Conductivity measuring apparatus

• US 3,909,709 A
• Filed: 04/04/1974
• Issued: 09/30/1975
• Est. Priority Date: 04/04/1974
• Status: Expired due to Term

• Current Assignee: Leroy J. Maxon
• Original Assignee: Leroy J. Maxon
• Inventors: Maxon, Leroy J.
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/458,058
• Time in Patent Office: 544 Days
• Field of Search: 324/3R,3B,65R 204/242
• US Class Current: 324/442
• CPC Class Codes: G01N 27/06 of a liquid involving electrolysis G01N27/26

Abstract

An apparatus for measuring the conductivity of an element includes an oscillator which develops an a.c. signal. The oscillator circuit includes the primary winding of a transformer. The secondary winding of the transformer is a.c. coupled to a sensor. The sensor is constructed to be placed in contact with the element whose conductivity is to be measured. The element whose conductivity is to be measured is also placed in contact with a reference potential. This reference potential is also applied to portions of the apparatus. The element completes a conductive a.c. path between the sensor and the reference potential. The a.c. path conductivity is equal to the conductivity of the element. The transformer secondary winding has an a.c. signal induced thereacross from the transformer primary which varies in accordance with the conductivity of the path provided by the sensor and element. A meter coupled to the transformer operates in response to the amplitude of the induced a.c. signal to indicate the conductivity of the element.

Claims

1. An electrical apparatus for measuring variations in conductivity of an element having a first conductivity wherein said variation is due to the presence, type and amount of a material in said element having a second conductivity, said element being contained in an electrically conductive container, said apparatus comprising:

a shielded cable, the electrical shielding thereof adapted to electrically connect said electrical apparatus ground to said container, an oscillator for generating an AC signal;

coupling means coupled to said oscillator for developing a reference potential in response to said AC signal, said coupling means including a voltage limiting network comprised of a plurality of parellel rectifier circuits each comprised of a plurality of rectifiers and adapted to provide failsafe voltage limiting of said reference potential to 1.4 volts peak to peak;

sensor means electrically connected to said reference potential via said shielded cable, said sensor means being constructed and arranged to be placed in contact with said element, said element completing a conductive path between said container and said reference potential via said sensor means, said path conductivity varying in accordance with said variations in conductivity of said element;

means responsive to said variations in conductivity for creating an amplitude varying signal;

indicator means responsive to said amplitude varying signal and adapted to indicate said variations in conductivity of said element;

test means including a resistance and means for selectively disconnecting said sensor means from said reference potential and connecting said resistance to said reference potential whereby a predetermined potential is applied to said means for creating said amplitude varying signal; and

variable resistance means for adjusting said predetermined potential.

2. An electrical apparatus for measuring variation in conductivity of an element having a first conductivity wherein said variation is due to the presence, type and amount of material having a second conductivity in said element, said apparatus comprising:

a first and second terminal for connection to a source of potential having a first reference potential and a second source of potential, said first reference potential being in contact with said element;

oscillator means coupled to said first and second terminals and operative in response to said source of potential to develop an AC signal;

a transformer having a primary and secondary winding, said primary winding coupled with said oscillator means and having a portion of said AC signal developed there across, said secondary winding having third and fourth termiNals;

sensor means AC coupled to said secondary windings, said sensor means constructed and arranged to be placed in contact with said element, said element completing a conductive AC path between said sensor means and said first reference potential, the AC path conductivity varying in accordance with said variation in conductivity of said element, said transformer secondary inducing a first AC signal there across having an amplitude which varies in accordance with said variation in said AC path conductivity;

means for limiting the peak to peak excursions of said first AC signal to a value below that required for sparking in an explosive atmosphere, said value being 100 milliamps; and

indicator means in circuit with said transformer secondary and operative in response to said first AC signal to indicate the variation in conductivity of said element.

3. The apparatus of claim 1 wherein said coupling means includes an input for receiving said a.c. signal, said coupling means having an output terminal, a reference terminal and impedance means therebetween, said coupling means developing said first signal at an output terminal, said sensor means being a.c. coupled only to said impedance means.

4. The apparatus of claim 3 wherein said oscillator means includes, a transformer primary winding and said coupling means includes a secondary winding of said transformer, said secondary winding having a first and second terminal for developing a first a.c. signal thereacross in response to said oscillator a.c. signal, said transformer secondary winding first terminal being coupled to said coupling means reference terminal, said a.c. signal varying in amplitude in accordance with said variation in said path conductivity.

5. The apparatus of claim 4 wherein said coupling means further includes, amplifier means coupled to said transformer secondary winding second terminal and to said output terminal and operative in response to said first a.c. signal to develop said first signal, said first signal being a first current which varies in amplitude in accordance with said variation in conductivity of said element, said indicator means including a current meter coupled to said output terminal and operative in response to said first current to indicate said variations in said element conductivity.

6. The apparatus of claim 4 wherein said coupling means further includes, limiter means coupled to said transformer first and second terminals for limiting said first a.c. signals to a maximum amplitude, voltage doubler means coupled to said second terminal for doubling said first a.c. signal, amplifier means coupled to said voltage doubler means and said output terminal and operative in response to said doubled first a.c. signal to develop said first signal and couple same to said output terminal, said first signal being a first current which varies in amplitude in accordance with said variations in conductivity, said indicator means including a current meter coupled to said output terminal and operative in response to said first current to indicate said variations in said element conductivity.

7. The apparatus of claim 6 wherein said amplifier means includes, a transistor having base, emitter and collector electrodes, said base electrode being coupled to said voltage doubler means, said emitter electrode being coupled to said current meter, said collector electrode being coupled to a source of potential, said amplifier means being rendered conductive and conducting current from said collector to emitter electrodes in accordance with the amplitude of said signal coupled to said base electrode.

8. The apparatus of claim 1 wherein said variations in conductivity in said element and said variations in said path conductivity are variations in impedance, said coupling means being operative in response to said variations in impedance to vary the amplitude of said first signal, said indicator means operative in response to said variations in amplitude of saiD first signal to indicate said variations in conductivity of said element.

9. The apparatus of claim 8 further including electrolysis means selectively coupling said coupling means to said sensor means for inhibiting electrolysis of said sensor means in contact with said element.

10. The apparatus of claim 9 wherein said electrolysis means includes diode means coupled to said coupling means and selectively coupled to said sensor means.

11. The apparatus of claim 9 wherein a coupling capacitor a.c. couples said sensor means to said coupling means and further including switching means for selectively coupling one of said coupling capacitor and said electrolysis means to said sensor means whereby said a.c. signal through said coupling capacitor and said d.c. signal through said diode inhibit electrolysis.

12. The apparatus of claim 2 further including, signal limiting means coupled between said secondary winding third and fourth terminals for limiting said first a.c. signal amplitude, voltage doubler means coupled to said transformer secondary winding fourth terminal and operative to develop an amplitude doubled first a.c. signal in response to said first a.c. signal, amplifier means coupled to said voltage doubler means and operative in response to said amplitude doubled first a.c. signal to develop a first signal varying in accordance with said amplitude doubled first a.c. signal, said indicator means being coupled to said amplifier means and operative in response to said first signal to indicate said variation in conductivity of said element.