Search

EP-4579230-B1 - PH SENSOR MEASUREMENT

EP4579230B1EP 4579230 B1EP4579230 B1EP 4579230B1EP-4579230-B1

Inventors

  • HUANG, JUN
  • CIOBANU, CALIN
  • Worley, Geordon Alexander
  • FORD, JERRY

Dates

Publication Date
20260513
Application Date
20241220

Claims (7)

  1. A method for measuring the impedance of a pH sensor electrode comprising: applying a positive voltage pulse (p1) to the pH electrode: taking a plurality of samples of the electrode voltage response to the positive pulse, the samples being equally timed from each other during application of the positive pulse (p1); from those samples, estimating the impedance of the electrode: and applying a negative voltage pulse (p2) to cancel out induced charges from the positive voltage on the electrode so that the electrode quickly recovers to read media pH levels, the method being characterized in that the negative pulse (p2) is dynamically adjusted as a function of the electrode voltage response.
  2. The method of claim 1 wherein the samples are taken within less than 250 ms of the beginning of the positive pulse (p1).
  3. The method of claim 2 wherein three samples are taken equally spaced apart in time.
  4. The method of claim 3 wherein the three samples are taken before the asymptote of a curve of the electrode voltage response.
  5. The method of claim 1, wherein the width of the negative pulse (p2) is dynamically adjusted.
  6. The method of claim 5 wherein the width of the negative pulse (p2) is dynamically adjusted by: determining the energy of the electrode voltage response after applying the positive pulse (p1); and generating the negative pulse (p2) that substantially matches the total energy of the electrode voltage response.
  7. The method of claim 6, wherein of the pulse width of the negative pulse (p2) is determined by the total energy of the electrode voltage response divided by the voltage amplitude of the positive pulse (p1).

Description

FIELD The present disclosure relates to pH sensors and, more particularly, to techniques for measuring the impedance of a glass pH sensor electrode. BACKGROUND The term pH represents the quantitative measure of the acidity or basicity of aqueous or other liquid solutions. The term, pH = -log[H+], translates the values of the concentration of the hydrogen ion which ordinarily ranges between about 1 and 10-14 gram-equivalents per litre into numbers between 0 and 14. In pure water, which is neutral (neither acidic nor alkaline), the concentration of the hydrogen ion is 10-7 gram-equivalents per litre, which corresponds to a pH of 7. A solution with a pH less than 7 is considered acidic; a solution with a pH greater than 7 is considered basic, or alkaline. A probe capable of measuring pH, consists of two electrodes: a sensor electrode, also known as glass electrode embedded in a special formulation glass and a reference electrode. The ion exchange generates a voltage. Ion exchange occurs on the inner surface of the glass electrode. Since the acidity of the potassium chloride inside the electrode and the solution being measured are different, the activity of the hydrogen ions will be different, resulting in a difference in charge. When this happens, a potential difference occurs between the sides of the glass electrode and the reference electrode, which is proportional with the acidity or alkalinity level of the media solution. For each 1 pH change, the potential also known as Slope changes by 59.16mV. The Reference is kept at an ideal zero potential. The potential difference between the two electrodes is measured and converted into pH level readings. Because the potential difference to be measured is generated across the pH Glass, special measures have to be taken to properly measure the voltage, all due to the high Glass Impedance which ranges from 50 MOhm to 500 MOhm at 25C. When Temperature gets below 25C, the Glass Impedance increases and it decreases when temperature increases. The quality of the pH measurement strongly depends on the condition of the glass. The pH electrodes age which can result in changes to the electrical characteristics of electrode over time or during harsh application or environment. Electrode aging causes an increase of glass/reference impedance, measurement response time, a declining voltage-to-pH slope, especially in the alkaline region, and/or a shift of the asymmetry potential. As an electrode deteriorates, the ability of the probe to accurately measure pH also deteriorates resulting inaccurate and/or inconsistent pH level measurements. The glass electrode impedance increase can be indicative of changes in the chemical composition of the membrane glass, steady growth of the internal membrane gel layer, or mechanically induced damage of the outer gel layer of the membrane during measurement and cleaning. When the Glass breaks, the pH measurement is compromised. For all of the above, being able to measure the glass impedance becomes a good practice for a reliable pH measurement. U.S. Patent No. 9,488,611 to Rezvani et al discloses a method for detecting the impedance of a pH electrode. US 2008/042665 A1 discloses a method of measuring impedance of a pH electrode. A test current is applied to the pH electrode for a time duration that is less than 50 percent of a time constant that is associated with electrical characteristics of the pH electrode. A voltage response of the pH electrode is measured when the test current is applied to the pH electrode. An impedance of the pH electrode is calculated as a function of the voltage response. SUMMARY A method is provided for measuring the impedance of a pH sensor electrode as set out in independent claim 1. The method includes applying a positive voltage pulse to the pH electrode and taking a plurality of equally timed samples of the sensor voltage response and, from those samples, estimating the impedance of the electrode. Then, a negative voltage pulse width is applied to cancel out the induced charges from the positive voltage on the pH sensor so that the sensor quickly recovers to read media pH levels. These and various other features and advantages will be apparent from a reading of the following detailed description using the exemplary embodiment therein described. This summary and the abstract are not intended to identify key features or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS The drawings described herein are for illust