Patent GB-970158-A (GB)
Title: Traffic speed deviation computer
IPC: G06G7/76
Filed: 1960-10-13
Abstract: 970,158. Electric analogue calculating; indicating road occupancy. LABORATORY FOR ELECTRONICS Inc. Oct. 13, 1960 [Nov. 9, 1959], No.35173/60. Heading G4G. A traffic speed deviation computer comprises electric means continuously sensing the individual speeds of vehicles successively passing a point along a road, electric analog computing means providing a first output representing the square of the RMS of the speeds of a predetermined number of vehicles which have most recently passed such point and sensed by the sensing means irrespectively of the variation in time spacing between successive individual speeds; electric analog computing means providing a second electrical output representing the square of the arithmetic average of the speeds of such most recently passed predetermined number of vehicles sensed by the sensing means irrespectively of the variation in time spacing between successive individual speeds; and electric analog computing means receiving the first and second outputs and continuously deriving therefrom an output representing the difference therebetween; the square root of which represents the traffic speed deviation. It is shown that the traffic vehicle speed deviation is given by # = ##RMS<SP>2</SP>-#AA<SP>2</SP> where R#MS = the root mean square of the speeds of a predetermined number of vehicles #AA= arithmetic average speed of the predetermined number of vehicles. As shown in Specification 929,631, a radar sensing unit responsive to the passage of vehicles supplies a composite signal indicating passage of a vehicle and its speed to a Speed and Volume impulse translator also shown in Specification 929,631, which closes a detection contact and supplies a D.C. signal proportional to the speed with a detection pulse to a speed averaging unit 12, (Fig. 1) the detection pulse being time delayed at 5 to indicate vehicle passage through a roadway position such that the line passing the sensing unit to the position makes 60 degrees angle to the vertical; such pulse operating gate 17 to cut off the speed signal from calibration unit 18 which adjusts the amplitude and speed scale of the signal to energize capacitative electrical storage device 19. A mechanical storage device 20 incorporating an A.C. energized chopper and phase responsive reversible biphase servomotor controls a potentiometer developing a feedback voltage balancing the electrically stored voltage and driving cascaded squaring potentiometers 21 developing a squared output signal. On closure of gate 17 after time delay at 15, the signal electrically stored at 19 and the corresponding balancing signal mechanically stored at 20 represent the last vehicle speed LC while the output of squaring circuit 21 represents #LC<SP>2</SP>. The latter is applied to a "number of vehicles averaged" circuit 22 incorporating a variable voltage divider adjustable to a predetermined number, together with a signal from mechanical storage circuit 29 representing the squared RMS speeds of a preceding number of vehicles which is averaged with #LC<SP>2</SP> to give a new RMS<SP>2</SP> signal which is capacitatively stored at 23. At equality of the outputs of #LC electrical and mechanical storage circuits 19 and 20, null circuit 26 operates relay AIN to operate relay Ab in gate 24 to allow #RMS<SP>2</SP> mechanical storage circuit 29 comprising a chopper, amplifier and biphase servomotor operating potentiometer, to adjust to produce a signal equal to the signal stored at 23. At equality, null circuit 30 operates to open gate 24 and reset the apparatus for receipt of the next succeeding detector impulse and speed indication signal. Outputs representing #LC are derived on lead 35 and #RMS<SP>2</SP> on lead 36, which are supplied to deviation unit 13. The former is applied to "number of vehicles averaged" circuit 40 having a variable voltage divider adjustable to a predetermined number with and in similar manner to circuit 22; together with a signal from "arithmetical average speed mechanical storage" 46 incorporating a chopper, servoamplifier and servomotor during a potentiometer so that the output of 40 represents the average of the last vehicle speed signal and the average speed signal from 46 and applied through "not" gate 43 incorporating relay contacts to store a new arithmetical average speed signal in capacitative electrical storage circuit 44 whose output is connectible over gate 45 incorporating other relay contacts, to arithmetic average speed mechanical storage circuit 46, incorporating a chopper, servoamplifier and servomotor driving a potentiometer. Gates 43, 45 are operated inversely in response to relay AIN, directly and through a further relay so that prior to its operation the LC signal stored at 44 is adjustable through gate 43 in advance of the occurrence of null between storage circuits 19, 20. At null of the latter, relay AIN operates, allowing