Daniel L Graham

US Patent:

50252208, Jun 18, 1991

Filed:

Sep 21, 1989

Appl. No.:

7/410772

Inventors:

Alex D. Colvin - Oak Park MI
Daniel J. Graham - Farmington MI
Joseph C. Cassatta - Taylor MI

Assignee:

Ford Motor Company - Dearborn MI

International Classification:

G01N 2702

US Classification:

324449

Abstract:

A method and apparatus for measuring the electrical conductivity of a liquid comprises an electrically insulating housing through which the liquid flows, and four electrodes inserted into the path of the liquid flowing through the housing. The first and third electrodes are current electrodes and the second and fourth electrodes are voltage electrodes. An AC current is injected into the first current electrode and exits at the second current electrode, with the resulting AC voltage across the voltage electrodes being measured. The first current electrode is driven to maintain a constant value of AC voltage on the voltage electrodes while measuring the current flow in the second current electrode which is representative of the electrical conductivity of the liquid. A DC bias voltage source is provided and is coupled to each of the electrodes by a resistor and a capacitor to prevent coating or plating of the electrodes. The method and apparatus permit continuous monitoring of the absolute conductivity of a liquid.