Method and apparatus for an active standby control system on a network

A hot standby system for a control system, comprising:

• a first and a second programmable logic controller, each programmable logic controller including:
• a network module board having a network address identifier, wherein the network address identifier is a Media Access Control address;
• a control unit having an operating state;
• an I/O scanner having a connection to a remote I/O head;
• and
• a hot standby module, the hot standby module of each programmable logic controller being operably connected together;
• means for assigning the address identifier to each network module board;
• means for operably connecting each network module board to a network;
• means for sensing the operating state of each control unit, and exchanging the network address identifier of the first programmable logic controller and the network address identifier of the second programmable logic controller upon detection of a failure in the first programmable logic controller;
• and
• means for resetting the connection between the I/O scanner and the I/O head in the first programmable logic controller prior to exchanging the network address identifiers.

A method of providing an active standby control system comprising the steps of:

• providing a first and a second programmable logic controller, each controller having an operating state and an I/O scanner having a connection to a remote I/O head;
• operably connecting the first and second programmable logic controllers to each other and to a network;
• assigning a network address identifier to designate each programmable logic controller wherein the network address identifier is a Media Access Control address;
• placing the first programmable logic controller in primary mode and the second programmable logic controller in secondary mode;
• sensing the operating state of the primary mode programmable logic controller;
• swapping the network address identifiers between the first and second programmable logic controllers upon detection of a failure in the first programmable logic controller, and placing the second programmable logic controller in primary mode;
• resetting the connection between the I/O scanner and the remote I/O head in the first primary programmable logic controller prior to swapping the network address identifiers;
• and
• transmitting reverse address resolution protocol (RARP) messaging to the network, wherein the newly designated programmable logic controller resume network operations.

An active standby system for a control system, the active standby system comprising:

• a first and a second programmable logic controller, each programmable logic controller having a network module board, each network module board having a separate network address identifier, wherein the network address identifier is a Media Access Control address, each network module board is operably connected to a network, each programmable logic controller comprising:
• a control unit having an operating state;
• a remote I/O head;
• a hot standby module, the hot standby module of each programmable logic controller is operably connected to each other and to the network, and is configured wherein the network address identifier of each network module board is exchanged upon detection of a failure in the first programmable logic controller;
• and
• and I/O scanner having a connection to the remote I/O head, wherein the first programmable logic controller is configured to reset the connection prior to an exchange of the network address identifiers.