Coulometric metering device

Abstract

Electric metering device including at least two coulometric cells which experience a sharp voltage rise upon deplating. The current is metered by passing current through one cell until it is deplated, whereupon the sharp voltage rise causes a second cell to become conducting. In a typical application, the cells would then be replaced and recharged for reuse.

We claim: 
     
       1. A device for metering electric current usage comprising: a current transformer having a primary winding for connection to a power line to be metered,   a full-wave rectifier including a center-tap secondary winding on the transformer, .Iadd.   a removable cartridge containing .Iaddend. at least two electro-plating coulometric cells, each of which initially has a known plating charge and experiences a sharp voltage rise upon deplating,   a switching device normally connecting only a first of said coulometric cells across the rectifier, which switching device is responsive to the sharp voltage rise in the first coulometric cell for connecting the second coulometric cell across the rectifier and for providing a perceptible indication thereof .Iadd.to warn that the cartridge needs to be removed to recharge the cells. .Iaddend.   
     
     
       2. A metering device as defined in claim 1 wherein the first coulometric cell is normally connected across the rectifier through a first resistance and the second coulometric cell is connected across the rectifier upon actuation of the switching device through a second resistance which is small relative to the first resistance so that the second coulometric cell is deplated at a faster rate than the first. 
     
     
       3. A metering device as defined in claim 2 and further including means for sensing the sharp voltage rise in the second coulometric cell and for thereupon interrupting current flow in a power line to which the device is connected. 
     
     
       4. A metering device as defined in claim 2 having two coulometric cells of equal capacity wherein the second resistance is at most one-tenth the first resistance so that the rate of deplating the second coulometric cell is at least ten times that of the first. 
     
     
       5. A metering device as defined in claim 1 wherein each coulometric cell consists of an anode, a cathode and a plating electrolyte, a known mass of which is initially plated on the anode, and each cell experience a sharp voltage rise when the electrolyte is deplated from the anode. 
     
     
       6. Method for metering electric current in a power line employing .Iadd.a device including a removable cartridge containing .Iaddend.at least two coulometric cells which experience a sharp voltage rise upon deplating, each of which initially has a known plating charge, comprising the steps of 1. initially shunting current from the power line through only a first of the coulometric cells,   2. sensing for the sharp voltage rise upon deplating of the first cell and upon so sensing,   3. shunting current from the power line through a second of the coulometric cells and providing a perceptible indication thereof .Iadd.to warn that the cells need recharging,   4. removing the cartridge from the device to apply a new known plating charge. .Iaddend..Iadd. 7. Method for metering electric current in a power line employing a device including a removable cartridge containing at least two coulometric cells, each of which initially has a known plating charge appied to one electrode and experiences a sharp voltage rise upon deplating, comprising the steps of   1. initially shunting current from the power line through only a first of the coulometric cells,   2. sensing for the sharp voltage rise upon deplating of the first cell and upon so sensing,   3. shunting current from the power line through a second of the coulometric cells and providing a perceptible indication thereof to warn that the cells will need recharging,   
     
     
       4.  replacing the spent cartridge with another charged cartridge, and 5. taking the spent cartridge to an agency for recharging. .Iaddend..Iadd. 8. A metering device as defined in claim 1 including another charged cartridge to substitute for said removable cartridge to permit said removable cartridge to be taken to an agency for recharging. .Iaddend.