An apparatus and method are disclosed which find particular utility as a component of a traffic control system known as a conflict monitor. The apparatus includes a number of solid state switches which are activated to scan inputs from traffic control signals. The inputs are sequentially applied to a A-D converter which samples the voltage and applies it to a microprocessor which is programmed to determine the voltage and analyze the signals for conflicts, or other errors. The input lines are also connected to terminals of a program board whereby the microprocessor can instruct a switch to ground the common pin on the program board to allow program board inputs to be applied to the microprocessor for indicating permissible conflicts. A method includes a technique for determining the voltage of an input analog signal by scanning a plurality of input signals and sampling them in accordance with a relationship which provides minimum error. A display may be operated in one of two modes. In the first mode, a display indicates the signals involved in a conflict, or other error determination. In a second mode, the display may be sequentially stepped through each signal to determine its particular state at the time of a conflict.
A method and apparatus for monitoring for Red Fail faults in a traffic signal control system. Traffic control signals generated by a traffic control unit are grouped into channels. Certain channels are specified for Red Fail testing in which all lights in a given channel are inactive at the same time. Channels which are not specified are not subject to Red Fail testing, but other conflict testing can still be performed on these unselected channels.
A method and apparatus for monitoring for Red Fail faults in a traffic signal control system. Traffic control signals generated by a traffic control unit are grouped into channels. A parent-child relationship is established between some channels. When testing for a Red Fail fault, the control signals in both the parent channel and the child channel are examined. A Red Fail fault will occur only if all the control signals examined in both the parent and the child channel are inactive. The control signals examined in the child channel can be limited to the Green and Walk signals; or may include the Yellow signals.
The control signals and associated output signals of traffic signal switching circuits are continuously monitored by a microprocessor. In the event of a microprocessor-detected failure of a switching circuit, a microprocessor controlled back-up switching circuit is available to maintain normal operation of the signal.
