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Burkert Fluid Control Systems has revealed that its Type 8201 enamel pH sensors are ideal for use in high-end hygienic processes in biotechnology, pharmaceuticals and food processing.

The measuring system has a ’fit-and-forget’ design, which enables its sensor to stay in process, even during clean-in-place (CIP) purification.

The hygienic design and robust, glass-free construction of the 8201 pH sensor mean that the unit is suitable for use in high-end hygienic processes, for example, in the production of foods and active ingredients where the pH value of liquid mediums – including those that are viscous or contain solids – is measured.

Burkert said the 8201 provides long service life in these processes and high levels of accuracy, with its ability to measure absolute pH values between pH 0 and pH 12, at medium temperatures up to 140C, and process pressures up to 6 bar.

The 8201 pH sensor is said to be easy to use, and operates as a single-rod measuring cell with the measuring electrode and reference electrode combined in one element.

The sensor probe is a stainless steel tube, which also houses a Pt 1000 for temperature compensation.

It is coated with an ion-sensitive enamel layer, providing a smooth surface that prevents media from sticking during measurement, making the sensor easy to clean.

Unlike many glass probes, which have electrolytes that dry out in air, the 8201 sensor can be left dry as long as the user requires, without any drying out or loss of performance.

The electrolyte is stored in a separate electrolyte vessel and permanently connected to the electrode via a hose.

The pressure of the electrolyte vessel is maintained slightly above process pressure by means of an attached pressure controller.

The monitoring of the pH of liquid media in high-end hygienic processes ensures that legal requirements are met and also that quality standards are maintained, reducing cost and ensuring optimum levels of yield.

In these high-end processes, the life of the pH sensor is a tough one, typically having to withstand cleaning with acids and caustic solutions under higher temperatures, as well as steam purification.

Most pH measurement is carried out using glass electrode pairs and glass is vulnerable to both physical damage and chemical attack.

Strong acids and strong alkaline solutions attack the glass membrane of pH sensors, and even neutral solutions containing high concentrations of alkali ions – sodium ions in particular – also assault the glass.

Adding to these problems, the vulnerability of glass to chemical attack increases with temperature – for every 30C rise in temperature, the rate of attack increases 10-fold.

Consequently, electrode life is reduced when the pH sensor is used in process solutions at elevated temperatures, or when the glass formulation of the sensor is inappropriate for the sensed medium.

Glass systems also need special care against the effects of dehydration.

Left out of solution, a pH glass membrane will gradually dehydrate, which can affect its performance – the sensor will have slower response and higher-than-normal impedance when put back into operation.

Dehydration can also affect the operation of the reference electrode in glass systems, preventing proper operation.

The electrolyte can leach out of the electrode cavity, through the junction(s), forming salt crystals on the junction surface.

Over time, the leaching will weaken the electrolyte potential and may cause a phenomenon known as a ’bridging effect’.

Both of these conditions will increase the output impedance, making the output of the reference electrode instable.

Moreover, with continued dehydration the impedance will rise to a level that renders the pH meter unusable.

The limitations and special requirements of glass-based pH systems have led to the development of pH sensors manufactured from stainless steel and coated with enamel.

Compared with conventional glass electrodes, enamel-coated sensors offer a number of operating benefits, according to Burkert.

First, they are largely unbreakable and consequently less susceptible to errors in production.

Second, they can be CIP, saving users both time and cost, by removing the requirement for sensor removal, cleaning and recalibration.

Third, the sensor can be left dry for extended periods without any drying out or loss of performance.

Fourth, the enamel finish provides high levels of non-stick performance for maximised hygiene, while pH values are measured – and it can be used in media with a high proportion of solid particles.

Fifth, the sensors require recalibration only once or twice a year; maintenance is limited to the yearly exchange of the reference electrolyte supply bottle.

Sixth, the sensors have no moving parts or additional electric or pneumatic actuators so the complexity of central process control is reduced.

The ability of enamel pH sensors to allow CIP is particularly critical as sterility is key in ensuring that biochemical reactions can proceed cleanly with maximised sterility, and with no effects on the end product.

In contrast, opening up of the process – as was the case with glass sensors, where sensors had to be removed via special automated armatures and cleaned separately with chemicals before being recalibrated – risked bringing germs or contamination into the process.

Burkert Fluid Control Systems

Burkert Fluid Control Systems has been manufacturing products and systems for over 60 years that can be used wherever fluid media and gases need to be measured, controlled and regulated.

Burkert Fluid Control Systems has been manufacturing products and systems for over 60 years that can be used wherever fluid media and gases need to be measured, controlled and regulated.Whether the application is filling, level, flow, pressure or temperature we have a solution and a uniquely comprehensive range of products to handle it, including solenoid, process and analytical valves, pneumatic actuation, sensors and controllers.

For Burkert it is not enough to simply offer individual products.Our aim is to provide complete system and application solutions that meet the specific needs of our customers.Tell us what you need and our engineers will find an appropriate solution using our vast experience and a wide range of services such as advice and engineering, installation, testing, and after-sales support.

Burkert’s global presence offers our customers an additional advantage.Products and systems are constantly developed and optimised according to international standards.Through this process synergy effects evolve which ensure technological leadership and competitive advantage

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