circuit 46 to be adjusted to the new value stored in circuit 44, while adjustment from circuit 40 is arrested; at the same time as circuit 29 is driven for adjustment to the new value stored on block 23. The squaring potentiometers in "arithmetic average speed squared" [#AA<SP>2</SP>] circuit 47 are driven from circuit 46, to produce an output signal representing #AA<SP>2</SP> fed to resistance capacitative difference computer 48 whose output representing #<SP>2</SP> is applied to a chopper-servoamplifier-servomotor, potentiometer 6<SP>2</SP> mechanical storage circuit developing a signal which energized a potentiometric squareroot circuit driven from 49 to develop at lead 50a a signal representing deviation 6 which may be displayed on a meter. The signal representing #AA<SP>2</SP> from 46 may also be metered. Indicator lamps may show operation of any servo system, and the deviation signal may operate a level sensitive relay. Fig.2 shows a modified speed averaging circuit in which the composite passage and speed signal from the radar sensing unit 10 energizes the speed and volume impulse translator 11 as a vehicle passes the radar to close contacts A and generates a D.C. speed signal on line 88 energizing angular position compensating potentiometer 60. The compensated signal is applied over diode 62 and contact T, to last car speed electrical storage capacitor 64. Closure of contact A on passage of a vehicle operates relay R through normally closed contacts S of relay S, and closes contacts R 1 , R 2 , R 4  to hold over A and R 1 . Opening of R 3  and closure of R 2  disconnects the charging circuit of capacitor CT and discharges it over variable resistor S 1 , allowing relay T to operate after a time delay. Closure of R 4  operates relay S to close and hold over normally closed contact V4 of relay V and S2 while closure of S3 energizes delayed operation of relay V; before which relay T operates to open T 2  and break the circuit energizing V. Contact T 1  closes to allow capacitor 61 to charge from potentiometer 60. At termination of the passage impulse, relay 170 is released and contact A opens to release relay R and open contacts R 1 , R 2 ,R 4 while closing R 3 . Relay R cannot now operate while relay S remains operative by reason of open contact S1 so as to prevent false operation by successive reflections from a long vehicle or a closely spaced second vehicle; prior to operation of the averaging unit by the first impulse. Relay R remains energized for the period of closure of contact A; inversely proportional to the speed of the detected vehicle so that the time of discharge and recharge of capacitor CT and the time delay between de-energization and release of relay T are determined inversely by vehicle speed. Release of relay R closes R 3  and charges CT over resistor 52 while it also is charging over relay T. At sufficient charge on CT, relay T releases to open contact T 1  and close contact T 2 . Relay V operates after a delay to open V 1 , V 4  and close V 2 ,V 3 to hold over contact V 3  and discharge capacitor CW over contacts V 2  and resistor 53. The capacitor was initially charged over variable resistor 53 and contact V 1  and over relay W. After a critical discharge time relay W operates to open W 1  and close W 2  thus connecting A.C, energized chopper 68 energized by the voltage on capacitor 64 held by opening of T 1  through cathode follower 66 to phase sensitive servoamplifier 90 and motor 91 which drives cascaded potentiometers 72, 74 generating on slider 73 and lead 35 a signal representing the square of the last vehicle speed and on slider 71 one representing last vehicle speed fed back to chopper 68, so that for null the servo drives to a position representing the last vehicle speed signal stored on capacitance 64. The squared speed signal is applied over resistance 75 to point 76 together with a signal from potentiometer 80 cascaded and driven to the potentiometer 82, to represent the square of the root mean square speed of a last predetermined number of vehicles; excluding the last vehicle whose speed is being measured. The combined voltage represents the square of the root mean square speed of the last predetermined number of vehicles including that whose speed is being measured. Energization of relay W opens contact W4 and closes contact W3 to controlledly discharge capacitor CX charged over W4 and variable resistor 56 and also over relay X. After a delay sufficient to allow adjustment of potentiometers 72, 74 by servomotor 91, and adjustment of charge on capacitor 85, relay X operates to open contacts X 1  and X 3  and close X 2 . Relay V is de-energized, opening V 2 ,V 3 and closing V 1 ,V 4 . Capacitor CW charges to de-energize relay W after a time delay allowing potentiometers 72, 74 to be re-adjusted, and contacts W 2 ,W 3  open and W1,W4 close. Capacitor CX charges to de-energize relay X after a time delay. Energization of relay X closes contact X 2  to apply the signal on capacitor