Using a single pH sensor type is not feasible for all applications. Different sensor types are often necessary for laboratory and process measurements due to the wide range of pH applications. Electrode manufacturers aim to address these diverse needs by offering various sensor designs. Some examples are outlined below.
Process pH Sensor
This electrode shape is the most common and can serve various applications in laboratory and process control. Manufacturers produce measuring, reference, and combination electrodes with this construction.
The common design has a 12 mm diameter and employs a PG13.5 mounting thread for installation.
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Adjustable Diaphragm pH Sensor
This standard combination sensor with a ground sleeve liquid junction is mainly used in laboratory settings for measuring dirty or heavily contaminated solutions. It can also work with non-aqueous media.
The junction can be easily cleaned by pushing the sleeve upward. KCl electrolyte can be added through a filling port under the grey cover on the sensor body. Limited use exists in process control due to potential vibration issues.
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Adjustable Diaphragm with Refillable Reference
This design includes two key features: a ground sleeve junction and a side-arm filling tube. To reduce maintenance and pressurize the reference electrolyte, an external electrolyte reservoir connects to the electrode through the filling tube.
This electrode design is suitable for laboratory and process control applications, particularly for controlling high-purity water in boilers and power plants.
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Externally Pressurized pH Sensor
Primarily employed in the chemical industry and biotechnological processes, this refillable electrode design features a large electrolyte vessel, sometimes combined with an intermediate electrolyte vessel.
The entire sensor can be externally pressurized and sterilized with hot steam, requiring a special electrode holder. It is not recommended for laboratory use due to excess hardware.
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Reduced Diameter pH Sensor
Used in laboratory scenarios where small samples need measurement, this electrode design is common in test tubes, NMR tubes, microtiter plates, and other applications where a standard 12 mm pH sensor will not fit appropriately. Hamilton offers specialized laboratory sensors for reference.
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Flat Membrane Glass pH Sensor
A notable feature of this laboratory sensor design is its flat glass membrane, allowing operators to measure pH on surfaces like skin, leather, and paper. Hamilton provides this electrode with an unbreakable plastic shaft, as it is often used with portable pH meters, aptly named the "FlaTrode."
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Plastic Body pH Sensor
Exclusively used in combination electrodes with a gel or polymer reference electrolyte, this sensor design boasts a completely plastic shaft, ensuring it remains unbreakable. This feature is highly desirable when paired with a portable pH meter.
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Food and Dairy pH Sensor
Utilizing a pointed electrode, this design is typically employed in food and dairy industry measurements. The spear-shaped electrodes are well-suited for use with meats and cheeses, and Hamilton offers several laboratory pH sensors for food industry applications.
Image Credit: Hamilton Process Analytics
This information has been sourced, reviewed and adapted from materials provided by Hamilton Process Analytics.
For more information on this source, please visit Hamilton Process Analytics.