The measurement methods of a multimeter and its alternating current frequency response
A digital multimeter can not only measure direct current voltage (DCV), alternating current voltage (ACV), direct current current (DCA), alternating current current (ACA), resistance (Ω), forward voltage drop of diodes (VF), current amplification factor of transistor emitters (hrg), but also measure capacitance (C), conductance (ns), temperature (T), frequency (f). It also adds a buzzer range (BZ) for checking the continuity of the circuit and a low-power resistance measurement range (L0Ω). Some meters also have an inductance range, a signal range, an automatic AC/DC conversion function, and an automatic capacitance range conversion function.
Generally speaking, the measurement methods of a multimeter mainly refer to the measurement of AC signals. As we all know, there are many types and various complex situations of AC signals. And with the change of the frequency of AC signals, various frequency responses occur, which affect the measurement of the multimeter. There are generally two methods for a multimeter to measure AC signals: average value measurement and true root mean square (RMS) value measurement. Average value measurement is generally for pure sine waves. It measures AC signals by estimating the average value, and there will be relatively large errors when measuring non-sine wave signals.
At the same time, if there is harmonic interference in the sine wave signal, the measurement error will also change greatly. True RMS value measurement calculates the current and voltage by multiplying the instantaneous peak value of the waveform by 0.707, ensuring accurate readings in distorted and noisy systems. In this way, if you need to detect ordinary digital data signals, using an average value multimeter for measurement will not achieve the real measurement effect. Also, the frequency response of AC signals is extremely important, and the frequency response of some multimeters can be as high as 100KHz.
The Development Trends of Digital Multimeters
Integration: Handheld digital multimeters use a single-chip A/D converter, and the peripheral circuit is relatively simple, only requiring a small number of auxiliary chips and components. With the continuous emergence of special chips for single-chip digital multimeters, using one IC can form a relatively complete automatic range digital multimeter, creating favorable conditions for simplifying the design and reducing costs.
Low Power Consumption: New-type digital multimeters generally use CMOS large-scale integrated circuit A/D converters, and the power consumption of the whole machine is very low.
