This product uses special isolation module to monitor the AC voltage in the power grid and circuit in real time. When the AC voltage exceeds the set upper limit, it outputs the alarm signal of exceeding the limit, and the output signal is the relay contact signal. Within the range of the input range, the action limit value of the AC voltage can be set arbitrarily. The product is completely isolated from input and output, and has the characteristics of high precision, high isolation and low source displacement. It can be applied to motor overload monitoring, power loss detection, action verification, signal isolation and conversion.