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The safe food chain

The safe food chain

In the food and drink industry, achieving a safe food chain all the way from producer to plate is paramount. Maintaining hygiene levels is a critical element in the journey through a process plant, but one pinch-point that's easily overlooked is sensor hygiene.  Phil Dyas, industrial sensors UK product manager for SICK explains how better attention to the smallest details could save costs and improve productivity.

In the iconic 1960s classic film Fantastic Voyage, a team of scientists are shrunk to microscopic size and, in a mini-sub, are injected into a dying diplomat's blood stream to do some tricky surgery. The film has inspired a number of spin-offs since then. What if a film were made of a microscopic journey around a harsh industrial processing environment?  

Would a team of intrepid production engineers be surprised by what they find on their journey? Washed through pipes, past valves, pumps, joints and sensors, battered by swift flows, heated and corroded by aggressive cleaning fluids, they may well get a better insight into the design and efficient operation of
their plant.

They would see at first hand the tiny details of the hardware they are trying to keep hygienic to meet their customers' quality and shelf-life requirements. At millimetre and micron scale, every tiny wrinkle in a joint weld, corner in an angle change, or even a scratch in a pristine surface could become a dwell where particles can get trapped, sticky or viscous ingredients stick and even the most aggressive and high pressure washdowns fail to consistently penetrate. They can form the nucleus for bacterial or fungal growth which may ultimately cause quality defects, ill health in consumers and even plant shutdown.

In truth, no plant can be designed and maintained at economic, absolute 100% contamination-free performance levels; we have to aim for such low levels that the contamination has no appreciable result.

So it makes sense that all equipment in touch with the foodstuffs and beverages must be designed and manufactured to make it as easy as possible to achieve near-perfection in hygiene. That's the premise driving such standards as EHEDG (European Hygiene Engineering and Design Group), and the USA's 3-A Sanitary Standards and EcoLab approvals and certificating systems, and in meeting standards such as IN ISO 14159:2005-07 on general hygiene principles for machinery design, and EN 1672-2:2005+A1 which focuses on foodstuffs.

Food processing is a demanding industry with a tough supply chain to satisfy. The demand for longer shelf lives for packaged foods is one of the biggest challenges, which in turn has a direct impact on packaging and cleaning processes as well as the design of machinery.
Supplying contaminated or inedible food can result in considerable financial losses and serious damage to a company's reputation. However, compromising on productivity or machinery up-time is simply not an option.

At the same time as being constructed from rugged materials that withstand harsh chemical and high temperature washdowns, sensors still need to meet engineers' demands for high performance with compact dimensions, as well as quick, easy installation and commissioning.

All too often I have seen food processing environments where 'big ticket' cooking and handling equipment meets the highest hygiene criteria but the same scrutiny is not carried through to sensors and their mountings and fixings. A chain is only a strong as its weakest link.

Some specifiers wrongly assume that a standard stainless steel or plastic sensor will satisfy hygiene requirements because it is easy to clean the surface. As a result, many optical sensors used in essential tasks such as product and pack positioning on conveyor belts, proximity sensing or triggering pick-and-place are wrongly specified. Even if the right sensor is specified, then a fixing or mounting might be chosen that is not to the same standard.

Let's be clear: it's not that a sensor may be poorly-designed; just wrongly specified for the environment in question. I have come across many engineers who just expect a sensor to fail in months or even weeks. Because they may have a low capital replacement cost compared to the rest of the hygienic plant, they are treated almost as consumables which get submerged in the high running cost of hygienic plant.

Replacing wrongly-specified sensors could cost a factory £1000s a year in an industry with very tight margins. I have even witnessed engineers putting plastic bags or yoghurt tubs around sensors whenever the cleaning takes place, or drying them out on radiators afterwards.
Lower grade sensors may not be capable of withstanding frequent washing with harsh solutions containing chlorine or hydrogen peroxide. These solutions may also degrade under specified seal materials, particularly where joint design allows solutions to collect and concentrate. If seals or plastic mountings become degraded and cannot be effectively cleaned any more, then sooner or later the internals will be affected.  

