Patent GB-803092-A (GB)
Abstract: 803,092. Maximum demand meters. TELEFONAKTIEBOLAGET L. M. ERICSSON. Sept. 10, 1956 [Sept. 8, 1955], No. 27681/56. Class 106 (3). A maximum demand meter comprises a graduated drum 11 advanced against the action of a spring 12, exerting a force proportional to the displacement of the drum, and restrained against return movement by a pawl 14 and ratchet 13, and a gate 15, 10, in one state permitting a meter-driven wheel 1 to drive the drum 11 and in another state preventing it, the state of the gate being determined by the direction of unbalance between the opposed forces of the spring 12 and a retarding force proportional to the instantaneous value of the quantity in demand. In the embodiment of Fig. 1, the drum 11 is secured to the planet carrier 7 of a differential gear, whose sun wheel 3 is driven from the meter shaft 6 through gearing (not shown) and whose sun wheel 8 is secured to the gate member 10, in the form of a ratchet wheel co-operating with a wheel 15 having a single tooth. The wheel 15 engages the wheel 10 when the rotor 26 of the meter rotates in the air gap 22b between one arm of a ferromagnetic yoke 22 and a permanent magnet 22a carried by its other arm and thereby urges the yoke 22 against one stop. While the speed of the shaft 6 is greater than that corresponding to the value indicated by the drum, the eddy current braking effect will be stronger than the reaction due to the spring 12, and the tooth of the wheel 15 will lock the ratchet 10, so that the planet carrier will progress round the stationary sun wheel 8 and, if this speed is maintained long enough, the pawl 14 will engage the next tooth of the ratchet 13 corresponding to the next graduation of the drum 11 and so on, at the same time winding the spring 12 until the force of the ratchet 10 against the tooth of wheel 15, due to the spring, counteracts the effect of the braking force and causes the tooth to move clear of the ratchet 10 and the yoke 22 to swing against another stop, only to be swung back by the braking face. While the wheel 15 thus oscillates, the sun wheel 8 is free and so prevents the advance of the drum 11, which continues to indicate the maximum value which has been maintained long enough to register. With a uniformly toothed ratchet wheel 13 and graduated disc 11 and spring with rectilinear characteristic the time a value has to be maintained in order to register is inversely proportional to the value. For uniform time intervals the ratchet teeth and graduations are spaced at intervals in arithmetic progression and a spring of suitable characteristics is required. If low values can be ignored, a good compromise to equal intervals can be obtained with a spring of rectilinear characteristic, if the spacing of the teeth and graduations is varied slightly from arithmetic progression. Two modifications to the gate and drive mechanisms are described with reference to Figs. 4 and 6 (not shown) and the invention may be applied to electricity meters, liquid flow meters or speedometers. It may also be applied to register the maximum number of parts produced per minute providing the corresponding capacity of a machine is maintained to produce say 100 parts, by interrupting a light beam impinging on a photo-electric cell which regulates supply of current to a meter.