Conductivity Counter

A conductivity measuring apparatus, comprising:

• a. a variable frequency current source;
• b. a sample cell electrically connected to the current source;
• c. an inductance electrically connected to the current source and in parallel with the sample cell, such that the sample cell and the inductance form the electrical equivalent of a parallel RLC circuit;
• and,
• d. a detector electrically connected to the sample cell.

An apparatus comprising:

• a. a fluid sample cell that can be modeled as an electrical circuit having a sample resistance in parallel with an effective cell capacitance;
• b. an inductance connected in parallel with the fluid sample cell, forming the electrical equivalent of a parallel RLC circuit having a resonance frequency;
• and,
• c. a frequency turnable current source connected to the fluid sample cell and the simulated inductor, wherein the current source has a frequency range broad enough to tune the current source to the resonance frequency of the equivalent parallel RLC circuit.

A method of calibrating a conductivity measuring apparatus, comprising:

• a. applying a variable frequency current source to a sample cell containing a buffer solution, wherein the sample cell is connected to an inductance to form a parallel RLC circuit;
• b. detecting the voltage amplitude across the parallel RLC circuit;
• c. varying the frequency of the current source while monitoring the voltage amplitude across the parallel RLC circuit to determine the resonance frequency of the parallel RLC circuit, which is indicated by the frequency at which the voltage has maximum amplitude;
• d. fixing the current source frequency at the resonance frequency of the parallel RLC circuit;
• and,
• e. nulling an output signal resulting from measurement of the buffer solution.

A method of counting small objects contained in a fluid sample, comprising:

• a. filling a sample cell with a buffer solution, the sample cell being connected in parallel with an inductance and forming an equivalent RLC circuit;
• b. applying a variable frequency current source to the sample cell and inductance;
• c. tuning the current source frequency to the resonance frequency of the equivalent RLC circuit;
• d. nulling the output of the equivalent RLC circuit;
• e. initiating a flow of test fluid through the sample cell, the test fluid containing the objects to be counted;
• and
• f. detecting changes in the conductivity of the sample cell as the objects pass through the sample cell.