pH measurement in industry & process
Pressure, heat, aggressive chemistry: when the measuring point is part of the plant, different rules apply - from the fitting to the digital sensor.
From meter to measuring point
In the process industries, the pH electrode is not a hand-held device but a permanently installed part of the plant: it controls neutralisations in chemicals, monitors electroplating baths, regulates bioreactors and safeguards product quality in paper and textiles. Failure or mismeasurement here does not mean wrong numbers but production disruption - the demands on reliability and serviceability are correspondingly high.
Pressure and temperature
Process electrodes are specified for conditions where laboratory electrodes fail: operating pressures of several bar and temperatures up to 130 °C (for example for sterilisation-in-place in biotechnology). Important to know: high temperatures considerably accelerate the ageing of any glass membrane - an electrode measuring continuously at 80 °C lives much shorter than its datasheet maximum suggests. Pressurised or polymer reference systems prevent process medium being pushed into the electrode.
Fittings and retractable assemblies
- Immersion fittings hang the electrode from above into basins and vessels.
- Flow-through fittings route a partial stream of the line past the membrane in a defined way.
- Retractable assemblies are the top class: they move the electrode in and out while the process runs - for cleaning, calibration or replacement without a plant stop. The widespread mechanical standard is the PG13.5 thread with a 12 mm shaft.
Analogue or digital?
Classic electrodes deliver their high-impedance millivolt signal analogue to a transmitter - proven, but sensitive to moisture in the connector and long cable runs. Digital sensors convert the signal directly in the electrode head and store their own calibration data: the electrode is calibrated in the lab and merely plugged in at the measuring point. In new plants this concept is steadily gaining ground.
Aggressive media
Strongly alkaline liquors call for low-alkaline-error special glasses, hot acids for temperature-resistant membranes - and media containing hydrofluoric acid rule out glass entirely (antimony or ISFET sensors step in here). For process applications, the choice of membrane glass, junction and shaft material should always be matched to the specific medium.
Matching products: Process electrodes and accessories for industrial applications are available in our shop aquaundco.com (German-language).