measurement approach and multimeter's AC frequency response
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), transistor emitter current amplification factor ( hrg), can also measure capacitance (C), conductance (ns), temperature (T), frequency (f), and added a buzzer file (BZ) for checking the continuity of the line, low power method to measure resistance file (L0Ω). Some instruments also have inductance gear, signal gear, AC/DC automatic conversion function, and capacitance gear automatic range conversion function.
Generally speaking, the measurement method of the multimeter is mainly for the measurement of AC signals. We all know that there are many types of AC signals and various complex situations, and with the change of the frequency of the AC signal, various frequency responses appear, which affect the measurement of the multimeter. There are generally two methods for multimeters to measure AC signals: average value and true RMS measurement. Average value measurement is generally for pure sine waves, it uses the method of estimating and averaging to measure AC signals, but for non-sine wave signals, there will be a large error.
At the same time, if the sine wave signal has harmonic interference, its measurement error will also change greatly, and the true RMS measurement is to calculate the current and voltage by multiplying the instantaneous peak value of the waveform by 0.707 to ensure that the distortion and noise system Accurate readings in . In this way, if you need to detect ordinary digital data signals, the measurement with the average value multimeter will not achieve the true measurement effect. At the same time, the frequency response of the AC signal is also quite necessary, and some can be as high as 100KHz.
Development Trend of Digital Multimeter
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 advent of dedicated chips for single-chip digital multimeters, a fully functional automatic range digital multimeter can be formed using a single IC, which creates 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 power consumption of the whole machine is very low.
