Patent GB-556341-A (GB)
Title: Improvements in or relating to electric measuring instruments
IPC: G01R11/56
Filed: 1942-06-04
Abstract: 556,341. Current and power measurements. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 4, 1942, No. 7604. Convention date, May 20, 1941. [Class 37] An energy meter includes a pair of thermal units actuating a shaft, means for heating these units, and a housing comprising a unitary heat insulating base provided with spaced chambers for receiving the thermal units and their heaters and detachable heat insulating covers for these chambers. Fig. 3 shows a time-lagged maximum demand indicator which, when subjected to a constant load, causes its pointer to move across the scale with a speed which diminishes in accordance with the time of deflection. Two bimetallic springs 16, 17 have their inner ends attached to hubs 18, 19 fixed to a common shaft 20 which carries a pusher arm (not shown). Each of the bimetallic springs is heated by a pair of heaters, one pair carrying a current proportional to the vector sum of the current and volts in the circuit and the other pair carrying a current proportional to their vector difference. The springs are arranged to act differentially on the shaft, the rotation of which is a measure of the power. The springs and heaters are enclosed in a housing which comprises a base portion 29 and caps 46, 47 and is constructed of a heat and electrical insulating material such as a phenol formaldehyde condensation product. Chambers 30, 31 are provided for receiving the bimetallic springs 16, 17, and slots 32, 33, 34, 35 are arranged to take the heaters. The chambers 30, 31 are separated by an air space 37 to reduce transmission of heat between them. The base 29 also has a slot 38a to receive the ring flange 38 of a bearing 39 for one end of the shaft 20. The other end of the shaft is journalled in a bearing carried by the face plate of the meter. The outer ends of the bimetallic springs 16, 17 are attached to split rings 41, 42 which are positioned in the chambers 30. 31 by ribs (not shown) which fit between the ends of the split rings. An air space is left between each split ring and the inner surface of its chamber by means of abutments 45 contacting with the split rings. The caps 46, 47 are provided with chambers and slots similar to those in the base 29. Each heater is substantially of U-shape having a channel 48 communicating with a central opening, in order to allow the shaft 20 to be removed without disturbing the heaters. Slits 49 may be formed for increasing the resistance of the heaters. Each heater is provided with projections 50 which project from opposite sides of the housing to serve as connecting lugs. Each heater is urged into intimate contact with the wall of the slot nearest to the associated bimetallic spring to facilitate heat transmission. Protuberances 51 are provided on the heater for this purpose. The heaters are made of a material having a high positive temperature coefficient. such as soft iron. The maximum demand indicator is mounted on a shelf behind the face plate of a supply meter, the pusher arm passing through a slot and operating a non-return pointer. An adjusting spring 67 acting on a lever 66 which is fixed to the shaft 20 by a set screw enables a standard scale to be used.