Three-phase asynchronous motor current sampling resistance

Sampling resistance and HCPL - 7840 connections, sampling resistor R1 is end connected to the Vin +, the negative terminals of fan cover the sampling resistor connected to the Vin? The real-time motor current is converted into analog voltage input chips; At the same time Vin? GND1 connection, and the return path of power supply and the sampling line connected to the negative terminals of the sampling resistance, because www.dongfeng-motor.com it is a lot of current when motor at work through the sampling circuit, parasitic inductance in the circuit can produce a large current spike, but this kind of connection can take these transient noise as a common mode signal, not for the sampling current signal interference; In addition, to eliminate the high frequency noise, sampling current input signal sampling resistor small diesel generator on the voltage signal have been collected by the R2 and C3 of low-pass filter into the chip.