DC insulation monitoring instrument

A DC insulation monitoring instrument comprises a main controller and a subordinate controller, and is formed by a watchdog display keyboard circuit 1 which is connected with a serial communication circuit 2 and a voltage and leakage current sampling circuit 3 respectively, wherein the voltage and leakage current sampling circuit 3 adopts a single chip U1 to sample the bus voltage through a DC sensor H3, and collects the branch leakage current signals through multi-way switches U5-1 to U5-6 and an A/D conversion chip U4, the single chip U1 is adopted to upload the signals to the single chip U7 of the main controller through serial communication chips U3 and U11, the insulation state of the bus based on the data is judged, an order to the single chip U1 is given, and the data is transmitted to the remote through the serial communication chip U3 and a plug connector J15. The DC insulation monitoring instrument has the advantages that the fluctuation of the earth potential caused by the bus is avoided, the malfu