Patent GB-391416-A (GB)
Title: Electric tachymeter
IPC: G01P3/68
Filed: 1931-07-13
Abstract: 391,416. Current-duration meters. SOC. C. E. M. A. CONSTRUCTIONS ELECTBO-MECANIQUES D'ASNIERES, 236, Avenue d'Argenteuil, AsniÞres, Seine, France. July 13, 1931, No. 20135. Convention date, July 12, 1930. Void. [Published under Sect. 91 of the Acts]. [Class 37.] Comprises apparatus for measuring the time interval between two phenomena for measuring speed of vehicles, echo sounding, &c. by causing occultations of two beams of light (including ultra-violet or infra-red rays), condenser being charged during the period between the occultations, the voltage of the condenser being applied to the grid of a 3-electrode valve, the variation in the anodecurrent of which is a measure of the time interval between the occultations which can be indicated on a milliammeter which may be graduated in terms of time, speed, depth, &c. In the example shown in Figs. 1 and 3, passage of a vehicle interrupts the beam 1 from the source 3 to the photo-electric receiver 5 causing a decrease in the current in the relay 20 which allows the contact 20<1> to be made to actuate the relay 10 and pivoted armature 10<2> to break the contact 10<1> normally short-circuiting the condenser 8. The condenser 8, which is connected to the grid 14, is thus charged. through the battery 9, high resistance 12 and contact 11<1>. The connection of the negative plate of the condenser 8 to the grid 14 causes a decrease in the anode current which is indicated on the milliammeter 18. The condenser 8 is connected either directly to the negative end of the filament 15 or through a potentiometer 22 thus permitting the giving to the pertinent plate of the condenser a potential slightly more negative than that of the filament. Thus by a regulation of the cursor of-the potentiometer the anode current can always be brought to the same initial value when the condenser is shortcircuited. The charging of the condenser 8 and the decrease in the anode current takes place until the beam 2 is interrupted by the vehicle to cause a decrease in the current in the relay 21 to allow' the contact 21<1> to be closed and the relay 11 to be excited to attract its armature pivoted at 11<2> to break the.contact 11<1>, to interrupt the charging of the condenser 8 and the fall in the reading of the milliammeter 18 which remains constant for some time owing to the high insulation (of the order of 1,000 megohms) of the condenser, of the grid of the valve and of the connections. The relays 10, 11 are supplied by a source, 25 of sufficient voltage . to render their closure very rapid. The scale of the milliammeter can be changed by using one of a series of resistances 12 or one of a series of condensers 8. A circuit-breaker 26 allows the, simultaneous cutting of the supply 25 of the relays 10, 11 to bring them back to the starting position for a new measurement. A changeover switch 24A is provided. The arrangements constituted by the relays 10, 20 on the one hand and 11, 21 on the other are identically constituted so that the total lag introduced can be reduced. The closure of the contacts 13 through actuation of the relays 10, 11 maintains the current flowing through a resistance 28 or 29, limiting its value to that which permits the attraction of the armature without overheating, the relays 10, 11 remaining closed.