Ecolab Inc.

Charles B Johnson

Daniel F Brady

David B Ziegler

Spencer B Larson

The invention includes a method and apparatus for controlling the concentration of wash water in a ware washing machine. A preferred ware washing machine (10) includes a reservoir (11) for holding wash water, a normally closed valve (17) for directing clean water to a dry detergent supply (13), an electrodeless conductivity cell (12) for monitoring the conductivity of the ware washing solution, and a controller for activating the normally closed valve (15) in response to the difference between the measured concentration and the actual concentration. A preferred concentration controller includes an adjustable amplifier (48) which provides an amplified concentration signal which is equal to a reference signal when the concentration of the solution is equal to the desired concentration. In addition, a preferred conductivity cell (12) includes a thermistor (46) which, in effect, increases or decreases the voltage of the signal produced by the secondary coil to remove the apparent concentration changes solely associated with changes in temperature of the washing solution.

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Eagan, MN, United States of America

Charles B Johnson