Importance

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Abstract

The speed proportional frequency signal from the speed generator being checked is amplified and applied to a highpass filter-rectifier with a low frequency limit corresponding to a predetermined minimum train speed. Polarity of the rectified output is opposite to the DC operating energy so that, with four-terminal load resistor and smoothing capacitor, the filter-rectifier operation is vital. The rectified signal activates an oscillator level detector when its level exceeds the breakdown of a Zener diode control device selected to correspond to minimum speed output. The level detector is coupled by a stepdown transformer to a differential amplifier biased by a signal supplied from an associated zero speed detector. The bias signal has sufficient level to enable the differential amplifier to produce an output in response to the level detector input only when the train speed is greater than zero. This output represents proper operation of the axle generator and is coupled to enable the train speed governor to respond to other train control signals. When the train is stopped, the differential amplifier is biased below operating level. However, a supplemental bypass signal present only when train brakes are set is coupled through the differential amplifier output to enable the speed governor during station stops.

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First Claim