Corrosivity measuring device with temperature compensation

• US 6,919,729 B2
• Filed: 01/06/2003
• Issued: 07/19/2005
• Est. Priority Date: 01/06/2003
• Status: Expired due to Fees

• Current Assignee: Rohrback Cosasco Systems, Inc. (Halma PLC)
• Original Assignee: Rohrback Cosasco Systems, Inc. (Halma PLC)
• Inventors: Tiefnig, Eugen
• Primary Examiner(s): Deb, Anjan
• Assistant Examiner(s): Dole, Timothy J.
• Application Number:
  US10/336,885
• Publication Number:
  US 20040130340A1
• Time in Patent Office: 925 Days
• Field of Search: 324/71.1, 324/691, 324/700, 324/721
• 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 novel current feedback amplifier maintains a constant alternating current voltage across the reference element, by simultaneously controlling the current through the serially connected reference and corroding elements, thereby keeping the corrosivity measurement independent of the probe'"'"'s ambient temperature. The unique unitized electrical resistance measurement probe is also temperature stabilized using thermally bridged and balanced metallic elements; the first reference element being coated with an impermeable insulating coating, the second, the sacrificial corroding element, being fully exposed to the corrosive fluid medium.

Claims

1. A corrosion measurement system for simultaneously determining the corrosivity and rate of corrosion of a particular fluid medium in real-time, comprising:

a temperature compensated measurement circuit with a probe contacting the fluid medium, having a pair of substantially identical electrodes comprising a reference element and a corrosivity element, wherein each element is identical in mass, metallic composition and physical geometry;

the circuit having input signals from each element, further comprising a means for maintaining a constant voltage across the reference element;

a means for conditioning a primary reference element signal;

a means for conditioning a corrosivity element measuring circuit signal;

each of said means for conditioning having outputs to an ADC converter and to a microprocessor.

2. The corrosion measurement system according to claim 1, further comprising feedback control loop including a current regulator feedback circuit with a feedback regulator with an input signal derived from the probe reference element, thereby compensating for any temperature variation.

3. The corrosion measurement system according to claim 2, further comprising a forward path reference measurement channel and a forward path corrosion measurement channel.

4. The corrosion measurement system according to claim 3, the forward path reference measurement channel comprising a differential reference amplifier, a high pass filter, and an RMS-to-DC converter.

5. The corrosion measurement system according to claim 4, the forward path corrosivity measurement channel comprising a differential reference amplifier, a high pass filter, and an RMS-to-DC converter.

6. The corrosion measurement system according to claim 3, further comprising a temperature reference element communicating on a temperature reference channel of the circuit.

7. The corrosion measurement system according to claim 6, the temperature reference element having a voltage input to a differential amplifier, a high pass filter to remove all DC voltage components, and to RMS-to-DC converter having a low pass filter connected to its output, where an output channel connects to the negative input of the analog-to-digital converter and to the microprocessor.

8. The corrosion measurement system according to claim 6, further comprising a multiplexed switching arrangement including four independent switches for automatic activation of the respective channels of the system.

9. The corrosion measurement system according to claim 8, wherein a difference between the reference element signal and the corrosivity element signal is provided both at zero and at full scale, for self-calibration of the system.

10. The corrosion measurement system according to claim 9, the reference element comprising a fluid medium temperature determining element.

11. The corrosion measurement system according to claim 10, wherein the reference element and the corrosion element are connected in series.

12. The corrosion measurement system according to claim 11, the temperature reference connected in series with the reference element and the corroding element.

13. The corrosion measurement system according to claim 12, the current regulator feedback circuit comprising a forward path channel and a feedback channel.

14. The corrosion measurement system according to claim 13, the current regulator forward path channel comprising a differential reference amplifier, a high pass filter and an RMS converter.

15. The corrosion measurement system according to claim 14, the feedback path channel comprising an amplitude control sinusoidal oscillator and voltage to current converter.

16. The corrosion measurement system according to claim 13, further comprising a thermal bridge connecting the reference element and the corrosion element, whereby said elements are thermally connected to maintain a constant temperature between the reference and the corroding element to eliminate errors caused by thermal gradients.

17. The corrosion measurement system according to claim 13, wherein a temperature gradient between the reference element and the corroding element is essentially zero.

18. The corrosion measurement system according to claim 17, each element having a thermal inertia of its mass essentially equal to the other;

and, a ratio of voltages across each element is thermally compensating, thereby eliminating errors due to a thermal tracking due to an equality of thermal inertia of the two masses.

19. The corrosion measurement system according to claim 18, wherein the reference element is coated with an impermeable material to prevent a corrosive medium from corroding it.

20. The corrosion measurement system according to claim 19, wherein the protective material coating of the reference element comprises thermal conduction and thermal transfer properties.

21. The corrosion measurement system according to claim 20, wherein the coating further comprises electrical insulating properties.