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.
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
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.
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.
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
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