Corrosion measurement system

• US 5,854,557 A
• Filed: 12/10/1996
• Issued: 12/29/1998
• Est. Priority Date: 04/16/1993
• Status: Expired due to Term

• Current Assignee: Rohrback Cosasco Systems, Inc. (Halma PLC)
• Original Assignee: Eugen Tiefnig
• Inventors: Tiefnig, Eugen
• Primary Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US08/763,974
• Time in Patent Office: 749 Days
• Field of Search: 324/700, 324/71.1, 324/71.2, 204/404, 205/775.5, 205/777, 422/53
• US Class Current: 324/700
• CPC Class Codes: G01N 17/00 Investigating resistance of materials to the weather, to corrosion, or to light

Abstract

An improved corrosion measurement system for determining the rate of corrosion of a fluid medium. The system is comprised of a highly sensitive excitation and amplification electronic circuitry for registering and displaying the stable and accurate measurement results. A unique unitized measurement probe is temperature stabilized using thermally inertially balanced metallic probes; the first reference element being coated with an impermeable insulating coating, the second, the corroding element, being fully exposed to the corrosive fluid medium.

Claims

1. A corrosion measurement system for use in a particular corrosive medium to obtain measurements for determining a rate of corrosivity of the medium, comprising:

a probe having a reference element and a corroding element, each element having identical physical properties, the probe adapted for contacting the corrosive medium, the reference element having a conformal coating that protects the reference element from exposure to corrosivity of the medium, and the corroding element fully exposed for corrosion by the medium;

a measuring circuitry with a power source associated with the elements of the probe for measuring a rate of corrosivity; and

,

means for instantaneously displaying the rate of corrosivity of the medium, said means in communication with the probe.

2. A corrosion measurement system as described in claim 1, the measuring circuitry power source further comprising an oscillator communicating with the probe for providing an excitation voltage that essentially generates a low distortion sinusoidal waveform through the probe to the measuring circuitry.

3. A corrosion measurement system according to claim 2, wherein the oscillator comprises a Wein bridge oscillator that oscillates within a frequency range from 700 to 900 Hertz.

4. A corrosion measurement system according to claim 3, the measuring circuitry further comprising a step down transformer with a primary winding and a secondary winding, the primary winding driven by the low distortion sinusoidal waveform from the oscillator.

5. A corrosion measurement system according to claim 4, the reference element further comprising a serial resistor and the corroding element further comprising a serial resistor and the secondary winding communicating with the reference element through its serial resistor and with the corroding element through its serial resistor.

6. A corrosion measurement system according to claim 5, the reference element having a reference resistance and the corroding element having a corroding element resistance, the reference element and its associated measuring circuitry comprising a reference channel, and the corroding element and its associated measuring circuitry comprising a corroding channel, each channel having a differential amplifier that amplifies a voltage drop across its respective element resistance, succeeded by a buffer amplifier and full-wave rectifiers and filters connected to a microprocessor having an analog-to-digital converter input respective to each of the channels, whereby changes of resistance of the reference and corroding elements are measured by the microprocessor.

7. A corrosion measurement system as described in claim 6, further comprising a means for compensation for variations in temperature of the measuring circuitry associated with the reference channel and with the corroding channel.

8. A corrosion measurement system as described in claim 7, wherein the means for displaying comprises a display unit associated with the microprocessor for real time read out of the rate of corrosivity of the medium.

9. A probe for use in a corrosion measurement system operative on a particular corrosive medium to obtain measurements for determining a rate of corrosivity of the medium, the probe comprising:

a probe body with a distal end, a reference element and a corroding element, each element having a terminal end;

a probe circuitry with a power source to register a resistivity of the reference element and resistivity changes of the corroding element; and

,

measuring circuitry associated with the probe elements of the probe body for measuring the rate of corrosivity; and

,

a means for compensating for thermal and current variations for precision in measuring the rate of corrosivity.

10. A probe according to claim 9 above, wherein the reference element and the corroding element are each constructed of a metallic material that is the same for each element.

11. A probe according to claim 10, wherein the reference element and the corroding element each have a mass which is the same for each element to thermally compensate measurements for determining a rate of corrosivity.

12. A probe according to claim 10, wherein the reference element and the corroding element each have a physical geometry that is the same for each element.

13. A probe according to claim 12, the reference element further comprising an outer surface having a coating of a material that is impermeable to the corrosive medium for protecting the reference element from the corrosive medium.

14. A probe according to claim 9 above, the measuring circuitry further comprising a reference channel connected to the reference element through a series resistor and a corroding channel connected to the corroding element through a series resistor, each channel further having a reference resistance, followed by a differential amplifier, a buffer amplifier, and a full-wave rectifier-and-filter, that communicate with an ADC converter for each channel for input to a microprocessor, to determine an initial offset prior to each corrosivity measurement.

