Analysis

pH sensors and transmitters

Products for high-quality pH measurement in all industries

More than 30% of all quality-relevant measurements in processes are pH measurements. That’s why reliable pH sensors & transmitters are extremely important for plant optimization and process safety. We offer an extensive portfolio for all conditions, such as stable processes, fast changing media compositions, sticky media, hazardous areas or hygienic applications.

How to select pH electrodes

pH sensors and transmitters are used in many industries such as chemicals, water & wastewater, food & beverage, pharmaceuticals, power plants, primaries and oil & gas. The selection of the sensor depends on the application. Choose the glass sensor’s diaphragm and reference system according to your needs. Use ISFET sensors where glass breakage is intolerable or media contain high amounts of organic solvents. Apply enamel sensors when long-term stability and lowest maintenance are required.

pH measurement with glass electrodes and enamel electrodes

The pH value is used as a unit of measurement for the acidity or alkalinity of a liquid medium. The pH-sensitive element of glass electrodes is a glass bulb that supplies an electrochemical potential which is dependent upon the pH value of the medium. This potential is generated because small H+ ions penetrate through the outer layer of the membrane while the larger negatively charged ions remain in the solution.

Glass pH probes contain an integrated Ag/AgCl reference system that serves as the required reference electrode. The pH value is calculated from the potential difference between the reference system and the measuring system using the Nernst equation. Our pH sensors and transmitters achieve outstanding linear measuring performance over an extremely wide pH range!

The measuring principle of enamel pH electrodes corresponds to that of glass pH sensors, however, the pH-sensitive element is enamel.

pH measurement with ISFET electrodes

The pH value is measured with an ion-selective field effect transistor (ISFET). It is a simple transistor with a source and drain that are separated from the base by a semiconductor. Hydrogen ions from the medium may accumulate here. The resulting positive charge on the outside is ‘mirrored’ on the inside of the base where a negative charge occurs. This makes the semiconductor channel conductive. The more H+ ions accumulate on the base, the more current can flow between the source and drain.

Chlorine sensors and transmitters

Products for reliable measurement of chlorine, total chlorine and chlorine dioxide

Free chlorine, chlorine dioxide or total chlorine (incl. chloramines) are usually measured to monitor and control the disinfection of drinking water, reuse water or pool water. Our sensors are therefore applied in waterworks, cooling towers, bottle cleaning facilities, etc., where they ensure a smooth water treatment compliant to legal limits.

How to select chlorine sensors

Our chlorine sensors and transmitters are used in water & wastewater and in the utilities of many industries such as power or food & beverage. The sensor selection depends on the application: free chlorine sensors are mainly applied in drinking and pool water, whereas chlorine dioxide sensors are often installed in drinking water, food and process water applications. Total chlorine sensors are commonly used in wastewater treatment plants to measure the effluent water’s disinfection status.

Measurement of chlorine, total chlorine and chlorine dioxide

Sensors for chlorine dioxide measurement feature a metallic cathode, which is separated from the medium by a thin membrane. Chlorine dioxide coming from the medium diffuses through this membrane and is reduced at the gold cathode. The circuit is completed by means of the silver anode and the electrolyte. The electron reduction at the cathode is proportional to the concentration of chlorine dioxide in the medium. This process works in a wide pH and temperature range.

Measuring free available chlorine is somewhat different. Here, hypochlorous acid diffuses through the membrane and produces a reaction. The presence of hypochlorous acid in the medium depends on the pH value. This dependency is compensated by means of pH measurement in the flow assembly and balancing in the transmitter. For the measurement of total chlorine, hypochlorous acid and additionally chloramines play a role in a complex system of reactions.

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