What is pH?
The pH value is often used for water measurements and is a measure of the acidity and alkalinity, or the corrosive and alkaline action of a particular solution. The pH value is generally expressed as a numerical value from 0 to 14. The value 7 stands for neutrality. Water with a pH value of 7 is therefore neither acidic nor basic. The numbers on the scale increase with increasing alkalinity (basic), while the numbers on the scale decrease with increasing acidity (acid). Each unit of change represents a tenfold change in acidity or alkalinity. The pH value is also equal to the negative logarithm of the hydrogen ion concentration or hydrogen ion activity.
Type of pH sensors
Combination pH sensors
The most commonly used method to measure the pH is to use an electrochemical pH-sensor. Combination pH-sensors are a type of electrochemical pH-sensor that contains both a measuring electrode and a reference electrode. The measuring electrode of the pH sensor detects changes in the pH value while the reference gives a stable signal for comparison. A high impedance device, known as a pH meter, is used to display the millivolt signal in pH units. The combined pH sensor technology can be used to build various products, including pH sensors for laboratories and industrial or process pH sensors.
Differential pH sensors
Compared to the combination of pH-sensors, differential pH-sensors have a slightly different effect. While combi pH sensors have 2 electrodes, one measuring electrode and one reference electrode, differential pH sensors have 3 electrodes. In the differential design, 2 electrodes measure pH differently from a third metal mass electrode. This design has the advantage that it prevents reference contamination, making it ideal for industrial applications such as wet air scrubbers;
Laboratory pH sensors
Combinations of pH sensors in 12 mm glass and plastic housings are commonly referred to as laboratory-style sensors. These sensors work well in light applications such as education and research, environmental sampling and pool monitoring. Although the basic design is the same, functions such as sensor fill, nodes and cables can be adapted to different application needs.
Process pH sensors
Combination of pH sensors can also be installed in larger, more robust enclosures with built-in process connections (such as NPT wires). These sensors are commonly referred to as process pH sensors and are ideal for continuous monitoring of the pH value. Process pH sensors are usually mounted in a pipe, immersed in a tank or used as part of a feeding system.
How are pH measurements used?
pH measurements are widely used to monitor processes, ensure product quality and safety.
- pH-neutralisation of effluent in industrial production environments
- pH control for cooling tower and boiler control
- Environmental monitoring
- Odour washers / air washers
- Quality control and safety of food and beverages
- Upstream protection of filtration membranes
- Water pre-treatment for production processes
- Control of the pool
- Pulp and paper production
- Pharmaceutical research & development and production
- Blood gas analysis in medical devices