Chapter II Fundamental Principles
The fundamental principles are as shown in Fig.1:
Equipment to be measured
Current sensor
Amplified
Sampling hold
A/D
Keyboard
Bus
Single chip microcomputer
Measured power supply input
Voltage sensor
Display device
Fig. 1 Diagram of Fundamental Principles
As shown in Fig.1, the instrument is composed of the analog part and the digital part. The analog
part is mainly composed of circuits i.e. sensor, program-controlled amplifier, sampling holder and
A/D. the digital part is composed of microcomputer, data accumulator and display device.
After passing the voltage sensor, the measured voltage signal will be decreased to the weak
voltage. According to the signal size, it will be controlled by the microcomputer for range
programmable gain; through the sampling holder, the voltage can be transformed into the digital
signal by the analog/digital transformer A/D; the digital signal will be transmitted into the
microcomputer to calculate the true-value of voltage (URMS) and output the value to the display
device.
After passing the current sensor, the measured current signal will be decreased to the weak current
signal, just like the measured voltage, after the process of programmable gain, sampling hold and
A/D transformation, the true-value of current (IRMS) and current peak (Ip) will be calculated and
displayed in the microcomputer.
The true-value of voltage (U
RMS
), true-value of current (I
RMS
), active power (P) and power factor
(PF) peak shall be measured according to the following formulas:
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