An Introduction to Industrial pH Measurement

What is pH? pH, which is the measurement of hydrogen ion concentration, describes the degree of acidity or alkalinity of a solution. pH measurement as well as pH control is a critical factor in a wide range of industrial applications – including pharmaceutical manufacturing, food and beverage production, dairy and agriculture, water treatment applications, and countless others – and pH control is often vital in ensuring the quality of a product.

The term “pH” – derived from the mathematical symbol for a negative logarithm (p) and the chemical symbol for Hydrogen (H) – stands for “potential of Hydrogen” and is, as mentioned just previously, the measurement of hydrogen ion concentration in a liquid solution. pH is a determined value based on a defined scale, similar to temperature.

The pH scale is logarithmic – as it inversely indicates the concentration of hydrogen ions in the solutions – and ranges in value from 0 to 14. A solution with 10-8 moles of H+ ions per liter has a pH value of 8; a solution with 10-2 moles of H+ ions per liter has a pH value of 2 – and so on. Solutions with a low pH value (0-6) are classified as acidic while solutions with a high pH value (8-14) are classified as alkaline. The middle value (7) represents pure water, which is neutral – neither acidic nor alkaline.

Why is pH Important in Industrial Application?

pH levels are an important variable in a wide range of industrial applications – and, as quality is often dependent on consistent, optimal pH levels, it is a variable that requires effective monitoring and control. If pH levels are not monitored and controlled effectively, food products may become inedible, beverages may become undrinkable, soil may become unusable, and wastewater can have an undesirable effect on the environment. Accurate, consistent pH measuring, therefore, is often essential for successful industrial product manufacturing.

Measuring pH

Since the knowledge of pH is critical in a myriad of industrial situations, it is important to understand the different measuring options that exist. There are several ways by which pH can be measured, and they differ in many ways – most importantly in accuracy.

One option for measuring pH is to use a litmus strip. A litmus strip is a slip of paper that has been treated with certain chemical powders that, when in direct contact with a solution, will change color according to the pH level of that solution. However, the colorimetric method is not as accurate as pH measurement and control in industrial applications requires.

When more accurate measurements and continuous process monitoring and control is necessary, such as is the case in many industrial applications, a more sophisticated approach is required. For highly accurate pH measurement and superior monitoring and control capability, industrial process managers and operators utilize pH sensors – which are commonly referred to as pH electrodes.

pH Electrodes

pH electrodes are designed to allow hydrogen ions in the solution to pass through a selective barrier, commonly constructed of special glass, generating a measurable voltage differential between the pH measuring electrode and the reference electrode that’s proportional to the solution’s pH level.

At a pH level of 7 (neutral), for example, the electrodes will produce 0 volts between them. At a low pH level (acidic), a voltage will be developed of one polarity, and at a high pH level (alkaline), a voltage will be developed of the opposite polarity.

The pH electrode is connected to a pH meter, which is a high impedance amplifier that accurately measures electrode voltages and displays the results directly in pH units on a digital display.

Controlling pH

While measuring and monitoring pH levels is an essential aspect of many industrial processes, there is not much use to the effort if levels cannot be controlled. Using the data collected from pH electrodes and pH meters, an effective, automated pH control system can be constructed.

A pH control system measures the pH of the media and controls the automated addition of a neutralizing agent – which is known as a ‘reagent’ – by a pH controller. Adding the appropriate ‘reagent’ – as well as the appropriate amount – to media that is either too acidic or too alkaline will bring the pH levels back to within a desirable range. For example, when a high alkaline level is detected in process media, an acidic reagent can bring the pH level back down to the correct amount. Conversely, if a low alkaline level is detected, an alkaline reagent can be added to increase the pH level.

pH control systems depend on many variables – such as flow, acid or base strength, method of adding reagent, as well as physical requirements and limitations. As such, industrial pH control systems are highly varied and subject to particulars within each process system.

Summary

In industrial processing, pH measurement and control are essential in ensuring both product quality and that specific chemical reactions are occurring within the processing system. While applications of pH measurements vary widely, optimal and effective pH measurement and control can be obtained only through proper equipment choices and proper system design and execution. Industrial process systems operators and managers who rely on accurate pH measurement and control often turn to Omega Engineering for not only high-quality, state-of-the-art equipment, but for the expert advice available around the clock from Omega Engineers.

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