It is not possible to use one pH sensor type for every application. More often in laboratory and in process measurements different sensor types are required as there are numerous pH applications. Electrode manufacturers try to cover most of these applications by offering varying sensor designs. Some examples are provided below:
Process pH Sensor
This is the most common electrode shape and a wide field of applications can be covered with this type of electrode, both in the laboratory and in process control. Measuring, reference and combination electrodes are manufactured using this construction. The combination electrode is the common 12mm diameter sensor design and uses a PG13.5 mounting thread for installation.
Adjustable Diaphragm pH Sensor
A standard combination sensor construction with a ground sleeve liquid junction. This electrode is mainly used in the laboratory where dirty or strongly contaminated solutions have to be measured. Its application includes non-aqueous media as well. The junction can easily be cleaned by pushing the sleeve upwards. Liquid KCl electrolyte can be added to the sensor through a filling port underneath the grey cover on the sensor body. There is a limited use for this construction in process control (be aware of vibration). See the FlushTrode for more information.
Adjustable Diaphragm with Refillable Reference
This design example includes two electrode features: a ground sleeve junction and a side-arm filling tube. In order to minimise maintenance time and to pressurise the reference electrolyte an external electrolyte reservoir is connected to the electrode via the filling tube. This electrode design can be used in the laboratory and in process control, especially for high purity water control found in boilers and power plant applications. See the IonoTrode for more information.
Externally Pressurized pH Sensor
This refillable electrode design is mainly used in the chemical industry and in biotechnological processes. The reference electrode features a large electrolyte vessel which is sometimes combined with an intermediate electrolyte vessel. The entire sensor can be externally pressurized and also sterilized with hot steam. A special electrode holder is required for this electrode. Due to the excess hardware this sensor is not suitable for laboratory applications. See the ChemoTrode for additional options.
Reduced Diameter pH Sensor
The below electrode design is used in the laboratory where small samples have to be measured. It is commonly used in test tubes, NMR tubes, microtiter plates, and other applications where a conventional 12mm pH sensor will not properly fit. See Hamilton’s special use laboratory sensors for reference.
Flat Membrane Glass pH Sensor
The main feature of this laboratory sensor design is the flat glass membrane which enables the operator to measure the pH of surfaces, such as skin, leather, paper, etc. Hamilton supplies this electrode with an unbreakable plastic shaft, as it will often be carried around and used with a portable pH meter. This sensor is appropriately named the FlaTrode.
Plastic Body pH Sensor
This sensor design is used exclusively for combination electrodes featuring a gel or polymer reference electrolyte. The shaft is made completely from plastic. This design makes the shaft unbreakable which is highly desirable in applications where it is paired with a portable pH meter.
Food and Dairy pH Sensor
The below design uses a pointed electrode. It is normally applied in the food and dairy industry measurements. The spear-shaped electrodes are ideal for use with meats and cheeses. Hamilton offers several laboratory pH sensors used in the food industry.