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Above all hygienic: Command and signalling devices for food industry machines

Author : Siegfried Rüttger, Industry Manager Food & Packaging, Schmersal Group

26 February 2018

The N program control elementss –  in the new mushroom push button NDTP30 –  were developed for the requirements of the food processing industry.
The N program control elementss – in the new mushroom push button NDTP30 – were developed for the requirements of the food processing industry.

Hygienic design and ergonomic operation: These are the core requirements that apply to the man-machine interface of food industry machines. That is why the Schmersal Group has developed control elements and systems specifically for these industries. 

At the heart of the requirements for control elements for food industry machines is the "hygienic design". This means: No dust pockets may be able to form in and on the control elements in which product residues could settle, which would then form a breeding ground for bacteria and germs. The control elements can therefore be easily recognised by their special geometry with rounded shapes. In food processing operations, the daily cleaning of machines with high pressure or steam emitters is an absolute must. The control elements must therefore be equipped with a suitable sealing concept, which must not only be resistant against water jets and high water pressure at high temperatures, but must also insensitive to particularly aggressive cleaning agents. All devices must have a protection rating of at least IP69.

A program specifically for the food industry

The command and signalling devices of the N-program from Schmersal, developed specifically for this application, fully compy with this requirement profile: The abbreviation "N" stands for the food industry. The product family consists of a large range of command and signalling devices and a variety of accessories: Emergency stop push button, mushroom push button, push button, illuminated button and light, selector switch, main switch etc. plus accessories. The tried and tested program is continually expanded and improved.

The innovations include the NDTP30 / NDLP30 mushroom push button in an ergonomically improved form. Due to its large round button area, it is easier to operate compared to simple push buttons. The enlarged operating surface simultaneously protects the moving seal located underneath against damage. The 3-colour LED module ELDE.N provides the conditions for displaying three different signals or control commands with a single standard signalling device. This enabled the designer to reduce the operating unit. The number of surfaces which are potentially at risk of soiling is also reduced. The reduced number of operating and display elements also saves costs and improves the operator's overview.

A completely new development is the hygienic crossover switch of the NK series. The NK-crossover switches offer the machine designer completely new possibilities in machine design and machine operation. A special sealing concept enables the crossover switches to be installed completely open, depending on the application. The crossover switch offers the high degree of IP69 protection for the front panel and IP67 protection on the rear side which makes the complex inner cladding of the switching contacts unnecessary. The reed technology used also does not change the size of the device as a function of the switching contacts. The new crossover switch is equipped with an M12 connector, which ensures fast electrical connection.

A further highlight in the N-program is the combination with the new position switch PS116. This solution comes into play when an open machine concept is used or the formation of condensation water inside the machine impairs normal switching contacts and premature failure due to corrosion can be expected.

Tried and tested for hygienic-sensitive applications

Schmersal also offer ready-to-connect NBG mounting housings for the man-machine interfaces of food machines
Schmersal also offer ready-to-connect NBG mounting housings for the man-machine interfaces of food machines

The control elements of the N program fulfil the requirements of protection class IP 69K and have been tested by the DGUV Testing and Certification Centre "Food and Packaging" for their suitability for hygienic-sensitive applications. The tests show that the control devices can be used, for example, in meat processing without the risk to hygiene. The corresponding test certificate is regularly updated as the requirements for the devices are constantly adapted and tightened. In addition, the Fraunhofer Institute IPA has tested devices from the N - program with regard to their suitability for clean-room applications. The result: The tested command and signalling devices are suitable for use in production areas with the highest clean-room classification (air purity class 1 according to ISO 14644-1). This qualification certificate is also a declaration for recommendation to use in production environments for sterile preparations up to GMP Class C according to the EC GMP guide, Annex 1.

Complete control systems for demanding applications

The N program product portfolio also includes the provision of command and signalling devices with a blue sealing membrane. They fulfil the requirement for easy detection of foreign bodies in foodstuffs by means of optical systems. Blue has become the "signal colour" in the industry, because no food is this colour by nature. Only food-grade materials have been used for these devices.

Typically, the N-program command and signalling devices are installed on the control panels in the working area of the food machine or, directly on the machine housing where only an on/off switch and a signalling light are required. Food Technology Thielemann design engineers have developed an innovative solution. They partially integrate the man-machine interface into the hygienic control cabinets of their poultry processing machines and install the command devices in a hygienic NGB housing on the machine. According to information provided by the company, this design is currently being used in Brazil, where rigorously strict hygiene requirements exist.

Schmersal also offers complete ready-to-connect control systems for food machines using the N program. The basis for these systems are the stainless steel housings in the NBG series. They are also designed according to the principles of the "Hygienic Design" and offer space for one to five control elements. All materials used are food industry compatible. The seal between the upper and lower parts of the housing and the attachment to the machine was designed in compliance with the requirements profile of the food technology: There are no dead spaces in which dust pockets could form. The cable and cable entry has also been integrated into the bottom of the lower part of the housing, so that no cables and lines have to be routed into the housing through the hygienic critical area. The housings are equipped with command and signalling devices as required by the customer, who can then install the operating units as "plug and play".

The N-program control devices and the NBG body housings are used on machines for the processing of fish and poultry, e.g. installed in "on board" fish cutting plants and poultry meat slicers. Both areas place particularly high demands on the "hygienic design" and the stability of the man-machine interface to withstand frequent intensive cleaning, even with aggressive cleaning media.

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