Measurement and Control Instruments

What does a pH measurement and control instrument do?

pH measurement and control instruments continuously measure the acidity or alkalinity (pH value) of a liquid and control dosing pumps to keep this value within a set range. They are used in swimming pools, water treatment plants, cooling towers, irrigation and fertigation systems, and industrial process water applications. The model in this category is a single-channel pH measurement and control instrument.

How does it work?

The instrument takes measurements via a pH electrode immersed in the liquid or installed in-line. The measured value is displayed on the screen and compared with the set target value. When the pH value deviates from the target, the instrument activates the dosing pump feeding the appropriate chemical (pH reducer or raiser) and stops it when the value returns to the range. Some models also feature alarm outputs and signal outputs.

Selection and installation

• Measurement range and accuracy: Must meet the accuracy required by the application.
• Outputs: Relay or signal outputs for controlling the dosing pump must be appropriate for the application.
• Electrode: An electrode compatible with the temperature and chemical composition of the liquid to be measured must be used.

The electrode must be positioned at a point where the liquid is well mixed and sufficiently far from the dosing point; otherwise the measurement will be misleading.

Calibration and maintenance

pH electrodes become fouled over time and lose their accuracy; calibration with buffer solutions must be carried out at regular intervals for accurate measurement. The electrode tip must not be allowed to dry out and should be kept in storage solution. The service life of the electrode depends on operating conditions and it will need to be replaced after a certain period.

Frequently asked questions

Why is pH value important?

It directly affects disinfectant efficiency in pools and corrosion and scale formation in pipework.

How often should calibration be performed?

It varies according to operating conditions; the intervals recommended by the manufacturer should be followed.

Does the instrument work with a dosing pump?

It is used together with a suitable dosing pump for control.

Is the electrode sold separately?

Whether the electrode is included with the product is stated in the product description.

Is it suitable for pools?

Pool pH control is one of the most common applications for these instruments.

Can chlorine also be measured?

This single-channel model is for pH measurement only; a separate instrument is required for chlorine measurement.

What supply voltage does the instrument operate on?

The supply voltage is stated in the product information. If the installation is to be made inside a panel, it is recommended that the electrical connection be carried out by a qualified person.