Glossary · Sensors and measurement
pH sensor
Also known as: pH electrode, pH probe
German: pH-Sensor
In process analytics, a pH sensor is a sensor that measures the acidity or alkalinity of an aqueous solution, usually with a glass electrode and a reference electrode whose potential difference depends on the hydrogen ion activity.
- Sensors
- Process industry
In one sentence
A pH sensor measures how acidic or alkaline a liquid is, usually with a glass and reference electrode, and needs regular calibration.
Example
A pH sensor in a neutralization tank controls the dosing pumps for acid and caustic so that the wastewater leaves the plant within limits.
How it applies
- Engineering: Electrode type, diaphragm and material must suit medium, temperature, pressure and cleaning. Temperature compensation corrects the electrode slope; the pH of the medium itself also changes with temperature.
- Commissioning: Calibrate with at least two buffer solutions and record zero point and slope.
- Maintenance: pH electrodes age and drift. Regular cleaning, calibration and replacement are part of normal operation, and slope and zero point indicate the electrode condition.
- Documentation: Give calibration intervals, buffer values, storage conditions and handling warnings, since glass electrodes break and buffer or cleaning solutions can be hazardous. Digital sensors that store calibration data in the sensor head change the procedure, so describe the actual one.
pH sensor vs. conductivity sensor
A pH sensor measures hydrogen ion activity. A Conductivity sensor measures the total ionic conductivity and cannot tell acid from salt.