We first recall the expression of the effective value of the AC voltage, which is defined as follows:
We transform equation (1), square square, and order< P> Another expression of the true value voltage is obtained
from the (3), "taking the absolute value → square / division → taking average value" in turn, also The effective value of the AC voltage can be obtained, and this formula is more useful. For example: If a voltage variation range is 0.1V-10V, the square of U = 10mv-100V is required, which requires a considerable dynamic range (10000: 1), such a square circuit error may exceed 1mV. To output 100 V voltage, it is difficult to implement. If you use the formula (3), it is easy to design the circuit, and the accuracy can also be guaranteed. Therefore, most integrated monolithic validity / DC converters are designed with the principle of equation (3).
The core device of the true value instrument is a TRMS / DC converter. There are many integrated chips in the market, and this type of integrated circuit is generally used in the real value instrument. The single-chip integrated circuit has a high integration, perfect function, less peripheral components, simple circuit connection, and easy to guarantee energy indicators, such chips can accurately measure the effective value of various voltage waveforms in real time, and do not need to consider waveform parameters and Distortion, these properties are theof the average meter.