Apparatus for monitoring null card state of multiple towers

The utility model relates to a multi-tower empty section state monitoring device which is a device used for on-line detection that whether sections exist. Under the control of synchronous signals provided by a switch that is close to the external, a photoelectric switch is used for detecting whether a section is put on a printing device tower. The utility model can widely satisfy the on-line detection demand of printed device tower empty sections, such as folding machines, assembling machines, bookbinding machines, etc. The system comprises an optical isolating circuit, a communication circuit, an MCU circuit and a CPLD logic circuit. The utility model that adopts a connection of a serial port communication and a PLC upper computer can receive a configuration from the PLC; the multi-tower empty section state monitoring device is flexible in controlling method, can monitor the multi-tower empty section state on line and extend numbers of monitoring book towers according to field needs.