To ensure reliable, efficient operations, it’s crucial that industrial manufacturing companies establish proper procedures and systems for regularly maintaining and calibrating facility equipment. These procedures usually include various types of inspections and tests.
However, many companies struggle with establishing guidelines for pH sensor calibration, and are unsure when and how to perform calibration processes.
pH Sensor Calibration Vs. Calibration Check
When establishing routine practices for calibrating pH, it’s important to first develop your own maintenance and calibration schedule that will work for you and your facility’s operations. The first step in creating this schedule is to actually remove the pH sensor from the equipment after a certain amount of time (e.g., one to two days), so that you can easily examine the sensor to see how frequently it becomes dirty.
If you determine there isn’t any dirt or debris on the sensor, you can then rinse it off and proceed to the next step — a buffer check. This involves immersing the pH sensor into the calibration buffer solution and doing a quick reading of the pH. If the reading falls within the tolerances designated by your facility’s set standards, then you won’t have to worry about calibrating the sensor just yet, and can continue to monitor it. Using this testing process, you can easily determine the average amount of time needed between each cleaning and calibration.
How to Properly Clean a pH Sensor
Of course, having a clean sensor is essential for obtaining accurate pH readings. To guarantee accuracy, it’s important to prevent the glass-measuring electrode from developing any kind of coating. Likewise, it’s also important to prevent any buildup from developing on the reference electrode assembly. If slight coating or scaling does build up on the sensor, it can be easily removed using a water jet from a faucet or spray bottle. For more stubborn coatings, you can also use a gentle acid brush or tooth brush to remove the debris.
Getting the pH fully clean may require immersing the sensor in a hot water solution with common liquid dishwashing soap; this will loosen any debris. Once loosened, you can then scrub the electrode for a few seconds to continue the cleaning process. For really thick or sticky coverings, consider dipping the brush into a 2% hydrochloric acid solution and then carefully scrubbing the electrode. Once you’ve cleaned the sensor, it’s best to rinse it using distilled water; you can then let the sensor soak in tap water or a 7 pH buffer solution for a few minutes to allow the pH sensor to restabilize.
How to Perform a pH Sensor Calibration
If readings are still off once the sensor has been cleaned, you may need to recalibrate the sensor. To perform a pH sensor calibration, it’s necessary to first clear the pH meter, erasing the previous calibration. You should first soak the sensor in a 7-pH buffer solution for a few minutes. If this still doesn’t produce the desired results, then, after rinsing, you should then soak the sensor in a 4-pH buffer solution overnight and rinse, as the second half of a two-point calibration.
Following use of the two solutions, conduct another reading to see if the readings produced fall within your facility’s operational guidelines. If so, you’re all set. But if the readings still don’t meet the set standards — even after cleaning and calibrating the sensor — it may be time to replace the sensor with a new one.
At Endress+Hauser, we realize that pH calibration is a complex process. To make it a little easier, we have developed a comprehensive guide, complete with a step-by-step approach to help users decide when to calibrate, clean, or discard a sensor.
To learn more, download our free eBook today.