Abstract: Toner (5) is measured in a toner cartridge (1) by compressing the air in the upper part (7) of the toner hopper (3). The result of the compression is observed by a diaphragm (13) or, alternatively, by a pressure transducer (25). The volume of air is inversely proportional to the resonant frequency of diaphragm (13) or the pressure at pressure transducer (25). This is converted by control system (23) using direct equations or table look-up of empirical data. The diaphragm (13) carries a magnet (15), which is driven by coil (19) from the imaging device and then frequency of current induced by magnet (15) is then sensed by coil (19). Uneven toner piling is not a significant factor in the results measured.

Abstract: An improved electrophotographic (EP) printer is provided having a detachable process cartridge that contains a non-volatile memory device, which is an EPROM that cannot be erased after a bit is burned. A "toner wheel" mounted to the exterior of the toner reservoir of the process cartridge provides, in conjunction with an optoelectronic sensor, an electrical signal that the printer receives and uses to determine toner usage. A toner "gas-gauge" is created which uses "bucket levels" as discrete steps to indicate how much of the measured physical toner material actually remains within the toner reservoir. After a given amount of toner material has been dispensed through the developer unit, one of the bits of the EPROM memory device is irreversibly burned, thereby providing a permanent record on the process cartridge of a certain amount of toner usage.