Electricity: measuring and testing – Electrolyte properties – Using a conductivity determining device
Reexamination Certificate
2002-03-01
2003-12-16
Chapman, John E. (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
Using a conductivity determining device
C324S444000
Reexamination Certificate
active
06664793
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for measuring the presence and various qualities of fluids, and materials containing fluids. More specifically, the present invention describes a process for detecting minute compositional changes in single sampling or continuous flow monitoring of fluids which offers extreme sensitivity, simplified temperature compensation, probe design, materials and control electronics.
BACKGROUND OF THE INVENTION
A myriad of fluids are used in many scientific and industrial processes, as well as in end user applications. Initial, in-process and in-use testing of these fluids can often help prevent potential problems. Many processes rely on precise mixtures of fluids, slurries, suspensions or wetted materials and require accurate feedback on the resultant mixtures. End users often depend on accurate compositions of fluids, slurries, suspensions or wetted materials for safe and efficient use. Qualitative measurement of these materials can often prevent costly mistakes, damage or injury.
Electronic analysis of fluid compositions has historically been complicated by the fact that generally any such fluid has a dielectric constant, conductance and double-layer effects, each of which produces complex electrical responses. While measurements of these qualities are commonplace, they are plagued with instrumental difficulties such as probe design, erratic temperature dependencies and complex control electronics in the effort to get accurate and sensitive results.
In-use or in-process controls often require sensors capable of properly handling varying levels of flow, pressure and temperature while accurately measuring compositional changes. Current methods of measuring the dielectric constant or conductance of a fluid require either a very small range of variance in any of these effects, or extreme and technically complex compensations for them.
The dielectric constant of fluids is a common qualitative measure associated with fluids. It is known that the dielectric constant in solids is a measure of the ability of molecules to polarize or shift their internal charges in response to external fields. In fluids, the molecules Are also able to move about, rotating to orient in a field and/or migrating within the fluid. In electronic terms, the dielectric constant is the analog of a capacitor.
Many patents exist that are directed to measuring the capacitance of fluids. U.S. Pat. Nos. 4,132,944, 5,497,753 and 5,507,178 are representative of capacitance-measuring techniques.
Conductivity (the reciprocal of electrical resistance) is another common measure used to produce a qualitative indication of fluid compositions and charged species in a fluid. Charged species, or ions, present in a fluid provide a means for the passage of electrons through a fluid. The more ions present, the lower the electrical resistance of the fluid and the greater the magnitude of current that can flow through the fluid. In electronic terms this phenomenon is the analog of a resistance.
Numerous patents have been directed to fluid conductivity measurements, including U.S. Pat. Nos. 4,132,944, 4,634,982, 6,169,394 and 6,232,783, all representative of conductivity based applications.
Both of the above-described measures are greatly affected by temperature and other influences. In many cases, the precise theory behind these wide variances is not directly known or reliably predicted and varies considerably dependent on composition.
Measurements of conductivity and dielectric properties together have been performed in the past in efforts to simplify and solve many of the problems highlighted above. U.S. Pat. Nos. 4,516,077 and 6,169,394 are representative of this approach. In the latter patent, complex measurements were made of the electrical impedance of a fluid (i.e., the effect of a parallel resistance and capacitance). Unfortunately, this invention used complex electronics in generating a wide range of excitation frequencies, while-variances such as temperature dependencies were not addressed.
In U.S. Pat. No. 4,516,077, a sensor is described which is useful in a limited number of solvent solutions including water, alcohols and glycols. This invention included a method of electronically charging a fluid, disconnecting the charging means, and then measuring the time necessary for the charge across the fluid to dissipate (termed the “intrinsic time constant”). This invention essentially measures the re-diffusion rate of the polarization and electrical charges as they return to equilibrium devoid of any external electrical influences and is greatly affected by temperature and fluid flow rates.
The measurement of any fluid quality is complicated by the electrode-fluid interface. Each such interface includes its own resistance and capacitance, which are known to often be larger than those of the fluid itself. Electrochemical reactions caused by the introduction of an electrical current into a fluid can cause electrode corrosion and contamination. Sensed voltages or currents often need amplification and signal conditioning to provide suitable readings. These, and other problems, have seldom been addressed in previous inventions.
Therefore, it is desirable to develop an invention that uses the electrical qualities of the fluid to provide the primary measure while avoiding the above-described complications.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a process for measuring the presence and various qualities of fluids and materials containing fluids. It offers improved performance over previous methods in its range and sensitivity, as well as relative insensitivity to temperature and fluid flow. In addition, this process offers simplified design and measurement.
The present invention includes a process and an apparatus for controlling and measuring various electrochemical effects of simplified electrochemical cells. However, the underlying effects measured are complex in nature. The present invention controls some of the individual influences of those effects to derive a measurement that has advantages over previous techniques and is termed here Transient Immitivity Response (TIR).
The primary feature of the invention is the use of a capacitance external to the cell to accumulate, control and limit the electrical currents passing through the cell. Transient immitivity response refers to the interactions between this capacitance and the current transfer mechanisms within the electrochemical cell. These interactions create a complex rate of electrical charging and discharging of this external capacitance that can be measured in many different ways. This capacitance, the cell configuration and other external components may be adjusted to enhance or reduce the effect of various charge transfer mechanisms and to fit the invention to virtually any fluid. The transient immitivity response is the time related complex rate at which charge is passed through the cell and accumulated on the external capacitance.
One embodiment according to the invention includes two electrodes spaced apart from each other and both in contact with a fluid-being tested. This embodiment includes an excitation source for providing a time-varying excitation voltage to a first one of the electrodes. The excitation voltage is switched between a first defined voltage level and a distinct second defined voltage level. The first and second voltage levels are alternatively applied to the first electrode for specific time periods. This source has a low source resistance such that it is able to supply sufficient electrical current to change the first electrode's electrical potential in a minimal time and thereby rapidly charge the first electrode's capacitance.
According to the invention, a defined capacitance is located between the second electrode and an electrical or circuit ground. The ground has a defined voltage. This embodiment also includes a voltage detector for detecting a sensed voltage induced on the defined capacitance. The sensed voltage is proportional to electrical charg
Davis Robert E.
Sampson Allen R.
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