Patent GB-1003823-A (GB)
Title: Traffic actuated control apparatus
IPC: G08G1/081
Filed: 1961-09-12
Abstract: 1,003,823. Road signals for controlling traffic. LABORATORY FOR ELECTRONICS Inc. Sept. 12, 1961 [Sept. 12, 1960], No. 32710/61. Heading G4Q. A master controller for traffic signals comprises means for measuring traffic flows in two different directions, e.g. inbound and outbound, and means for producing different outputs according to whether both flows are below a minimum value, at least one flow is above a minimum value, or one flow is above a minimum value and exceeds the other flow by a predetermined amount. Measuring and comparing traffic flows.-A vehicle detector 33, Fig. 3, operates a relay 64, of which one contact 80 lights a lamp 81 and another contact 83 causes a capacitor 85 to charge through a triode 90. When the relay is released, capacitor 85 discharges into a capacitor 95 provided with a discharge circuit including a potentiometer 99 which may be adjusted to set a desired volume of traffic as equal to 100%. The voltage at junction 104 is proportional to the charge on capacitor 95 and therefore to traffic flow, and this voltage is averaged by a capacitor 110 in conjunction with a resistance selected by switch 109 to set the averaging period. The voltage on capacitor 110 is applied to a cascaded cathode follower formed by triodes 112 and 113 to produce an output at junction 120 which can be displayed on a meter 121. The output from junction 120 is fed to a terminal 125 which may be connected to an external recorder, and is also fed through a potential divider to the grid of triode 140. Two potential dividers, one of which is selected according to the condition of relay 65, each include an adjustable potentiometer 132 or 135 to adjust the levels at which triode 140 conducts or cuts off and energizes or releases the relay 65. The junction 120 is also fed through one of a similar pair of potential dividers to the grid of triode 71. A second similar traffic measuring circuit is adapted to operate a relay 65<SP>1</SP> and to produce an output on line 69<SP>1</SP> which is fed to the grid of triode 70. Triodes 70 and 71 form a difference circuit which operates relay 66 when one traffic flow exceeds the other. A similar relay 66<SP>1</SP> is operated when the other flow exceeds the first. The circuit shown measures and compares traffic volumes, i.e. vehicles per unit time, but may be modified to measure traffic density, i.e. vehicles per unit distance, or may compare average speeds of traffic flow. Relay circuits in the master controller.-Fig. 3a shows a circuit for providing an output signal in accordance with the conditions of relays 65, 65<SP>1</SP>, 66 and 66<SP>1</SP> of Fig. 3, and includes three synchrolizers 173-175, each comprising a constant speed motor rotating a set of cams adapted to open and close contacts, for example once every 60 seconds. With the four relays de-energized and all contacts in the positions shown, synchrolizer 173 is energized and its contacts 3E and 3F make to energize relay 169 and so supply power to an output lead 166. Contacts 3C and 3D open to open a lock relay 163 and thereby prevent the four relays 65 and 66 from influencing the output until the end of a cycle. If one of the two relays 65 is energized, or if a manual switch 176 is closed, relays 170 and 180 and an indicator lamp 192 are energized, and synchrolizer 173 is again energized. Relay 180 causes power to be supplied to two output leads 164 and 165. If relay 66 is energized, relays 172 and 182 and an indicator lamp 203 are energized, and so is synchrolizer 175; the latter operates relay 169, so that power is supplied to lines 166 and 165. If relay 66<SP>1</SP> is ener - gized, relays 171 and 181 and synchrolizer 174 are energized, and power is supplied to lines 166 and 164. Lines 164-166 pass to local controllers where lines 164 and 165 may operate a pair of relays to select one of four timing units controlling traffic signals, Fig. 2 (not shown); line 166 carries the synchronization signal. Specifications 674,590, 824,651 and 985,214 are referred to.