452,374. Electric supply meters ; utilizing light radiations. DANCE, H. E., 79, Broad Street, Birmingham. Feb. 20, 1935, Nos. 5388 and 17134. [Class 37] In an electrical supervising apparatus for providing signalling and /or controlling operations for supervising the demand in electricity supply systems working on a two-part tariff, there are provided means responsive to the consumption of energy in successive integrating periods, means responsive to the maximum amount of energy consumed in any integrating period, and means for progressively comparing the actual value of the total consumption of energy from the commencement of each period with a value progressively increasing throughout the integrating period and corresponding to a constant consumption which at the end of this period corresponds with the previously established maximum value, and for causing the operation of signal and /or control means when the energy consumed in the expired portion of the present period is equivalent or approximately equivalent to the progressively increasing value. The demand meter or integrating mechanism 1 drives through a disengageable pinion 4, a spindle 6 which carries a pointer 7, and the latter in rotating moves a member 10, which assumes a position depending upon the maximum energy consumption during any integrating period. The meter 1 also drives through a gear 12 a spindle 14 carrying a pointer 15 and a contact 16 which is adapted to engage a contact 17 carried by the member 10. The contacts 16, 17 are in the circuit of a coil 18 which serves to move the gear 12 out of engagement with a gear 13 on the spindle 14 and permit the latter to return to its zero position. A coil 19 which is also energized when the contacts 16, 17 engage serves to operate a ratchet device 20 for stepping-on a shaft 21 connected to a part A of a differential 22, the second part B of which is driven from a synchronous motor or clock 25. The third part 30 of the differential carries a contact adapted to engage contacts 32 in the circuit of a signal- or control-operating relay 33. Resetting coils 9, 37, 39 for operating on the gear 4, the ratchet device 20, and a disengageable gear 28 in the drive to the part B of the differential, respectively, are provided to permit the spindle 6 and the differential parts A and B to return to zero positions at times determined by a rotary contact member 34 driven by the motor 25. In use, the pointer 7 returns at the end of each integrating period to its zero position and the pointer 10 assumes a position indicating the maximum demand during any individual integrating period. During any such period, the part B of the differential is rotated at a constant rate by the motor 25 while the part A is rotated in the opposite direction each time the contacts 16, 17 engage, the amount of this rotation being proportional to the consumption of energy from the commencement of the period and also upon the position of the member 10, which is fixed by the previously established maximum demand. If the movement of the part A exceeds that of the part B, the contacts 32 are closed and the signal relay 33 operated. In a modification, a meter disc which is provided with a black segment is illuminated, and the reflected light falls on a photo-electric cell which transmits impulses at a rate proportional to the energy consumption to a coil controlling an escapement device which at each impulse permits a motor to drive frictionally the part A of a differential mechanism. The part B is driven from a constant speed motor through a clutch which is energized for periods which are proportional to the previous maximum demand..This is obtained by means of an apertured, rotating disc and a photo-electric cell, which receives light reflected through the disc aperture from the surface of a second disc also provided with a black sector and which is rotatable so as to conceal part of the sector behind a stationary screen, the extent of the sector concealed being determined by the previous maximum demand. Alternatively, the scanning device can be replaced by conducting arcs, the relative positions of which depend on the previous maximum demand and which are bridged by a rotating arm. By this means, one side of the differential is driven at a speed proportional to the instantaneous demand while the other side is driven at a speed proportional to the previous maximum demand, so that, if the former exceeds the latter, the third part of the differential closes a switch operating the signal relay. Resetting coils are provided for the signal relay switch and for the device which adjusts the position of the maximum demand indicator. In a further modification, the connection between the shaft 14 and the differential is made by means of a photo-electric cell by providing screens on the element 10 and on the shaft 14, interposed between a light source and a photo-electric cell, such that light falls on the cell when the shaft 14 is rotated to a position corresponding with the displacement of the member 10. Alternatively, the spindle 14 may carry a disc having a reflecting sector which is normally concealed by a screen on the member 10 but is exposed when the shaft 14 is sufficiently rotated and causes the operation of a photo. electric cell. The integrating meter used may be of the Merz type or a thermal device wherein the heating effect of the electrical energy consumed operates on a thermostatic element. Specification 421,402 is referred to.