Patent GB-516338-A (GB)
Title: Improvements in or relating to electric methods of and systems for governing the recording or controlling action of an instrument
IPC: G01D9/16
Filed: 1938-03-22
Abstract: 516,338. Recording apparatus. TAGLIABUE MANUFACTURING CO., C. J. March 22, 1938, Nos. 8791 and 8792. Convention dates, March 22, 1937, and Feb. 25, 1938. [Glass 106 (iv)] [Also in Group XXXVIII]  In a system for recording or controlling the value of a variable more particularly of the type employing a selfbalancing. Wheatstone bridge circuit the recording or control element is operated only if the variable has maintained a uniform value for a predetermined time. As shown in Fig. 1, a self-balancing bridge circuit 42, which incorporates a galvanometer controlled photo-electric cell 138 for operating the balancing motor, controls recording apparatus 34 and is arranged to be switched successively into circuit with a plurality of thermocouples 41, by a step-by-step switch 40 operated by ratchet mechanisms 24, 26. The ratchet mechanism is stepped on by a continuously rotated cam 10 and levers 20, 22 only if the balanced condition of the bridge is maintained for a pre-' determined time interval, viz., for one revolution of the cam. The ratchet mechanism also 'controls the printing operation so that a record is printed only after the predetermined interval. The cam 10 comprises a cylinder 14, Fig. 3, having a disc-like projection provided with a notch 18 the surface of which gradually rises from surface 14 to a surface 16 which carries a pin 17. The lever 20 has a hooked end 19 which co-operates with the cam under the control of a lever 50 which is operated by a solenoid 47 associated with the bridge circuit. The arrangement is such that when the bridge is balanced motor control switches 41", 43" are open and the solenoid is de-energized to permit lever 50 under the pressure of springs 53 to maintain the end 19 of lever 20 in contact with the outer edge of the disc 16 and to permit the end 19 to enter the notch 18, Fig. 5, and move on to the surface 16. If then this condition is maintained for substantially one revolution of the cam the pin 17 engages the hook 19 and the lever 20 is lowered to rotate the pivoted lever 22 which through the pawl 24 steps the wheel 26 and switch 40. As soon as the wheel 26 moves a projection 37 falls between the teeth and printing is effected in according with the position of the balancing arm of the bridge Subsequently the switch 40 associates the next thermocouple with the bridge circuit. A roller 38 also raises the printing carriage after printing and resets the projection on the next tooth of the wheel. Finally the pin- 17 escapes from the hook 19 and theparts are restored under spring control  and the cycle is repeated. If a change of value is not maintained for the predetermined period the lever 20 is released before engagement with' the pin 17 and printing is not effected. In order to effect printing at regular intervals, the switches 43', 43" may be short-circuited by a manually operated switch 76 and a switch 71 which is periodically opened by cams 65 mounted on a ratchet wheel 64 driven at a slower rate than the cam 10 to place the recorder under the control of the switches 43<SP>1</SP>, 43<SP>11</SP> twice for each revolution of the ratchet wheel. The photo-electrically controlled balancing circuit is the same as that described in Specification 514,990, [Group XXXVIII], wherein the photo-cell controls a valve amplifier for the control relays of the balancing motor in such a manner that a change of cell illumination due to unbalancing produces a high rate of response in the output of the amplifier followed by a sharply reduced rate in order to prevent hunting about the balance point. Specification 512,984, [Group XXXVIII], also is referred to.