Method and system for measuring water hardness

Abstract

Prior to adding detergent or chelant, the conductivity of water in a washing chamber is measured. The maximum concentration of hard water ions that could correspond to the 5 measured conductivity is determined, i.e., it is assumed that all of the conductivity is from calcium and/or magnesium ions in the water even though other ions may in fact be contributing to the measured conductivity. Enough chelating agent is added to the chamber to sequester this maximum concentration of hard water ions and the conductivity is measured again. Using the two conductivity measurements, the actual concentration of hard water ions 0 is determined. A chelant factor based on the actual concentration of hard water ions is then used to determine the amount of chelant to be added for subsequent wash cycles to sequester all of the hard water ions.

Description

technical field [0001] The invention mainly relates to the measurement of water hardness, especially the measurement and replenishment of water hardness in washing machines. Background technique [0002] Machine washing systems typically use detergents that are mixed with water to form a cleaning solution. Cleaning agents such as stain removers break down and remove food or other stains and are more effective in alkaline conditions. However, the presence of hard water ions (eg, calcium and magnesium ions) in the water can reduce the effectiveness of detergents. Therefore, chelating agents are added to the wash water to chelate hard water ions. Typical chelating agents include, but are not limited to, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and tripolyphosphate (TPP). [0003] Before the washing operation, the water hardness (ie, the concentration of hard water ions) is generally unknown, so the amount of chelating agent that needs to be added ...

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