Constant alternating current conductivity detector for a chromatograph

摘要

A circuit is provided for producing an electrical output signal representative of the conductivity of a sample of fluid in a chromatograph sample cell. A constant A.C. current source is connected to one of the electrodes in the conductivity cell and a change in the resistivity of the cell is measured to produce an A.C. signal which is then conditioned by a signal conditioner. The signal conditioner scales the AC signal and converts it to a D.C. signal representing the resistivity of the conductivity cell. The resistivity signal is supplied to dividing means which is operable for inverting the resistivity signal to provide a signal representative of the conductivity of the sample fluid. Conductivity values can be detected in both the sample conductivity cell and a reference conductivity cell to provide conductivity signals for both the sample cell and the reference cell. These conductivity signals can be used for inputs into a difference amplifier to provide a signal representative of the difference between the two conductivity signals and its sign.