Developer apparatus having mass sensor for an electrographic printer or copier

A developer apparatus for use in an electrographic image transfer unit having a photoconductor with a latent charge image thereon, said developer apparatus comprising:

• a toner acceptance surface having a toner layer thereon, said toner layer having a layer thickness, a toner mass, a toner potential and a toner charge, said toner acceptance surface being spaced by a gap from said photoconductor and transporting said toner layer through said gap for depositing toner from said toner layer on said latent charge image;
• a capacitive mass sensor which identifies said toner mass by measuring said layer thickness, said capacitive mass sensor having a first electrode comprising at least a portion of said acceptance surface and a second electrode spaced from said acceptance surface, with said toner layer disposed between said first and second electrodes;
• a potential sensor which measures said toner potential;
• and an evaluation unit supplied with said toner mass from said capacitive mass sensor and said toner potential from said potential sensor for calculating said toner charge from said toner mass and said toner potential.