Online pH measurement
for process control

Online pH measurement is necessary in almost all industrial processes containing water. The pH value is an important parameter to be measured and controlled. Automatic pH control systems are used to optimize processes, reduce corrosion and scaling in plant equipment, and to protect the environment and groundwater from polluted wastewater.

pH loop

online pH measurement

For online measurements, we talk about a so-called pH measurement loop, or pH loop. A pH loop is made up of three components, the pH electrode, the pH transmitter, and a cable to connect the electrode to the transmitter.

The reason we use the term transmitter, and not a pH meter, is that a transmitter has some form of a communication interface which can transmit data to a control system or a computer.

Chemically aggressive environment

To pick and install the right equipment to get a trouble-free operation is not always an easy task for process pH control systems. Industrial pH probes lead a hard life. In chemical processes, they may have to withstand strong acidic or caustic solutions under high temperatures. However, not only the electrode but also the transmitter, the cables and connectors have, in many times, to withstand an aggressive environment.

The aggressive nature of many process pH applications means that periodic maintenance and checking are required to ensure accurate and trouble-free measurements.

Process pH measurement considerations

Regardless of whether a pH measurement is done in a laboratory or in a process plant, it is important to understand how the measurement is made, how to calibrate and how to recognize and avoid common problems. How the electrode and the pH meter works and how to maintain and calibrate the pH electrode is already described on this web site. However, there are some specific things regarding online pH measurements that we need to address:

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industrial pH probes