pH Electrode
Various methods of pH measurement are available but the most sensitive and accurate method suitable for industrial use is the pH glass electrode. A combination pH electrode comprises of two millivolt generating components;

The pH sensitive glass bulb which generates a millivolt signal that changes with the pH of the sample solution. A specially formulated glass sensitive to hydrogen ions is used. Inside the electrode is a solution with a constant pH value with an internal conductor immersed in the solution and connected to the electrode lead. If the hydrogen ion concentration is greater in the sample solution being measured than inside the electrode then a positive difference will exist across the glass bulb.

If the measured sample is lower in hydrogen ion concentration then a negative potential will exist.

The Reference must also make contact with the sample. This part of the electrode generates a stable millivolt signal irrespective of the pH of the sample solution. There are two main types of reference electrodes: Silver / Silver Chloride and Mercuric Chloride (Calomel HgHg/Cl). With a Silver / Silver Chloride reference the connecting wire is connected to a Silver wire which is coated with Silver Chloride. This is in a solution of Saturated Potassium Chloride (KCl), the Saturated KCl called the salt bridge in turn contacts the process solution through a liquid junction which can be a ceramic frit or fibre wick.

The pH meter receives the two millivolt signals from the pH electrode and subtracts them from each other. The pH meter amplifies and converts the millivolt signal to conventional pH units for display and transmission.

The pH electrode produces 59.16mv per pH unit with the pH electrode having an Electrode output of 0mv at 7pH, the neutral point between Acidity and Alkalinity. This is sometimes stated an E0 value of 7pH. A positive mv electrode output indicates an Acidic condition which is represented by pH values less than 7.0pH while a negative mv output signal indicates an Alkaline solution with a pH value greater than 7.0pH.

LTH Electronics offer a range of pH electrodes to suit most process applications in many different configurations for tank or pipe mounting applications. Self-cleaning and spray wash adapters can be fitted to the pH electrodes to reduce maintenance in waste streams that normally coat the electrode.

Call us on +44 (0)1582 593693 or email sales@lth.co.uk to find out how we can help you.