Abstract: The invention provides a 3-wire multiplexing system exhibiting high noise immunity, particularly suitable for industrial control applications. A master station provides AC power, and clocking and synchronization information, for a plurality of remote transmitter and receiver stations. A 3-wire cable links the master station and the remote stations. Two wires of the cable are power lines L1 and L2 and are isolated from each station by respective transformers. The third wire is a data line and is optically coupled to the remote stations. The remote stations are thus completely isolated from the cable, yet powered, clocked and synchronized therefrom without the need for local power supplies or local clocks. The signaling method switches the data line onto the power lines, and provides a high degree of data security by recognizing both the polarity and the position of a pulse on the data line within an AC cycle.

Abstract: A line of 2-wire pilot devices using current level as a signal for implementing solid state control systems. A variety of alternative pilot devices such as flag type limit switch, magnetic type proximity switch, capacitance type proximity switch and temperature responsive switch, in addition to pushbutton switch, are usable as logic inputs to the system based upon two intermediate current levels. Shorted lines and open lines are detected by zero voltage and zero current levels, respectively. A variety of alternative outputs such as logic output and relay output are also useable in the system. In addition, tachometer and motion transducer systems with pulse inputs and pulse integrator and non-volatile memory outputs, respectively, are further possible modifications of the system.

Abstract: A system for protecting an electrical resistor, such as, for example, the dynamic braking resistor of a D.C. traction motor used in a diesel-electric locomotive, from burn-out in the event of a malfunction such as a cooling fan failure or air blockage, over-load, high ambient temperature, etc. Such protection is afforded by a noise-immune system that continuously monitors the resistor temperature and provides an output signal when the resistor temperature reaches a predetermined level above its normal operating temperatures short of an unsafe level. This is done by sensing the change in resistivity of the resistor with change in temperature thereof to provide a first control signal. A second control signal proportional to the current in the resistor is obtained and compared with the first control signal to obtain the aforesaid output signal proportional to the resistor temperature above ambient temperature.