Abstract: Hot-box signalling devices are disclosed for indicating the presence of overheated bearings in vehicles such as rail cars. The device includes means defining a closed compartment containing a fluid and pressure-sensitive means communicating with the compartment. The compartment is arranged in thermal communication with a bearing of the vehicle so that increases in the temperature of the bearing cause increases in the pressure exerted by the fluid. The pressure-sensitive means is adapted to produce a signal when the pressure exerted by the fluid exceeds a predetermined threshold representing an over-temperature condition in the bearing. Preferably, the pressure-sensitive means takes the form of a plug normally closing an opening in the compartment, and a marker material, the plug and marker material being expelled when the pressure in the compartment reaches said predetermined threshold. In one aspect of the invention, provision is made to compensate for ambient temperature.

Abstract: A warning indicator including a housing attachable to the wheel and axle assembly of a railway car. An ejector assembly in the housing is spring biased to deploy a visual indicator in the presence of abnormal bearing temperatures. A fusible retainer, upon being subjected to abnormal temperatures, releases a stem of the ejector assembly which carries a visible indicator, such as a streamer, outwardly into the airstream for display in a highly visible manner. The indicator housing is provided with tool receiving surfaces to facilitate indicator installation and removal.

Abstract: An improved circuit is provided for differentiating between roller bearings and friction bearings in a railroad hot box detector system. The improved circuit integrates the waveform generated by a bearing scanner and compares that to the integral of a pre-selected portion of the waveform. By this method of comparison, irregularities in the system due to noise are obviated.

Abstract: An apparatus for determining the temperature of railroad car wheel journals (i.e., "hotbox" detector) includes a sensor including a pyroelectric cell responsive to infrared radiation signals, which are focused onto the cell, to output voltage signals as a function of the radiation signals inputted thereto. The sensor exhibits a nonlinear gain response to different frequencies of input signals and compensation is provided by coupling the output of the sensor to a differentiating circuit which has a similar but relatively negative gain response. The output of the differentiating circuit is a substantial voltage replica of the infrared input signal and this voltage signal may be applied to a suitable utilization device such as one which records journal temperature and/or provides a suitable alarm when a sensed journal temperature exceeds a predetermined value.

Abstract: A normally inactive sound signal generator is supported from the rotatable axle of each railway car in a train and actuatable to generate a predetermined signal in response to a hot box condition. Electrically operable signal receivers coupled to electrically operable radio signal transmitters are spaced along the railroad track at predetermined intervals which may be 4,000 to 6,000 feet apart and the receivers and transmitters are operable on low magnitude current, such as provided in the rails of the track for Centralized Train Control Systems.