The voltage detection is relatively simple, and the voltage sensor is connected to the line end of the voltage to be measured.  
The current detection also depends on voltage detection, and then calculates the current. There are two ways in total:  
1. Mutual detection method. Mutual detection method is generally used in high -voltage and large current situations (communication). In the interoperability circuit, when the main winding flows are too different, the side winding feels the corresponding height and different voltage. Read out the voltage value of the interoperability, and you can calculate the current flowing through the main winding.  
2. Resistance detection method. The resistance detection method is generally used for low -voltage small current occasions. When the current flows through the resistor, the corresponding voltage will generate at the end of the resistance. Read the value of this voltage to calculate the current flowing through the resistance.