Patent GB-713762-A (GB)
Title: Improvements in and relating to apparatus for recording electric variations
Inventor: LARKBY GEOFFREY WALTER HENRY
IPC: G01R13/12
Filed: 1951-07-06
Abstract: 713,762. Recording-apparatus. LARKBY & SCOTT, Ltd. June 24, 1952,[July 6, 1951; Sept. 24, 1951], Nos 16119/51 and 22353/51. Class 106 (4). [Also in Group XL(c)]. Apparatus for recording electric variation comprises means for moving between and in contact with two electrodes a thin material of a kind which is marked on the passage of current therethrough and means to produce a potential gradient in one of the electrodes in a direction transverse to the direction of movement of the material, the arrangement being such that current sufficient to produce marking can flow in only one direction between the electrodes or that only current flowing in one direction produces a substantial mark, and means to apply electric variations to be recorded to vary the potential difference between the electrodes in such a manner that the current flow between the electrodes and through the material over a region on the material whose width varies in accordance with the electric variations. The embodiment of the invention described is applicable to recording signals in a system of navigation known as "Consul " wherein it is necessary to count the number .of dots and the number of dashes received in a cycle of. 60 lasting 40 seconds to obtain the bearing of the transmitting station, two such bearings giving a fix. As shown, Fig. 1, paper tape 10 from a drum 11 passes over a hinged rolller 12, under a rotatably-mounted recording cylinder 13 and under a roller 14 of resilient material, the rollers 13, 14 being geared together by: two pinions and driven by a clockwork or electric motor the drum 11 being suitably braked. The recording cylinder 13 comprises resistance wire 22, Fig. 4, wound on insulating material, the turns being insulated from one another, e.g. by an enamel coating and the crests of the turns presenting conducting surfaces to the paper tape 10, e.g. by removing the enamel. A thin ferrous metal electrode 23 is spring-pressed by its own resilience against the tape 10 toward the cylinder 13, extending over most of its width. The two ends of the winding on the cylinder 13 are connected to two slip-rings 24, 25 respectively with which contact is made by brushes 26, 27 connected to a source of direct current 28, Fig. 5, to provide a potential gradient across the cylinder 13. A voltage to be recorded is applied between the lower potential brush 26 and the electrode 23 in a sense to make the electrode 23 more positive. A suitable bias may be applied to ensure that the whole of the voltage variations to be recorded make the electrode more positive than the lower potential brush. When using the apparatus to record Consul signals obtained from a radio receiver 30 including a B.F.O. the beat note is rectified and the resulting voltage is applied directly in appropriate sense. The tape is one which marks only when current flows from a ferrous metal electrode to the cylinder, e.g. a paper containing an iron salt and known as " Muirhead Facsimile paper. Assuming that the lower potential brush 26 is earthed and that the other brush is maintained at 6 volts positive to earth by the battery 28, if the electrode 23 is made one volt positive to earth by a battery 29, current will flow from the electrode 23 to cylinder 13 over about one sixth of the width of the winding and, when the applied voltage is 3 volts the electrode 23 is 4 volts positive to earth and current will flow over about two thirds of the width of the winding. With a varying but uninterrupted applied voltage the form of record will be as shown in Fig. 3. A specially ruled protractor may facilitate counting the dots and dashes which may be extrapolated where they are indistinguishable. A humidifier 33 may be provided in the box 31. If a tape such as iodized paper tape is used which marks the current in either direction irrespective of the material of the electrodes, means must be provided to permit appreciable current flow in only one direction through the paper, e.g. a rectifier 36; Fig. 5, in series with the input to electrode 23 or if the voltage variations have a sufficiently high rate of change a condenser may replace the rectifier 36, the condenser being provided with a shunt leak resistance of sufficiently high value to prevent excessive current flow through the paper in the reverse direction to that desired. A rectifier may be used to ensure the flow of substantial current through the paper in the desired direction or a series impedance element may be used as e.g. a choke, offering a sufficiently high impedance to the alternating current. The winding on the cylinder 13 may be replaced by a continuous resistive element e.g. it may be of carbon or of ceramic material coated with a thin layer of metal such as platinum. If desired the driving roller 14 may act as one electrode and may be spring-pressed against the cylinder 13. It may then be formed either as a metalcylinder or it may be built up of a number of spaced metal discs. Alternatively the electrode 23 may be formed as a comb, reducing the area of contact thus increasing the local current density and decreasing friction. In, order to record the time at which a record is made the e'ectrode 23 extends over only part of the width of the recording cylinder 13 and a further insulated electrode 44 is arranged to contact the paper alongside the first and is in series with a switch 45 and voltage source 46. The switch 45 is pressed at some time during recording to produce a mark 47 on the tape and is followed by code markings indicating the time which may be produced by a Post Office telephone dial 49 modified so that contact is made instead of broken thereby. The apparatus may be used on a vehicle to fix its position by marking successive recordings of signals from two Consul stations but if the vehicle were travelling fast the time interval between the recordings would cause considerable error. A simultaneous recording from any two stations may be obtained on a single strip with apparatus comprising a recording cylinder with a winding whose ends are connected to. slip rings and thence by brushes to a direct current source- 28, Fig. 13, and whose centre is tapped and connected to earth either through a slip ring or through the cylinder shaft, so that two potential gradients are set up across the winding. A centre electrode 44 is provided for time marking and two electrodes 23, 52 connected to separate radio receivers one tuned to each of two stations receive recording voltages so that two records are produced as shown in Fig. 14. A more practical circuit arrangement is shown in Fig. 13 wherein the two electrodes 23, 52 are connected to the two output terminals of a high-speed, two-way relay 54 whose input terminal is connected to the output stage 30D of a radio receiver. The relay 54 is operated in synchronism with a similar relay 55 by means of a common A.C. power source 56 operating at, say, 50-60 cycles per second. The response of the R.F. stage 30A is broad enough to be able to amplify signals from five stations and the appropriate station is selected by adjusting the frequency of the oscillator stage 30B which is provided with five variable capacitors A, B, C, D and E, each of which is connected to two five-position switches 57 and 58 whose rotors are connected to the two input terminals of the relay 55, the output terminal being earthed. The switch 57 is set to put the capacitor D in circuit and the switch 58 the capacitor B and the relays 55, 54 are set so that with the capacitor D in circuit the radio receiver is tuned to receive signals from the respective station and the voltage to be recorded is applied to electrode 52, while with the capacitor B in circuit the recording voltage is applied to the electrode 23. Switching means other than two A.C. operated mechanical relays may be used, e.g. D.C. operated mechanical relays or electronic relays comprising crystal or thermionic diodes to which appropriate switching voltages are applied.