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 Parameter / pH-value 

Basics

The pH value is an intrinsic value of all aqueous solutions: Each aqueous solution has a pH value. At 25°C pure water contains H+ and OH-  ions in equal amounts.This state is called neutral with a pH value of 7. The pH scale covers values between 0 and 14. Acids have pH values towards 0, caustic solutions have pH values towards 14.

pH values - examples

 

battery acidpH < 0
ColapH 2-3
orange juicepH 3.5
winepH 4.0
teapH 5.5
human salivapH 6.5 - 7.4
sea waterpH 7.5 - 8.4
bleaching solution pH 12.5
caustic SodapH 13.5 - 15

 

Applications

The pH value is important in almost any area concerned with water: The European drinking water directive demands a pH value of 6.5 – 9.5 for drinking water both for hygienic and technical reasons. Water with pH lower than 6.5 can cause corrosion of metal pipes and give rise to high concentrations of heavy metal ions in drinking water. Corrosion is also a very important issue for cooling towers and boiler feed water and in fact for any water in contact with metal pipes and tanks. For swimming pools hygiene and health are the main reason for restricting the pH value to 6.8 – 7.6. Too high values affect the disinfection process, and too low values may lead to skin irritation. Industrial waste water has to be neutralized prior to release into the sewer system.  In waste water treatment the pH value is controlled to remove heavy metals or to optimize ORP reactions such as Chromate reduction, followed by neutralization. In process water the pH value is one oft he most important parameters. It can affect product quality and production efficiency. It might even be vital for a chemical reaction such as polymerisation.

 

Dr. A. Kuntze measurement

diagram sensor

pH is measured potentiometrically with glass sensors. The sensor contains a pH-sensitive glass membrane on the surface of which alkali ions are exchanged against H+, leading to a changing potential that depends on pH. The potential is measured against a reference. Modern ph glasses hardly respond to interfering ions such as sodium over a wide temperature range. We use three different pH-sensitive glasses with the following characteristics: AH – High alkali / high temperature glass: Measuring range pH 0-14. Very low alkali error. With liquid filling applicable up to 100°C. LT  – Special glass with very low resisitance: For cold water applications. Resisitance reduced by 90% compared to AH. Measuring range pH 0-12 at temperatures of  -5 – +60°C. S  – Fluoride-resisitant glass: For applications with high fluoride concentrations. Tolerates up to 500mg/l Fluoride over the measuring range pH 1-11 at temperatures up to 60°C.

 

You would like to measure pH in your application?

Select one of our measuring insturments– either you choose our single-channel instrument series K 100 or our two-channel instrument series dialog. Therunto one of our high-quality pH-sensor (make your choose with our product  navigator), a immersion or flow assembly  and one of our sensor cable -if desired or required - our impedance converter IWA 11.4. An IWA is useful for larger distances between electrode and instrument or under unfavourable installation conditions.

measuring point - flow
measuring point - immersion

Sensors
We can offer a suitable pH-sensor for almost any application. The necessary characteristics are determined by the components.

Glass is not just glass

The pHsensitive glasses used for the pH electrodes are produced by well-kept formulas of the Kuntze family. The formuals are passed from generation to generation and today they are refined in the third generation. With the pH-glass you define the fluoride resistance, the temperature resistance, the alcaline error, and the electrical resistance.

For a long life...

The life time is determined by adaption of the sensor to the application s. An adaption of the internal buffer in acidic media reduces the measuring error, a double chamber prolongs the life-time, whereas a liquid electrolyte is an important feature for stable measurements in ultrapurewater. Search for the suitable sensor for your application in the corresponding sensor group. but for all that we´d like to advice you in a personal dialog.