Patent GB-888386-A (GB)
Title: Arrangement for measuring speed by means of the doppler effect
IPC: G08G1/054
Filed: 1958-10-24
Abstract: 888,386. Doppler radar. TELEFUNKEN G.m.b.H. Oct. 24, 1958 [Oct. 25, 1957; June 25, 1958 (2); June 26, 1958 (2); June 28, 1958], No. 34117/58. Class 40(7). An arrangement utilizing the Doppler effect for determining the speed of road vehicles employs a tuned reed type of frequency meter to measure the Doppler frequency. The latter frequency, which is derived in conventional manner by heterodyning an oscillatory signal with the same signal after reflection by the vehicle, is supplied to the energizing coils of the tuned reed frequency meter each reed Z 1 -Z n  (Fig. 4a) of which is arranged to close a contact when its amplitude of vibration exceeds a predetermined level. On the closure of any one such contact, this being determined by the particular reed which responds to the received Doppler frequency and hence indicative of the speed of the vehicle, an associated relay N 1 . . N n  operates and, in addition to operating its associated holding contact n 11 . . n n1  operates an appropriate one of the contacts n 12 . . n n2  (Fig. 4b) in the circuits of indicator lamps L 1 ..L n  which when illuminated indicate the speed corresponding to the particular Doppler frequency. On the entry of a vehicle into the zone covered by the radiator of the oscillatory signal any speed indication due to a previous vehicle is cancelled by the opening of contact l (Fig. 4a) of a relay L (Fig. 4c) operated via contact a 1  of relay A (Fig. 4a) which is energized whenever a Doppler frequency is received. After a short interval determined by the network R.C. a relay V operates and its contact v breaks the circuit of relay L thus allowing I to close and the speed measuring arrangement to operate as described above. For economy reasons sufficient tuned reeds and associated relays and indicator lamps to cover speeds slightly in excess of a known speed limit only are provided. When, however, it is desired to provide an indication of speeds very much in excess of such limit a circuit arrangement is employed in which a H.P. filter passes only those Doppler frequencies which exceed a predetermined value to a rectifier circuit from which operating current for a relay controlling an excess speed indicator is derived (Fig. 5, not shown). In addition to providing speed indications the apparatus may be arranged also to provide information as to the lengths of the various vehicles in the measuring zone and hence give an indication of the type of vehicle, e.g. cycles, private motor cars, lorries, &c. Such additional apparatus is shown in Fig. 6 and comprises three condensers C<SP>1</SP> 1 , C<SP>1</SP> 2 , C<SP>1</SP> 3  each of which when fully charged conditions the next one to receive charge and which are arranged to be charged in the order G<SP>1</SP> 1 , C<SP>1</SP> 2 , C<SP>1</SP> 3  via appropriate ones of the resistors R<SP>11</SP> 1 . . R<SP>11</SP> 5 , depending on which of the switches n<SP>11</SP> 1 . .n<SP>11</SP> 5  is closed by the speed indicating relays N 1  . . N n  of Fig. 4a and via resistors R<SP>1</SP> 3  . . R<SP>1</SP> 5 , the former resistors being so selected that, having regard to the speed of the vehicle, an indication of its length in increasing size is given by the condition of the circuit, i.e. whether one, two or all three condensers are charged, when the vehicle has left the measuring zone. Other facilities which may be provided in addition to the speed measurement include, the recording and classification of vehicles according to length and speed of travel (Fig. 7, not shown), the determination of the particular one of two possible directions of travel of the vehicle under measurement (Figs. 9 and 10, not shown) and the control of pnotographic equipment for photographing vehicles which exceed a predetermined speed (Figs. 11, 12 and 13, not shown).