Monitoring ink supply in ink printer - using metallic sensor changing magnetic field induced by ring coil

摘要

The monitor operates practically independently of external influences and provides a continuous exact indication. A magnetic field is produced in the ink in the container by a ring coil (4) encircling the container (3). A sensor (5) changes position according to the level in the ink container. The change in sensor position causes a cange in the magnetic field which is used as a monitoring criterion for the ink supply. The sensor, which is placed in the upper section of a flexible ink container, may be of metal. It may be of a material whose relative permeability differs from unity, e.g. of ferrite material. The ring coil may form part of an oscillator circuit.