52 54 56 and 58 as shown if the number of work stations is less than five the switch and relay assemblies directly bypass or pass through the ibm analog loop signal a detailed schematic diagram of the switch and relay assemblies 50 52 54 56 and 58 is given in fig7 wherein a representative assembly 34 n 34 is depicted the assembly 50 consists of a 3 pole double throw switch 60 and a double pole relay 62 beginning with the operation of the 3pdt switch 60 if the switch is in the out position signals from assembly number n 1 are fed directly to assembly number n and the output to and input from work station n are not used this is the situation when no work station is to be connected to assembly n if the switch is in the output from assembly n 1 is supplied to work station n and the output from work station n is supplied to assembly n 1 this is the normal mode in which work stations are attached to the lla the third pole of the switch controls a voltage to the controller subsystem if the voltage equals v the switch is out and no work stations are connected to assembly n if the voltage equals 0 a work station is connected to assembly n the information as to whether or not a work station or terminal is connected to a particular assembly is used by the controller in determining the existence of fault conditions the diagnostic messages are set forth in fig9 a two pole double.