Relative pH-measurement principle
Differential pH probes provide values measured against a product-dependent reference parameter. The measured value is therefore a product-specific value (relative pH-measurement) that allows a statement as to whether a process is performed according to defined specifications. This measured value is therefore ideal for controlling and monitoring recurring batch processes (e. g. formulations without changes) or continuous measurement. Differential pH probes are simple in structure: two ion-sensitive enamels are fused onto a steel probe carrier and form the measuring part of the sensor. One sensor surface responds to H+ ions and provides a potential that depends only on the pH value; this is called the pH glass.
The other sensor surface – the reference glass or reference electrode – responds to the salts dissolved in the liquid, especially the Na+ ions resent, and thus provides a product-specific reference potential. Once the transmitter has been configured with data from the measurement and test report provided, the pH differential probe is calibrated in its installed position using a product sample.
The probe then works like a “normal” absolute pH-measurement device in the specified range. The special relative measurement principle means that the probe functions without an electrolytic liquid. This eliminates the risk of the product being contaminated by the electrolyte and ensures practically maintenance- free operation.