Patent GB-975532-A (GB)
Title: Apparatus for traffic supervision
IPC: G08G1/054
Filed: 1962-03-05
Abstract: 975,532. Measuring short time intervals. AGFA A.G. March 5, 1962 [March 8, 1961], No. 8487/62. Heading G1U. [Also in Divisions G4 and H3] A traffic supervision device for indicating whether a vehicle is exceeding a fixed maximum speed comprises two detectors, a time switch actuated by the passage of a vehicle over the first detector and having a running down period corresponding to the maximum speed, and an indicator or recording device (e.g. a camera) operated on actuation of the second detector provided the latter is actuated during said running down period, and is characterised by the provision of means for preventing the re-operation of the device for an "interruption" period after expiry of the "running down" period without the indicator having been operated. Circuit (Fig. 2) Circuit 6 includes switch 13, 14 operated together by the first road pad detector, and relays 18, 19 and thyratrons 16, 17 which control the "interruption" period. A time switch comprising the thyratron 17 and associated R.C. elements 25, 26 is set to a time corresponding to a minimum speed for travelling between the two road-pad detectors. A further time switch in a circuit 7 comprises a thyratron 36 capacitor 37 and a resistor 38 and is set for a time corresponding to the maximum permissible speed. The camera is operated by a circuit 8. Operation:A vehicle travelling below the maximum speed but above the minimum speed in passing over the first detector closes switches 13, 14 to energize a delayed action relay 15 which locks over contacts 42a, 15a. The bridging of capacitor 37 of the "minimum speed" timer is removed by opening of contact 15c and the timer 36, 37, 38 begins to "run". On striking of valve 36, after expiry of the "maximum speed" time period, a relay 42 is energized whereupon relay 15 is deenergized, and since the vehicle has not reached the second detector operating road-pad switch 33 before contact 15b opens again, subsequent closing of switch 33 as the vehicle passes over the second detector will have no effect on the camera circuit. Before valve 36 has been extinguished (at contact 15d) valves 16,17 are struck (over contact 42a) one after the other thereby energizing respective relays 18, 19. The "interruption" period is determined by time switch 17, 25, 26 and the discharge time of capacitor 29 after which period the whole apparatus returns to its original condition. During the interruption period, the energization of relay 15 is prevented by relay 19 even though a car may operate the first detector, and the system cannot therefore give an erroneous indication, due to the presence of a second vehicle, that the first vehicle is travelling too fast. Operating when vehicle exceeds speed limit The vehicle will reach the second detector before the expiry of the "run down" period of time switch 36, 37, 38 and therefore closes switch 33 before valve 36 strikes. Relay 34 is energized thus energizing relay 35 via 34a (releasing relay 34 at 35b) and the camera operating relay 43 receives a short current pulse. A switch 34b is closed for a short time (owing to the delayed release of relay 34), the capacitor 37 is discharged and on opening of switch 34b its charging begins again and a new timing period is initiated. After a period determined by resistor 39, which is switched in instead of resistor 38 by the changeover of contact 35c, valve 36 strikes and the camera relay 43 is again energized to take a second photograph. The interruption device 16, 17, 18, 19 is prevented from operating in this case by relay 35 and the whole system then reverts to normal. An optical or acoustic indicator may be used instead of a recorder. Specification 910,526 is referred to.