Fault isolation and recovery in a distributed control network

In a control network comprising a plurality of nodes connected in a loop and communicating over a continuous bidirectional common bus, at least one of said nodes being designated as a master node and one or more of said nodes being slave nodes, a method comprising the steps of:

• (a) detecting a fault condition;
• (b) isolating each node from its adjacent nodes except for an impedance between each node and its adjacent nodes by breaking said common bus into a plurality of bus segments, such that a separate bus segment connects each pair of adjacent nodes;
• (c) transmitting over said common bus a de-isolate control message from the master node to the nearest isolated slave node with respect to the master node;
• (d) receiving the de-isolate control message at said nearest isolated slave node unless the fault condition prevents receipt of the de-isolate control message;
• (e) de-isolating said nearest isolated slave node in response to receiving said de-isolate control message at said nearest isolated slave node, thereby causing the nearest isolated slave node to become de-isolated;
• (f) sending over said common bus a de-isolation acknowledgment message from said de-isolated slave node to said master node;
• and
• (g) repeating steps (c) through (f) until a nearest isolated slave node fails to receive the de-isolate control message due to the fault condition.

A control network comprising:

• a common bus for bi-directional communication;
• a plurality of nodes communicatively connected to said common bus, said nodes comprising
• a master node, and
• a plurality of slave nodes connected to said master node in series connection such that each node is connected to two adjacent nodes and each pair of adjacent nodes is connected across one of a plurality of bus segments of said common bus, said nodes collectively forming a loop;
• a plurality of fault detection circuits, at least one fault detection circuit at each node;
• and
• a plurality of isolation circuits, at least one isolation circuit located at each node, each isolation circuit allowing signals to pass unimpeded across said common bus when in a non-fault mode impeding signals across said common bus by impeding signals between two adjacent bus segments connected to said node upon detection of a fault by said fault detection circuit, and resuming unimpeded passage of signals across said common bus after receiving a de-isolation instruction from the master node over said common bus;
• wherein the master node transmits de-isolation instructions sequentially to each slave node over said common bus to determine the location of said fault.

In a control network comprising a plurality of nodes connected in a loop such that a portion of a continuous, bi-directional common bus connecting the nodes passes through each node, and wherein at least one of said nodes operates as a master node and one or more of said nodes operate as slave nodes, a method comprising the steps of:

• (a) detecting a fault individually at each node;
• (b) in response to said fault, increasing an impedance at each node of the portion of the bus passing through the node so that signals cannot freely propagate around the entirety of said loop;
• (c) transmitting a control message from the master node over said common bus to a slave node adjacent to the master node;
• (d) receiving the control message at said nearest slave node unless the fault condition prevents receipt of the control message;
• (e) decreasing the impedance at said nearest slave node in response to receiving said control message at said nearest slave node;
• (f) sending a response message from said nearest slave node over said common bus to said master node;
• and
• (g) repeating steps (c) through (f) for each slave node in series until a slave node fails to receive the control message due to the fault condition.

A control network, comprising:

• a plurality of nodes, said nodes comprising a master node and a plurality of slave nodes;
• and
• a bi-directional common bus, said nodes connected to said bi-directional common bus in a loop configuration;
• wherein each node comprises a shunt circuit and a transceiver connected to said shunt circuit through a first impedance element;
• wherein said shunt circuit comprises a controllable switch in parallel with a second impedance element, said shunt circuit at each node connecting together two adjacent segments of said bidirectional common bus;
• wherein each node maintains the switch at its respective shunt circuit closed when in a non-fault mode, thereby allowing free propagation of communication signals around said bidirectional common bus;
• wherein each node opens the switch at its respective shunt circuit in response to detection of a fault condition, thereby connecting each pair of adjacent segments of said bi-directional common bus together by said second impedance element of said node;
• and
• wherein, in response to said fault condition, the master node sequentially instructs the slave nodes to close the switch of each slave node's respective shunt circuit.