Patent GB-618541-A (GB)
Title: Improvements in or relating to instruments for indicating the operating time of vehicles and other devices
IPC: G06G3/08
Filed: 1946-08-30
Abstract: 618,541. Registering running or flying times. NORRIS, G THORNTON-. Aug. 30, 1946, No. 26207. [Class 106 (iv)] [Also in Group XVIII] An instrument for indicating the operating time of a vehicle or other device comprises time-indicating means, an oscillatory chronometric balance which drives the time-indicating means, electrical means for maintaining the balance in oscillation, a main switch which is closed during the operating period for rendering the maintaining means operative, and a starting device comprising an auxiliary switch which is closed temporarily to start the balance and causes an augmented driving force to be exerted on said balance for setting it into oscillation. As applied to an aircraft the instrument comprises an electrically driven clock movement 26 installed on the instrumentboard and having a chronometric balance wheel 27 maintained in oscillation by an iron armature 28 swinging in the gap 30 of an iron core 31 intermittently energized by a coil 32. When running, current to the coil 32 is controlled by a plate 38 co-operating with a pin 39 electrical contact being made during the first part of each forward swing and broken just before the armature 28 is centred in the gap 30, the contact being insulated on the return swing. A spring pawl 50 on the armature 28 drives a ratchet wheel 51 and through gear train 54, 55, a spindle 53 upon which is frictionally mounted a sleeve 56 carrying a hand moving over a dial graduated in minutes, counters 14, 15 registering completed hours. To effect resetting, a knob 18 controlling a gear-wheel 68 and cooperating with a bell-crank lever 66 is moved in to engage a gear-wheel 60 on the sleeve 56 causing the bell-crank lever 66 to disengage the drive to the counter 15 so that the " trip " counter 14 can be reset and the hand zeroised. When the aircraft engines are switched on, a master switch 84 is closed and when sufficient pressure builds up in a capsule . 22 contacts 80, 82 of a main switch close and current from a battery 85 or other source flows through contacts 79, 81 of an auxiliary switch to the coil 32 to set the balance wheel in oscillation. The joint closing of the switches is very brie as the closing of the main switch soon lifts contact 79 away from contact 81 so that current thereafter flows to the coil 32 through a resistance 83, and is controlled by the contacts 38, 39. As the pressure falls at the end of each operating period, the auxiliary switch closes a brief time before the main switch opens and current byepassing the resistance 83 provides a momentary strong energization of the electromagnet to attract the armature 28 and damp out oscillations. In lieu of a resistance coil 83 the coil 32 may be tapped at an intermediary point. The capsule 22 may communicate with any convenient pressure source such as the pitot head of the air speed, indicator or the pressure lubricating system or the main switch may be actuated by the retraction and extension of the undercarriage, whereas in a vehicle or machine a centrifugal or other rotary device may be used.