15. A probe according to claim 14, the means for compensating comprising each element having essentially identical physical properties, including shape, mass and material composition, to achieve a thermal inertia for reducing thermal gradients;

and, a measured corrosivity reduced by the initial offset to further eliminate temperature and current variations.

16. A probe for use in a corrosion measurement system operative on a particular corrosive medium to obtain measurements for determining a rate of corrosivity of the medium, the probe comprising:

a probe body with a distal end, a reference element and a corroding element, each element constructed of the same metallic material, having an identical mass and shape, and each having a terminal end;

the reference element further comprising an outer surface having a coating of a material that is impermeable to the corrosive medium for protecting the reference element from the corrosive medium;

a probe circuitry with a power source to measure a resistivity of the reference element and resistivity changes of the corroding element; and

,

measuring circuitry associated with the probe elements of the probe bodyfor measuring a rate of corrosivity measurement results.

17. A probe according to claim 16, wherein the coating material of the reference element is characterized by a high degree of thermal conductivity.

18. A corrosion measurement system according to claim 17, wherein the coating material of the reference element is characterized by a high degree of electrical insulation.

19. A corrosion measurement system according to claim 18, wherein the terminal end of each of the elements is flush with the probe body distal end, whereby the probe is adapted for total immersion in a corrosive medium.

20. A corrosion measurement system according to claim 18, wherein the terminal end of each of the elements projects outward from the probe body, whereby the probe is adapted for measurement of a rate of corrosivity of a medium by immersing the elements only in a corrosive medium.

21. A corrosion measurement system as described in claim 20, wherein the reference element and the corroding element are thermally insulated from the probe body.

22. A corrosion measurement system for use with a particular corrosive medium to obtain measurements for a rate of corrosivity of the medium, comprising:

a probe having a covered reference element and an exposed corroding element;

a measuring circuitry associated with the elements of the probe for measuring rate of corrosivity, the circuitry having a zero frequency constant current DC source from one to five amperes; and

,

means for displaying the rate of corrosivity of the medium in communication with the probe.

23. A system to determine the corrosivity of a fluid medium by the changes in a corroding mass of a metallic material respective to a reference mass, while both masses are in contact with the fluid medium, the system comprising:

a probe having a reference element and a corroding element, each element comprising the same material and having the same shape and mass, contacting the fluid medium;

means for protecting the reference element from corrosion by the fluid medium surrounding the reference element;

means for supplying the system with an electrical current, for providing an essentially constant reference resistance and a fluctuating corrosion resistance that increases as the mass of the corroding element is diminished by corrosivity;

means for ratiometric measurements of the reference and corrosion resistances associated with the probe, that essentially eliminates influences external to the system;

means for real-time determination of the rate of corrosivity of the fluid medium by measuring and comparing resistance changes of the elements, that are primarily caused by loss of mass of the corroding element; and

,

means for displaying the rate of corrosivity of the medium in communication with the probe.

24. A corrosion measurement system for use in a particular corrosive medium to obtain measurements for determining a rate of corrosivity of the medium, comprising:

a probe having a reference element and a corroding element, each element having identical physical properties and each element adapted for contacting the corrosive medium;

a measuring circuitry with a power source associated with the elements of the probe for measuring a rate of corrosivity;

the measuring circuitry power source further comprising a Wein bridge oscillator that oscillates within a frequency range from 700 to 900 Hertz, the oscillator communicating with the probe for providing an excitation voltage that essentially generates a low distortion sinusoidal waveform through the probe to the measuring circuitry, and a step down transformer with a primary winding and a secondary winding, the primary winding driven by the low distortion sinusoidal waveform from the oscillator.

means for displaying the rate of corrosivity of the medium in communication with the probe.

25. A corrosion measurement system according to claim 24, the reference element further comprising a serial resistor and the corroding element further comprising a serial resistor and the secondary winding communicating with the reference element through its serial resistor and with the corroding element through its serial resistor.

26. A corrosion measurement system according to claim 25, the reference element having a reference resistance and the corroding element having a corroding element resistance, the reference element and its associated measuring circuitry comprising a reference channel, and the corroding element and its associated measuring circuitry comprising a corroding channel, each channel having a differential amplifier that amplifies a voltage drop across its respective element resistance, succeeded by a buffer amplifier and full-wave rectifiers and filters connected to a microprocessor having an analog-to-digital converter input respective to each of the channels, whereby changes of resistance of the reference and corroding elements are measured by the microprocessor.

27. A corrosion measurement system as described in claim 26, further comprising a means for compensation for variations in temperature of the measuring circuitry associated with the reference channel and with the corroding channel.

28. A corrosion measurement system as described in claim 27, wherein the means for displaying comprises a display unit associated with the microprocessor for real time read out of the rate of corrosivity of the medium.