Wide fluctuations in temperature from hot flushing to refrigeration may cause considerable stress to materials, seals and internal electronics. Water ingress can also be caused through the 'pump' action initiated by rapid temperature swings.

So what should anyone responsible for specifying sensing equipment in food and beverage processing or other high-hygiene environments be looking out for?

Firstly, of course, that the designs are in accordance with the latest international standards. If casings are not seam-free, all joints should be designed so they are capable of being sealed with edges that are flush. Corners should be rounded, ridges rounded and joint seals made of appropriate materials that resist contamination, like silicon rubber. Wherever possible, LED indicators and switches must be completely flush.

Importantly, sensor mounting and fixings, cable entries and other parts must also be designed with these standards in mind. There's not much point having the front face apparently hygienic when, a few centimetres around the back, a dirt trap actually protects contamination build-up from being washed off.

The relevant environmental protection standard is IP69K which signifies that a piece of equipment can withstand high pressure, close-quarter, hot (80°C) sprays for a series of test of 30 seconds duration.

However cumulative effects of chemicals and expansion/contraction could compromise the materials and construction. This means that IP69K should be regarded as a starting point for the specification, not an end in itself.

For this reason, it is also important for specifiers to appreciate the difference between sensors constructed to be resistant to cleaning and washdown, and sensors that are designed for 100% hygienic environments. The essential difference in features between the washdown and hygienic versions is that a hygienically-designed sensor is built for use on the process side where the sensor will come into contact with, or in the direct vicinity of food. However, if in doubt, it's always best to consult the manufacturer and to choose a supplier with specialist knowledge of food and hygiene environments.

SICK's solutions are focused on two ranges, depending on the level of hygienic protection required. SICK calls the product groups INOX and Hygienic.  Sensors such as the new W4S-3H photoelectric sensor family offer best-in-class detection performance in both Inox and Hygienic versions.  

SICK INOX range of sensors, systems and instruments have a compact and rugged IP69K housing in high grade 1.4435 / AISI 316L stainless steel and PEEK plastics such as VISTAL to withstand the harshest washdown, disinfection and cleaning regimes as well as the fully resistant mountings and fixings. They are durable, waterproof and chemical resistant products to withstand clean-in-place (CIP) and washdown procedures with IP69K class ingress protection.

SICK Hygienic products are made of high-grade stainless steel and specially-designed with completely smooth external housings with no edges, corners or ridges that could attract bacterial build-up or chemical contamination. Each is designed to enable liquids to run-off slowly, allowing maximum contact with cleaning agents whilst leaving no liquid residue.

New Hygienic variants of the well-proven SICK LFP guided radar level probes, LVF tuning forks for level detection, PHT/PBS pressure and THT temperature transmitters now add breadth to the SICK Hygienic range.

Where safe guarding between hygiene zones is a concern, and protection of personnel from moving machinery, light curtains such as the C2000 are available in INOX housings with full IP69K protection, for example on conveying systems between processing and storage areas.

Vision cameras are increasingly used in quality control in the modern, highly automated food and drink processing plant, and the hygienically housed IVC3-D camera delivers real time quality control and positioning information in pick-and-place operations. These can be teamed with the hygienic area DFS601 encoders for precision conveying speed measurement of the line.

For complete confidence, SICK offers compatible stainless steel mountings, reflectors, tubes and flanges all made to the same stringent standards without compromising on performance or ease-of-use. Quick to install and replace, the 'turn and click' connector for the WS4-3H sensor, for example, meets the highest European and FDA standards and resistance to chlorine-based disinfectants, detergents and foam cleaners.

SICK's dedicated product development teams work with standards authorities and food and pharmaceutical manufacturers to ensure that products not only comply, but exceed, requirements to deliver true value in long-term plant operation, not just the best price.

Although purpose-designed hygienic sensors could be 30-40% more expensive than standard designs, a correctly specified sensor will have paid for itself in less than six months, compared to one that needs frequent replacement. Sensor and mountings properly-specified for the environment avoid the risk of compromising hygiene and aid productive operation.

Sick (UK) Ltd

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