Hygienic sensor solutions: Immune to germs and bacteria

Not all publicity is good publicity write Christian Freudig, product manager Business Unit Photoelectric Sensors & Fibers, Global Business Center Presence Detection, and Marco Kaiser, strategic industry manager for Consumer Goods – Packaging, Global Industry Center Factory Automation, both at SICK AG, Waldkirch, Germany. Product recalls and public warnings published by health authorities are published on a regular basis – often several times a week. Bacterial contamination in the production, transport, and packaging processes is one of the possible causes. A hygienic system design – and in particular hygienic automation components – can minimise the contamination risks for products and communication risks for manufacturers: Germs and bacteria do not stand a chance against stainless-steel sensors and system solutions from SICK.

Stainless-steel sensors from SICK deliver exceptional performance combined with compact dimensions, chemical and thermal material resistance, and lasting impermeability. Furthermore, all of the opto-sensory device types in the photoelectric sensor product families, for example, are also available in stainless-steel versions – energetic photoelectric proximity sensors, photoelectric proximity sensors with background suppression, through-beam photoelectric sensors, and photoelectric retro-reflective sensors. The stainless-steel sensor portfolio from SICK also offers suitable solutions for safety technology tasks, the identification of products and containers, position monitoring and path measurement, pressure, temperature, and level measurement, or the inspection of packaging and its contents. These solutions offer the highest level of process reliability for the manufacturer and maximum product safety for the consumer. At the same time, they ensure reliable functioning and consistently high levels of availability even under the harshest application conditions – because the automation tasks must not impact negatively on the hygienic design.

Product contamination: Three hazard zones in practical applications
Hygiene-compliant sensors “shine” not only on account of their stainless-steel housing but also as a result of numerous other measures that guarantee the best possible chemical and thermal resistance as well as impermeability. These reasons – and the lower quantities compared to standard sensors – justify a correspondingly higher price level. It is therefore worth taking a look at practical examples such as a cutting and processing machine in the meat industry, a dairy machine for cheese production, or a filling and

capping line in a beverage bottling plant. Each case involves typical plants that have to be cleaned and disinfected on a regular basis to prevent hygiene risks resulting from intermediate or end products becoming contaminated with microorganisms, spores, or inorganic residues. In terms of possible contamination risks, the machines and plants can be divided into three hazard zones, with corresponding consequences for the components that are to be used there. Zone C is the non-food area of a machine where sensors can be protected by covers, for example, or mounted in such a way that they cannot come into contact with food. Standard sensors can therefore be used in this zone to enable economically efficient automation solutions. Zone B is the area of a machine where external surfaces and plant components are cleaned with cleaning agents and disinfectants. In this area, standard sensors cannot withstand the required cleaning and disinfection, for example with surfactant, acidic, chlorinated, and chlorine-alkaline foam cleaners, or neutral disinfecting agents or those containing hypochlorite or peracetic acid, as well as the use of high-pressure cleaners with pressures between 80 bar and 100 bar. Stainless-steel sensors and components in a wash-down design are the ideal solutions in this case. They offer the required robustness and are designed (e.g., with beveled surfaces or rounded edges) so that cleaning and disinfection media can run off leaving as little residue as possible. Sensors used in Zone A – where they are in the immediate vicinity of the product – also undergo extremely demanding cleaning and disinfection processes. In addition, however, they must also meet special hygiene requirements and comply with recommendations, standards, ordinances, and regulations relating to hygiene. These situations call for stainless-steel sensors with a hygienic design, which offer maximum protection against germs and contamination risks.

Hygiene as a chain of competency: Safe sensor solutions with no weakest link
The portfolio of stainless-steel sensors and accessories from SICK offers hygienic solutions for flexible automation, protecting machines and processes, for quality control, and for identification applications. To ensure the continuous and long-term safety of products and processes, it is necessary to meet a variety of requirements with regard to the chemical resistance, thermal resistance, impermeability, and structural design of the stainless-steel sensors while adhering to market standards. These are interrelated like the links of a chain, where the weakest link will determine the suitability of the sensor or system solution for hygienic applications.

Design and material – maximum material durability for a long service life
When it comes to material durability against chemical substances, media, and gases, stainless steel 1.4404 / AISI 316L – which is suitable for housings and mounting components – offers maximum corrosion and pressure resistance. At the same time, the material supports the natural mortality rate of bacteria and other microorganisms on the surface of the components. Furthermore, the surface roughness is reduced to a value of Ra = 0.8 µm by means of machining processes such as electropolishing for hygienic applications. This reduces the adhesion of product and media residues as well as germs. Silicone seals, which SICK uses, for example, to implement a double sealing concept for photoelectric sensors, feature very broad chemical and thermal resistance. The construction of the device is also a key factor when it comes to ensuring hygienic design. A seamless housing design, smooth transitions to front screens, operating and visualization components on the sensor, and rounded edges and beveled surfaces aim to reliably and permanently eliminate the residues that act as breeding grounds for bacteria and other microorganisms.

Thermal resistance even in the event of extreme temperature fluctuations
In practice, the thermal resistance of the sensors is closely linked to material durability, because the temperatures of cleaning media (up to +80 °C), water vapor, and spray water can fluctuate very sharply and also very quickly, depending on the process. Furthermore, ambient temperatures of less than 10 °C can often occur in the machine’s wet area. All these factors place great demands on the sensor housings and seals – but also on the electronics. For this reason, the electronics of the stainless-steel sensors from SICK are designed and embedded in the housings in such a way that thermal overloading is reliably prevented, even under these tough conditions.


Hermetically sealed to the outside world
Particles in the ambient air, humidity, steam, condensation – all these factors can impair the function of sensors. Particular attention should therefore be paid to the impermeability of the sensor housings. In stainless-steel sensors from SICK, the housing, cover, controls, and front screen therefore form a strong and permanently tight seal. This is due to the special dual seal concept which reliably prevents particles and moisture from penetrating into the sensors. The concept is based on the use of seal materials that are resistant to heat and chemicals and are combined with specially selected high-performance adhesives. Depending on the sensor and application, it meets the requirements of enclosure ratings IP67, IP68, or IP69K. This enables the stainless-steel sensors as a whole to reliably withstand the aggressive external cleaning methods used on the systems. Properties such as the pressure and application distance of a high-pressure jet or the contact duration and temperature of the cleaning or disinfection media do not impair the function and long-term availability of the stainless-steel sensors – even in the long term. This is evident not only in practice, but also in SICK’s long-life tests based on its own practice-oriented test criteria.

Market standards – hygiene regulations provide the framework
The overarching link in the hygiene competence chain is the implementation of and compliance with hygiene recommendations (such as those of the European Hygienic Engineering and Design Group (EHEDG)), market standards, and specifications from agencies such as the FDA or American 3-A Sanitary Standards Inc. Consequently, SICK takes design requirements into account right from the development stage when working on new hygienic products and their mounting systems. These requirements are stipulated in the B standard DIN EN ISO 14159:2008-07 for machinery with general hygiene risks, and in the C standard DIN EN 1672-2: 2005+A1, which is specifically for food processing machinery. The same applies to Regulation 1935/2004/EC on materials and articles that are intended to come into contact with food, and Regulation 10/2011, which refers specifically to plastic materials and articles intended to come into contact with food. They all aim to ensure the safe production of food, beverages, and pharmaceutical products.

Material selection and processing, constructive design, implementation of market standards, as well as hygienic operation and automation functionality – the hygienic design of stainless-steel sensors from SICK incorporates extensive expertise in the fields of food, beverage, and pharmaceutical production. For a hygiene chain with no weak link.