Patent ID: 7431886

Claim:
A method of monitoring operational status of sensing devices for determining a concentration of a chemical component in a fluid, comprising the steps of: sensing a first physico-chemical property of the chemical component by measuring a first electrical signal produced by a first sensor; determining a first concentration of the chemical component by referencing the first electrical signal to a first set of stored data; sensing a second physico-chemical property of the chemical component by measuring a second electrical signal produced by a second sensor, wherein the first physico-chemical property is different from the second physico-chemical property; determining a second concentration of the chemical component by referencing the second electrical signal to a second set of stored data; comparing the first concentration to the second concentration to determine whether the first concentration falls within a pre-set percentage of the second concentration; and determining that at least one of said first and second sensors is defective if the first concentration falls outside the pre-set percentage of the second concentration.