Patent GB-556344-A (GB)
Title: Novel or improved means for recording the frequency of alternating electric current supply
IPC: G01R13/04
Filed: 1942-06-10
Abstract: 556,344. Frequency measurements. MARGARY, T. A. G. June 10, 1942, No. 7895. [Class 37] [Also in Group XIX] A cylindrical drum is rotated at a speed proportional to the frequency to be recorded and is marked by an axially moving stylus at equal time intervals corresponding to an integral number of revolutions of the drum when the frequency has its standard value. As shown in Fig. 1 a cylindrical drum 1 with which cooperates a movable stylus 2 is arranged to be driven by a synchronous motor 3 through a reducing gear train 4. The drum may carry a paper sheet and the stylus may be an inking pen or pencil. The stylus 2 is resiliently attached to a nut 5 which is moved by a gear-wheel 7 from the train 4. The screw 6 is mounted so as to permit a small axial motion against the bias of a spring 10 when an armature 12 is attracted by a solenoid 13. This imparts a short quick movement to the stylus in the axial direction of the drum and causes it to make a mark on the chart. Energization of the solenoid 13 is effected at successive equal time intervals by means of a standard clock 14. The motor 3 is driven from a supply system of which the frequency is to be recorded, or from an alternator driven at a speed proportional to the speed of an object, which speed is to be recorded. The solenoid 13 may be energized at half-minute intervals and the chart rotated at two revolutions per minute when the frequency has its intended normal value. If the frequency remains constant marks are made on the chart along the same axial line, deviation from this line indicating the extent and direction of changes of frequency. In a modification, Fig. 3, the drum 1 is biased by means of a spring t 5 to return to a zero position determined by a stop 16 when it is disconnected from the motor 3 by means of a magnetic clutch 17 controlled by the clock 14. The screw 6 is driven through ratchet gear 18 or other free-wheel device so as to remain at rest when the drum 1 is being returned to its zero position. The stylus 2 is normally held out of engagement with the chart by a spring so that an arm 21 carried bv the nut 5 rests on a flat strip 22 which has cylindrical ends mounted in bearings 23, 24. The strip is rocked by an electromagnet 26 controlled by the clock 14 so as to bring the stylus 2 into contact with the chart slightly before the end of the time interval. The clock 14 is adjusted to operate the clutch 17 at the ends of equal periods of time, for example periods of ten minutes. During each period the drum is rotated through, for example. five revolutions. Just prior to the end of the period the electromagnet 26 is energized and causes the stylus 2 to initiate a mark on the chart. At the end of the period the clutch 17 is released and the drum 1 is returned to zero nosition with simultaneous release of the stylus. the screw 6 remainine at rest until the next cvcle of operation is started bv the clock. for instance after fifteen minutes from the previous start. The stvlus may alternatively be in the form of a silver or other soft metal member marking a chart which has a smoke-covered surface.