COULOMETRIC SYSTEM HAVING COMPENSATION FOR TEMPERATURE INDUCED VISCOSITY CHANGES

• US 3,621,381 A
• Filed: 10/16/1968
• Issued: 11/16/1971
• Est. Priority Date: 10/16/1968
• Status: Expired due to Term

• Current Assignee: Edgar L. Eckfeldt
• Original Assignee: Edgar L. Eckfeldt
• Inventors: Edgar, L. Eckfeldt
• Primary Examiner(s): Rudolph V. Rolinec
• Assistant Examiner(s): Ernest F. Karlsen
• Application Number:
  US04/797,715
• Time in Patent Office: 1,126 Days
• Field of Search: 324/30,30B,65TC 204/195,1T 73/54,55,59
• US Class Current: 324/441
• CPC Class Codes: G01N 27/423 Coulometry

Abstract

Because of solution flow rate variations occurring as a result of changes in the temperature of the sample solution passed into coulometric measuring cells, continuous coulometric systems of the prior art require use of a metering pump to maintain solution flow rate constant so as to permit accurate solution constituent concentration measurements. The invention permits accurate, continuous concentration measurements to be made coulometrically, independent of any flow rate variations caused by sample solution temperature changes. This is achieved through the use of a device (such as, for example, a thermistor) responsive to the coulometric current, which device develops an output varying with the changes in the concentration of the constituent to be measured and invariant with changes in the flow impedance of the sample solution caused by changes in its temperature.

Claims

1. In a coulometric system having current electrodes for flow of current through a stream of solution flowing at a substantially constant rate at any given temperature in determination of the concentration of a constituent of the solution, the improvement comprising:

means responsive to said current for developing an output varying with changes in the concentration of said constituent and invarient with changes in the flow rate of said solution due solely to changes in its temperature, said means responsive to said current comprising variable resistance means connected in circuit with said electrodes for developing an output voltage representative of the concentration of said constituent in said solution, and means external to said circuit responsive to changes in the temperature of said solution for varying the resistance of said variable resistance means with changes in the flow rate of said solution due solely to changes in its temperature to maintain said output voltage representative of the concentration of said constituent.

2. A coulometric system for measuring the concentration of a constituent of a solution, including:

a coulometric cell having current electrodes disposed for flow of current therebetween, flow control means having a definite and predetermined temperature-flow rate characteristic for control of delivery of solution to said cell for maintaining the flow of solution to said cell constant at any given temperature, means for passing through said electrodes a coulometric current of magnitude proportional to said constituent, means for producing a measurable voltage produced by said current, and temperature responsive means having a temperature characteristic related to said temperature-flow rate characteristic of said flow Control means to continuously alter said measurable voltage in a manner to render it invariant with changes in the flow rate of solution in said cell due to change of the temperature of said solution.

3. The coulometric system of claim 2 wherein, said flow control means includes means for delivering said solution to said cell at a constant pressure, and said cell includes a solution flow channel for maintaining the flow of said solution through said cell constant at any given temperature.

4. The coulometric system of claim 2 in which said flow control means comprises a flow impedance device.

5. The coulometric system of claim 4 in which the flow impedance device comprises a capillary tube.

6. A coulometric system for measuring the concentration of a constituent of a stream of solution, comprising:

flow control means having a definite and predetermined temperature-flow rate characteristic for regulating the rate of flow of said stream of solution, means including electrodes for causing an electric current to flow through said stream of solution, means responsive to said flow of electrical current through said stream for developing an output signal that is proportionally related to the concentration of said constituent in said solution, and temperature responsive means disposed to respond to the temperature of the solution of said stream, said temperature responsive means having a temperature characteristic related to said temperature-flow rate characteristic of said flow control means to effect a modification of said output signal in a manner to render said output signal invariant with changes in the flow rate of said stream of solution due solely to changes in solution temperature.

7. The coulometric system of claim 6 in which the means responsive to said electrical current includes a temperature-responsive means having an impedance element in heat exchange relation with said solution of said stream.

8. The coulometric system of claim 6 in which said means responsive to said flow of electrical current comprises a variable resistance means connected in circuit with said electrodes for developing an output voltage representative of the concentration of said constituent in said solution, and said temperature responsive means comprises a means external to said circuit responsive to changes in the temperature of said solution for varying the resistance of said variable resistance means with changes in the flow rate of said solution due solely to changes in its temperature to maintain said output voltage representative of the concentration of said constituent.

9. The coulometric system of claim 6 in which the temperature responsive means includes a resistance element providing a thermal coefficient of resistance substantially matching the thermal coefficient of viscosity of said solution and is maintained at the temperature of said solution for developing an output voltage representative of the concentration of said constituent and of a value independent of changes in the viscosity of said solution due to changes in its temperature.