Patent GB-1174748-A (GB)
Title: Apparatus for Detecting Vehicles
IPC: G08G1/042
Filed: 1968-07-24
Abstract: 1,174,748. Road traffic detectors. TATEISI ELECTRONICS CO. 24 July, 1968 [17 Aug., 1967], No. 35354/68. Heading G4Q. In apparatus for detecting vehicles having a detector element 1 dimensioned to extend across a plurality of lanes, the output from the detector is changed by the presence of a first vehicle in the field of the detector and is compared with a first reference value to give an output S1 indicating the presence of the first vehicle, the output is also memorized in a circuit 12 and a signal corresponding to the difference between the memorized value and the output from the detector is also determined and this is compared with a second reference value to produce a second output S2 upon the detection of at least one more vehicle in addition to the first vehicle. As shown, when a vehicle M1 is in the field of the loop 1, the frequency of oscillator 2 is reduced. The output (A, Fig. 2, not shown), from mixer 4 obtained by comparing the output of oscillator 2 with a reference oscillator 3, increases and is fed to trigger a monostable circuit 5. The output (B) from the monostable circuit 5 is integrated at 6 and passed via an amplifier 7 to a Schmitt circuit 8 so that when the amplifier output (D) reaches a certain value (V1) the circuit 8 switches to indicate at S1 the detection of the vehicle M1 The output (C) of the integrating circuit is periodically reset. The change in output of the Schmitt circuit 8 resets flip-flop 10 so as to enable AND gate 11 to pass the output S1 so as to charge a capacitor C2 (I), and turn ON field effect transistor Tr2. Each output pulse from the monostable circuit 5 turns on transistor Tr1 so that output pulses (J), corresponding to the difference between the output of 5 and charge on capacitor C2, of decreasing amplitude are fed via C1 to an integrating circuit 13. The output (K) of the integrating circuit 13 is amplified at 14, and when the output (L) of amplifier 14 is less than a predetermined value (V2) the output of a Schmitt circuit 15 is such as to reset the flipflop 10 and prevent any further charge occurring on C2. If the vehicle now passes out of field of the loop 1 the output of the Schmitt circuit 8 changes to zero and discharges C2 to reset the arrangement. However, if the first vehicle M1 is still in the field of the loop and a further vehicle M2 occurs in the next lane to also effect the field of the loop 1, the output from the oscillator is further reduced, this increases the output frequency (A, Fig. 3, not shown), from mixer 4 and that (B) of the monostable circuit 5. The output from the circuit 5 is compared with the stored voltage on the capacitor C2 in circuit 12 and the output (C) from the integrating circuit now increases in value. When a certain value (V3) output from the amplifier 14 is reached, the output of Schmitt circuit 16 is changed. As Schmitt circuit 15 no longer holds the flip-flop 10 reset it becomes set by the output from 8 and gate 17 is enabled to give an output S2 indicating the presence of another vehicle M2 as well as M1. The detection of vehicles in three or more lanes may be achieved by connecting a corresponding number of further comparing circuits 16 and gates 17. Traffic control of cross-roads (Fig. 4).-A detector loop 1 may be arranged across a lane for left turning vehicles and a lane for straight ahead and/or right turning vehicles. Control of the traffic signals for these lanes is then obtained from the detector. Assuming a vehicle M4 is waiting to turn left this gives an S1 output from the detector arrangement. Vehicles passing over the detector to go straight ahead or right give outputs S2. When no output S2 occurs the traffic control signals can be changed to allow vehicles to turn left.