| 摘要 |
Primary and secondary vehicle sensors are utilized to detect vehicles moving along a roadway, this information being available for use in a traffic control system. Primary and secondary counters associated with the primary and secondary vehicle sensors respectively are driven by a timing pulse source. The counters are reset to zero in response to their associated vehicle sensors so that the maximum count thereon is indicative of the time between successive actuations of such sensors. A timing limit selector is utilized to select a timing interval indicative of a probable failure in the operation of either of the vehicle sensors. This selected timing output is separately compared with the outputs of the counters, and when coincidence between the selected timing output and the output of either of the counters is reached, a failure signal is generated. This failure signal is utilized both to actuate an appropriate fail indicator and to control logical gating circuitry to provide an output signal solely in response to the vehicle sensor not associated with this failure signal.
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