You need to maintain in-line pH sensors for ensuring high-performance measurements and extending the lifespan of your equipment.
In this guide, we outline the fundamentals of regular inspection, proper storage, and effective chemical cleaning techniques tailored to specific contaminants. We also explore how transitioning to digital sensors with Intelligent Sensor Management (ISM™) can simplify your workflow through predictive diagnostics and off-line calibration
Most in-line pH sensors have a glass membrane that senses pH plus a reference electrode, both built into a single body. Because they are exposed to process fluids, the surface of the sensors can get dirty from deposits, coatings, or chemicals that can affect how well they operate. In addition, glass pH sensors are fragile and can be damaged during handling or in the process. Checking them regularly can catch potential problems early.
Inspect the sensor often for any damage, cracks, or buildup on its surface. Make sure the reference junction is not blocked and is in good condition.
Calibrate the sensor regularly using standard buffer solutions to keep it accurate. How often you calibrate depends on your application, process conditions, and the sensor type. Always use fresh buffers and follow the manufacturer’s instructions.
When you are not using the pH sensor, store it in the right storage solution to keep the glass membrane from drying out. Never store sensors in deionized or distilled water as this can remove ions from the glass and harm performance.
Sensors wear out over time and need to be replaced. If you notice slow response, frequent calibration problems, or unstable readings, it may be time for a new sensor. Follow the manufacturer’s advice or replace based on performance.
It’s important to clean a sensor if its surface gets dirty or fouled, since this can cause incorrect readings.
To remove general deposits, rinse the sensor with distilled water to wash away loose particles. Do not use abrasive materials, as they can scratch the pH-sensitive glass membrane.
Use a cleaning solution that’s appropriate for what’s causing the fouling:
- Protein or organic fouling: Soak the sensor in a mild detergent or enzymatic cleaner. Soak the sensor for a short time, then rinse it well.
- Inorganic deposits (scaling): Use a weak acid solution, such as 0.1 M hydrochloric or citric acid, for a short time to remove mineral deposits. Avoid strong acids or soaking for too long, as this can damage the sensor.
- Oil or grease contamination: Soak the sensor for a short time in alcohol or acetone, then rinse it well with distilled water. Scratching the glass membrane or reference junction can permanently damage the sensor. Use soft brushes or cloths if manual cleaning is necessary.
After cleaning, you may need to soak the sensor in a storage solution or pH 4 buffer to help it work properly again.
METTLER TOLEDO digital pH sensors with Intelligent Sensor Management (ISM™) technology simplify sensor maintenance. ISM features an Adaptive Calibration Timer that predicts when calibration will be required. And with ISM Core PC software, you can:
The pH Theory Guide combines theory and practice in one comprehensive resource, covering everything from basic principles to advanced topics like sensor performance, calibration strategies, and measurement reliability in demanding applications.
Find out more about pH sensors in our pH Theory Guide!
pH is measured in manufacturing and production processes for a wide variety of reasons, such as those explained here.
To calibrate an in-line pH sensor effectively, follow the steps described here to attain accurate, reliable pH measurements.
