Toner concentration sensing with self calibration

A method for calibrating an electrographic printing device, said printing device having a plurality of color toners, each of said color toners having a known concentration C.sub.0, said printing device having a flow cell where each color toner passes through, said flow cell having at least one windowing area for measuring transmissivity of each of said toners passing through said window, said printing device having memory for storing results of the calibration, said results being stored in a C1 look-up table and a C2 look-up table, including the steps of:

• requesting calibration;
• measuring a clear voltage value Vc for each of said windowing areas while passing a clear dispersant through said windowing area;
• measuring a voltage value V for each of said color toners while passing each of said toners through said windowing area;
• determining a low voltage limit for said clear voltage for each of said windowing areas;
• placing said low voltage limit in said C2 look-up table as a low voltage endpoint;
• determining a high voltage limit for said clear voltage for each of said windowing areas;
• placing said high voltage limit in said C2 look-up table as a high voltage endpoint;
• calculating .epsilon.x for each of said color toners using said clear voltage value Vc, where .epsilon. is an optical absorption coefficient of toner, and x is a thickness of said windowing areas, said voltage value V and said known concentration C.sub.0 ;
• calculating a clear voltage step size for said C2 look-up table;
• calculating remaining clear voltage values for said C2 look-up table;
• calculating a C2 concentration value for each of said clear voltage values in said C2 look-up table;
• determining a voltage range for each of said color toners, said voltage range being determined by an allowable range of concentrations for each of said toners, as well as said high and said low clear voltage limits;
• determining a low C1 concentration limit for each of said color toners;
• determining a high C1 concentration limit for each of said color toners;
• placing said high C1 concentration limit in said C1 look-up table as a high C1 concentration endpoint for each of said color toners;
• calculating a C1 concentration step size for said C1 look-up table for each of said color toners;
• calculating remaining C1 concentration values for said C1 look-up table for each of said color toners;
• calculating a concentration voltage V corresponding to said C1 concentration values for each of said toners in said C1 look-up table;
• and
• placing said C2 table and said memory to be used by said printing device to measure toner concentration.

A method for measuring concentration of toner particles carried in a fluid medium in an electrographic printing device, said printing device having a plurality of color toners, said printing device having a flow cell where each color toner passes through, said flow cell having at least one windowing area for measuring a voltage of each of said toners passing through said window, said printing device having memory for storing results of a calibration, including the steps of:

• a) generating a C1 look-up table and a C2 look-up table during a calibration cycle of said printing device, said C1 table having color voltage values and corresponding color concentration values for each of said color toners, said C2 table having clear dispersant voltage values and corresponding clear dispersant concentration values, said C1 table and said C2 table being stored in said memory;
• b) measuring transmissivity of clear dispersant through said flow cell resulting in a clear voltage value;
• c) reading a clear dispersant concentration value from said C2 table corresponding with said clear voltage value;
• d) measuring the transmissivity said color toner through said flow cell resulting in a toner voltage value;
• e) reading a color toner concentration value from said C1 table corresponding with said toner voltage value;
• f) adding said clear dispersant concentration value to said color toner concentration value resulting in a total concentration value;
• g) using said total concentration value to adjust the concentration of material in said fluid medium corresponding to said color toner;
• and
• repeating steps b through g for each of said color toners in said printing device.

A system for measuring concentration of a material carried in a fluid medium, comprising:

• a flow cell through which said fluid medium passes for measuring properties of a fluid medium passing through said flow cell;
• a first delivery system for delivering a first fluid containing material carried in fluid medium;
• a second delivery system for delivering a clear dispersant fluid;
• a switch for selecting among said delivery systems, said switch connecting one of said delivery systems to said flow cell;
• a generator for creating a table of C1 concentration and associated voltage values corresponding to the property measured of said first fluid through said flow cell, said table of C1 concentration and associated voltage values being derived during self calibration of said system;
• a generator for creating a table of C2 concentration and associated voltage values corresponding to the property measured of said clear dispersant through said flow cell, said table of C2 concentration and associated voltage values being derived during self calibration of said system;
• a first memory for storing said table of C1 concentration and associated voltage values;
• a second memory for storing said table of C2 concentration and associated voltage values;
• and
• an adder for summing a C1 concentration value from said C1 table with a C2 concentration value from said C2 table thereby determining said concentration of said material in said fluid medium being measured by said system.