Patent ID: 8063644

Claim:
A method of measuring impedance of a pH electrode, the method comprising: applying a test current to the pH electrode for a time duration that is less than 50 percent of a time constant that is associated with electrical characteristics of the pH electrode wherein applying a test current includes applying a first test current to the pH electrode for a first time duration and applying a second test current to the pH electrode for a second time duration the second test current being substantially equal to but opposite in polarity to the first test current; measuring a voltage response comprising measuring a first voltage response when the first test current is applied to the pH electrode and measuring a second voltage response of the pH electrode while the second test current is applied to the pH electrode; calculating an impedance of the pH electrode as a function of the voltage response; determining whether the calculated impedance exceeds a maximum allowable impedance; and selectively generating a fault signal based upon the step of determining whether the calculated impedance exceeds the maximum allowable impedance; and calculating a source voltage of the pH electrode as an average of the first voltage response and the second voltage response, the source voltage being indicative of pH of a solution.