Primary-secondary monitoring circuit applied to metro engineering vehicles

The invention discloses a primary-secondary monitoring circuit applied to metro engineering vehicles. The positive pole of a control power supply is connected with the negative pole through a first relay normally-opened contact, a diode and a time replay. The positive pole of the control power supply is connected with the negative pole through a primary and secondary selective switch assembly and a secondary replay coil, the first relay normally-opened contact is in parallel connection with the normally-closed contact of the time relay, and the other end of the primary and secondary selective switch assembly is connected with a first relay coil. A first reconnection cable is connected with the diode of each engineering vehicle, after a second replay normally-opened contact is in series connection with a first relay normally-closed contact, one end is connected with the first reconnection cable, and the other end is connection with a second reconnection cable. One end of a third relay coil is connected with the second reconnection cable, and the other end of the third relay coil is connected with the negative pole of the control power supply. The diode is combined with a relay, the state that whether the second reconnection cable is connected with the power supply is monitored, and whether the fault situation that a plurality of operation ends are selected to be the main operation ends exits is determined.