Conductivity monitoring system

• US 3,953,790 A
• Filed: 02/05/1975
• Issued: 04/27/1976
• Est. Priority Date: 10/31/1974
• Status: Expired due to Term

• Current Assignee: Baxter Laboratories, Inc. (Baxter International Inc.)
• Original Assignee: Baxter Laboratories, Inc. (Baxter International Inc.)
• Inventors: Ebling, Wendell V., Goldsmith, Herbert
• Primary Examiner(s): Rolinec, R. V.
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/547,320
• Time in Patent Office: 447 Days
• Field of Search: 324/30 R, 324/30 B, 204/250, 204/274
• US Class Current: 324/446
• CPC Class Codes: G01N 27/10 Investigation or analysis specially adapted for controlling or monitoring operations or for signalling
• CPC Class Codes: G01R 27/22 Measuring resistance of fluids

Abstract

A conductivity monitoring system which includes at least three electrodes disposed within a housing of a conductivity cell, into and through which a fluid to be monitored is caused to flow. One of the electrodes is a common electrode and is positioned closer to one of the other two electrodes. The conductivity is measured between the wide spaced pair of electrodes and between the closer spaced pair of electrodes, with the difference being taken as the actual conductivity. With this arrangement, changes in the conductivity as a result of foreign matter collecting on the electrodes and the housing over a period of time are compensated for, since the difference in the conductivity between the two pairs of electrodes remain the same, even though the conductivity between each respective pair may change.

Claims

1. A conductivity monitoring system for continuously monitoring the conductivity of a fluid flowing into and through a housing comprising:

a. indicator means

b. at least a common, a first and a second electrode disposed within said housing in contact with said fluid, said common electrode being positioned closer to said first electrode than to said second electrode, whereby the electrical conductivity between said common electrode and said first electrode will be different than the electrical conductivity between said common electrode and said second electrode;

c. means connected to said electrodes to approximate a constant current source for energizing said electrodes to provide substantially the same current flow through them.

d. means for detecting the difference in the conductivity between said common and first electrodes and between said common and second electrodes and providing a difference voltage output signal representing the value of the conductivity of said fluid; and

e. means for coupling said signal to said indicator means to operate said indicator means.

2. The conductivity monitoring system of claim 1, comprising

a. a first transformer having a primary and a secondary winding, said common electrode being coupled to one terminal of said secondary winding and said first and second electrodes being coupled to the other terminal thereof;

b. a first and a second resistance means connected in series in said coupling between said other terminal of said secondary winding and said first and second electrodes, respectively; and

c. said means for energizing said electrodes being coupled to said primary winding.

3. The conductivity monitoring means of claim 2, wherein said means for energizing said electrodes comprises an oscillator means.

4. The conductivity monitoring means of claim 3, comprising a second transformer having a primary and a secondary winding, said primary winding thereof being connected across said first and second resistance means to thereby detect the difference in the conductivity between said common and first electrode and between said common and second electrode, said secondary winding providing said difference voltage output signal representing the value of the conductivity of said fluid.

5. The conductivity monitoring system of claim 1, further comprising:

a. temperature sensing means disposed within said housing for providing an output signal representative of the temperature of said fluid flowing into and through said housing

b. summing means responsive to said output signal from said temperature sensing means and said difference voltage signal representing the value of the conductivity of said fluid to provide a temperature compensated conductivity output signal;

c. means for coupling said two signals to said summing means; and

d. means for coupling said temperature compensated conductivity output signal to said indicator means.

6. The conductivity monitoring system of claim 5, wherein said temperature sensing means comprises a thermistor.

7. The conductivity monitoring means of claim 4, further comprising:

a. temperature sensing means disposed within said housing for providing an output signal representative of the temperature of said fluid flowing into and through said housing

b. summing means responsive to said output signal from said temperature sensing means and said difference voltage signal representing the value of the conductivity of said fluid to provide a temperature compensated conductivity output signal;

c. means for coupling said two signals to said summing means; and

d. means for coupling said temperature compensated conductivity output signal to said indicator means.

8. The conductivity monitoring system of claim 7 wherein said indicator means comprises meter means for providing thereon a reading representing the value of the conductivity of said fluid.

9. The conductivity monitoring system of claim 7 wherein said indicator means comprises a high and a low conductivity alarm means, each of which comprises comparator means for comparing the value of said conductivity signal with a preestablished high level and low level value, respectively, and providing an output signal to activate alarm means in the event the value of said conductivity signal is greater or less than said high level and low values, respectively.

10. The conductivity monitoring system of claim 9 wherein said indicator means further comprises meter means for providing thereon a reading representing the value of the conductivity of said fluid.

11. The conductivity monitoring system of claim 7 further comprising:

a. phase correcting means for removing harmonic distortions from said temperature compensated conductivity output signal to provide an AC output signal which is proportional in time the value of conductivity;

b. sample and hold means for sampling said AC output signal; and

c. means responsive to said sampled AC output signal for coupling a DC signal proportioned to the value of conductivity to said indicator means.

12. A conductivity monitoring system for monitoring the conductivity of a fluid flowing into and through a housing comprising:

a. indicator means;

b. at least a common, a first and a second electrode disposed within said housing in contact with said fluid, said common electrode being positioned closer to said first electrode than said second electrode;

c. a first and a second resistance means connected in series with said first and second electrodes, respectively;

d. a first transformer having a primary and a secondary winding, said common electrode being coupled to one terminal of said secondary winding and said first and second electrodes being coupled to the other terminal thereof;

e. a second transformer having a primary and a secondary winding, said primary winding being connected across said first and second resistance means to thereby detect the difference in conductivity between said common and first electrodes and said common and second electrodes and to provide at the output of said secondary winding a difference voltage signal representing the value of the conductivity of said fluid;

f. oscillator means coupled to said primary winding of said first transformer means for energizing said electrodes; and

g. means coupled to said secondary winding of said second transformer means and responsive to said difference voltage signal for providing a signal proportional to the value of the conductivity of said fluid to said indicator means to thereby operate the latter to provide an indication of the value of the conductivity of said fluid.

13. The conductivity monitoring system of claim 12, further comprising:

a. temperature sensing means disposed within said housing for providing an output signal representative of the temperature of said fluid flowing into and through said housing;

b. said means coupled to said secondary winding of said second transformer means including means responsive to said difference voltage signal and said output signal from said temperature sensing means to provide a temperature compensated signal proportional to the value of the conductivity of said fluid to said indicator means.

14. The conductivity monitoring system of claim 13 wherein said indicator means comprises meter means for providing thereon a reading representative the value of the conductivity of said fluid.

15. The conductivity monitoring system of claim 13 wherein said indicator means comprises a high and a low conductivity alarm means, each of which comprises comparator means for comparing the value of said conductivity signal with a preestablished high level and low level value, respectively, and providing an output signal to activate alarm means in the event the value of said conductivity signal is greater or less than said high level and low level values, respectively.