Apparatus and method for supervision

A communication system comprising:

• at least first and second communications links;
• a plurality of branches coupled between the links wherein each of the branches includes a plurality of communications units coupled thereto and circuitry for selectively blocking the communications between the links on all branches except for one;
• circuitry for sending a communication signal on the first link and detecting the communication signal on the second link;
• circuitry for generating a trouble condition if the communication signal is not detected on the second link;
• and
• wherein the trouble condition is an open circuit in the branch and the location of the open circuit is determined by a common controller sending a command for the devices from both the first link and the second link and the devices that do not receive the command from both links send an open circuit message to the common controller.

A communication system comprising:

• at least first and at least second communications links;
• a plurality of branches coupled between the links wherein each of the branches includes a communications unit in each branch which unit includes circuitry for blocking the communications between the links;
• circuitry for sending a communication signal on the first link and detecting the communication signal at the respective communication unit of each branch;
• additional circuitry for sending a communication signal on the at least second link to the communication units and indicating a selected condition if the respective communication units did not receive both the communication from the first link and the at least second link;
• and
• where there is an open circuit in the branch, the location of the open circuit is determined by a common controller sending a command for the devices from both the first link and the second link and the devices that do not receive the command from both links send an open circuit message to the common controller.

A communication system comprising:

• a first and at least a second communications link;
• a plurality of branches coupled between the links wherein each of the branches includes a communications unit within each branch which is capable of blocking branch communications between the links,
• circuitry for sending a communication signal on the first link and detecting the communication signal at the respective communication unit within each branch;
• further circuitry for sending a communication signal on the at least second link to the communication units within the branches;
• and indicating an open circuit trouble condition if the communication units within the branches did not receive both the communication from the first link and the at least second link;
• and
• wherein the location of the open circuit is determined by a common controller sending a command for the devices from both the first link and the second link and the devices that do not receive the command from both links send an open circuit message to the common controller.