GB1017079A - Traffic control system and apparatus - Google Patents

Abstract

1,017,079. Road traffic signals. LABORATORY FOR ELECTRONICS Inc. Aug. 17, 1962 [Aug. 18, 1961], No. 31743/62. Heading G4Q. In a vehicle operated traffic control system an extendible green period is timed by a capacitor charging linearly as shown at 227, Fig. 6, and connected in series with an increasing bias voltage shown at 225, and the total voltage, shown at 228, is applied to trigger circuits which terminate the green period. In response to vehicle demands such as those shown at A1 and A2, the capacitor is discharged, but due to the increasing bias voltage the extensions granted are steadily reduced. When the total voltage is equal to the trigger voltage (shown as 160 volts) a first trigger fires and discharges the bias voltage (line 225) and allows the capacitor to continue charging along line 227-2 to time a passage time, at the end of which a second trigger fires and changes the traffic lights. Timing circuits.-The operation of the system is controlled by a line switch (Fig. 1, not shown) and in all positions, except the extendible green positions, D.C. is supplied to terminal 30, Fig. 3, to add a steady bias to the potential of the timing capacitor 121. The capacitor is connected to a cathode follower 125 the output of which is coupled to the charging circuit through two neon tubes 126 and 127 to provide a constant charging voltage and ensure linearity. The contacts LR-4 are normally closed and the output at 134 is connected to a trigger circuit F.3b which operates a relay AS which energizes a motor magnet to step on the line switch. In the extendible green positions relay LR is energized to change over contacts LR-4, and a bias circuit, Fig. 2 (not shown), is connected to terminal 30. A maximum time circuit, Fig. 4 (not shown), is also connected in circuit to limit the extendible period. In the absence of demand for change of right-of-way a relay VR (not shown) operates and prevents the bias and maximum time circuits from starting, and its contacts VR-3 short-circuit the input to F.3a to prevent this unit from working, so the green period continues until there is a demand for a change. When there is such a demand the bias at terminal 30 starts increasing in accordance with the charging of a capacitor in the bias circuit, Fig. 2 (not shown), and each time a vehicle is detected in the road having right of way'capacitor 121 is discharged through the vehicle operated contact AD-5 or BD-5. When the total voltage at point 134 is sufficient the trigger circuit F.3a fires and energizes relay PR which discharges the bias voltage and deenergizes relay LR, thereby switching the output at 134 to F.3b. When capacitor 121 charges sufficiently F.3b fires and energizes relay AS to step the line switch on to its next position; during this charging period contact LR-5 is open so that capacitor 121 cannot be discharged by operation of the vehicle contacts AD-5 and BD-5.