC voltage (ACV), DC current (DCA), AC current (ACA), resistance (Ω), diode forward voltage drop (VF), and transistor emitter current amplification coefficient ( hrg), it can also measure capacitance (C), conductance (ns), temperature (T), frequency (f), and adds a buzzer level (BZ) for checking line continuity and low-power method for measuring resistance. gear (L0Ω). Some instruments also have automatic conversion functions for inductance gear, signal gear, AC/DC, and automatic range conversion for capacitance gear.
Most digital digital multimeters have added the following novel and practical test functions: reading hold (HOLD), logic test (LOGIC), true effective value (TRMS), relative value measurement (RELΔ), automatic shutdown (AUTO OFF POWER), etc.
Anti-interference ability of digital multimeter
Simple digital multimeters generally use the integral A/D conversion principle.
As long as the forward integration time is chosen to be exactly equal to an integral multiple of the cross-frame interference signal period, the cross-frame interference can be effectively suppressed. This is because the cross-frame interference signal is averaged out during the forward integration stage. The common frame rejection ratio (CMRR) of mid- and low-end digital multimeters can reach 86 to 120dB.
Development Trends of Digital Multimeters
Integration: The handheld digital multimeter uses a single-chip A/D converter, and the peripheral circuit is relatively simple, requiring only a few auxiliary chips and components. With the continuous advent of single-chip digital multimeter dedicated chips, a relatively complete automatic range digital multimeter can be constructed using one IC, creating favorable conditions for simplifying design and reducing costs.
Low power consumption: New digital multimeters generally use CMOS large-scale integrated circuit A/D converters, and the overall power consumption is very low.
Comparison of the advantages and disadvantages of ordinary multimeters and digital multimeters:
Analog and digital multimeters each have their own advantages and disadvantages.
The analog multimeter is an average meter with an intuitive and vivid reading indication. (Generally, the reading value is closely related to the pointer swing angle, so it is very intuitive).
A digital multimeter is an instantaneous instrument. It takes 0.3 seconds to take
One sample is used to display the measurement results. Sometimes the results of each sampling are only very similar but not exactly the same. This is not as convenient as the pointer type for reading the results. Pointer multimeters generally do not have an amplifier inside, so the internal resistance is small.
Because the digital multimeter uses an operational amplifier circuit inside, the internal resistance can be made very large, often 1M ohm or more. (i.e. higher sensitivity can be obtained). This makes the impact on the circuit under test smaller and the measurement accuracy higher.
Because the internal resistance of the pointer multimeter is small, discrete components are often used to form a shunt and voltage divider circuit. Therefore, the frequency characteristics are uneven (relative to digital), and the frequency characteristics of digital multimeters are relatively better. The internal structure of the analog multimeter is simple, so it has lower cost, fewer functions, simple maintenance, and strong overcurrent and overvoltage capabilities.
The digital multimeter uses a variety of oscillation, amplification, frequency division protection and other circuits internally, so it has many functions. For example, it can measure temperature, frequency (in a lower range), capacitance, inductance, make a signal generator, etc.
Because the internal structure of digital multimeters uses integrated circuits, they have poor overload capabilities and are generally not easy to repair after damage. Digital multimeters have low output voltages (usually no more than 1 volt). It is inconvenient to test some components with special voltage characteristics (such as thyristors, light-emitting diodes, etc.). The output voltage of the analog multimeter is higher. The current is also large, making it easy to test thyristors, light-emitting diodes, etc.
Beginners should use an analog multimeter, and non-beginners should use both instruments.
