Greg McMillan presented pH Measurement Best Practices at the recent Mary Kay O’Connor Safety & Risk Conference as part of the 79th Annual Instrumentation and Automation Symposium For the Process Industries. Here is the abstract from the pH Measurement Best Practices paper that Greg also submitted.
pH measurement has the greatest sensitivity and rangeability by far of any ion composition measurement. However, there are many challenges in terms of the installed accuracy and life expectancy. Many electrode designs have severe limitations when used in an industrial plant that could dramatically increase errors and failure rate. Here we provide guidance on the effect of process conditions and electrode designs, and offer best practices to take advantages of the advances in electrode technology, calibration, installation designs, and online diagnostics to get the best performance and reliability.
Many of the best practices Greg shared come from his book Advanced pH Measurement and Control, Fourth Edition. It provides the insights and guidance needed for electrode selection, installation, calibration, troubleshooting, and the advantages of middle signal selection.
He described the operation of Double Junction Combination pH Electrodes. High acid or base concentrations can affect the glass gel layer and reference junction potential. An increase in noise or decrease in span or efficiency indicates a glass electrode problem, which can cause a shift or drift in pH measurement.
The life of an electrode depends on the operating conditions. High acid or base concentrations at the extremes of the titration curve decrease the electrode’s life for a given operating temperature. A reduced life can lead to measurement accuracy and response time deterioration. Control strategies such as pH feedforward control become unreliable due to inaccurate feedforward effects and timing. As glass electrodes age, their response slows. Higher temperatures cause premature aging in these electrodes.
Greg showed some horizontal and vertical piping arrangements. Here is the horizontal piping arrangement.
Here is the vertical piping arrangement.
Wireless pH transmitters eliminate problems caused by electrical ground noise spikes in wired transmitters. He also recommended using a middle signal selection control strategy, which:
Greg offers a bulleted list of best practices in the final ten slides of the presentation. Make sure to follow the presentation link to read these. The paper provides additional details about these best practices. Visit the Liquid Analysis Sensors section on Emerson.com to learn more about Rosemount pH/ORP sensors and other analytical probes.
The post Greg McMillan’s pH Measurement Best Practices appeared first on the Emerson Automation Experts blog.