| 摘要 |
A method and apparatus for determining whether cargo is present in a freight car. The freight car has a proximal ("rear") end with a loading door and opposing, distal ("front") end. One or more transmitters and receivers are mounted inside the freight car at the front end, toward the car's ceiling. The transmitters/receivers are operated by a controller, which also functions to analyze data from the transmitters/receivers and transmit related reports to a remote monitoring site. During a prescribed time period, a transmitter generates an ultrasonic signal pattern with a coverage area of prescribed radius that terminates before reaching the loading door. During the time period of transmission, or slightly later to account for signal reflection time, the controller operates the receiver to detect reflected signals originating from the transmitter. Then, the controller transmits a report of whether cargo is present in the freight car, based on whether any reflected signals were received.
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