Keeping computing systems in food plants clean

Computers in food plants have to be cleanable so they don’t add any contamination load to the end products. So they must be able to withstand the cleaning and sanitation regimes of the plant.

The food industry relies heavily on computer-based control systems and human-machine interfaces (HMIs) to automate and control manufacturing and other processes and also to communicate with human operators. These computers are frequently out in the plant itself and so must be able to withstand the food plant environment and be able to be kept clean so they do not contribute any contamination potential to the foods or beverages.

This means that the equipment will be periodically subjected to high-pressure washdown and exposed to cleaning and sanitising solutions to protect against biological contamination of the end product.

Sealed computer or sealed enclosure?

The deployment of computer equipment in such washdown environments presents a particular set of options and trade-offs to the system designer. One key issue is whether to specify a sealed, industrially hardened computer that’s ready to deploy in a washdown environment or to specify an appropriately sealed industrial enclosure into which a more general-purpose computer can be placed. Either approach can perform admirably when it comes to the basics of routine operation: meeting the process’s sanitation requirements while protecting electronic equipment from water sprays and temperature extremes. Over the long term, however, the choice between the two is an investment decision that must balance life cycle costs, operational continuity and the accelerating pace of information technology.

Equipment protection in industrial environments

The IP (International Protection Code and Ingress Protection Code) rating for equipment or enclosures gives a quantifiable measure of protection against intrusion by either solids or liquids.

The IP Code, specified in Australian Standards AS60529 and also EN60529 and IEC 60529, consists of two numbers and an optional letter, eg, IP67. The larger each digit, the greater the protection.

The first digit represents the level of protection against solid objects. It ranges from 0, which means no protection, through protection against large objects such as hands (1) to total protection against dust ingress (6).

The second digit in the code represents protection against liquid ingress. Once again, 0 implies no protection. Numbers 1 to 6 give increasing protection from falling drops of water through sprays up to high-pressure water jets.

A rating of 6 will cover you for ratings 1 to 5 for both solid and liquid protection.

Liquid protection ratings of 7 and 8, however, are separate. These digits give a measure of protection against immersion but do not imply spray protection as well.

There may be additional letters after the two digits. These letters can be appended to classify the level of protection against access to hazardous parts by humans. For example: A - back of the hand, B - finger etc.

Further information can be appended that relates to the protection of the device: H - high-voltage device, M - device moving during water test etc.

The standard does not specify standards of protection against risks of explosions or conditions such as moisture (produced, for example, by condensation), corrosive vapours, fungus or vermin.

IP69K and the food processing industry

The IP Code does not cover enclosures that are subjected to high-temperature and high-pressure washdowns such as those found in the food industry. The Germans issued standard DIN 40050-9, which extends the IEC 60529 rating system with the IP69K rating. Initially developed for road vehicles, especially those like cement mixers that need intensive cleaning, IP69K is particularly useful in the food industry.

The IP69K test involves close range, low volume and very high pressure - similar to that experienced in the food and beverage industry.

Products rated to IP69K must be able to withstand high-pressure and steam cleaning. The test specifies a spray nozzle that is fed with 80°C water at 80-100 bar and a flow rate of 14-16 L/min. The nozzle is held 10-15 cm from the tested device at angles of 0°, 30°, 60° and 90° for 30 seconds each while the test device sits on a turntable that rotates once every 12 seconds.

Possibly the best advice is to buy a copy of the standard, decide what level of protection you, your equipment and enclosures need and then purchase equipment with the appropriate IP rating.

IP (1st digit)	Protection of equipment against solid objects	Tested by	Meaning for protection of persons	IP (2nd digit)	Protection against water with harmful effects	Tested by	Meaning for protection from water
0	No protection	None	No protection	0	No protection	None	None
1	Solid objects 50 mm	50 mm dia. sphere applied with 50 N force.	Accidental touch by back of hand	1	Vertically dripping	Drip box for 10 min.	Falling drops of water, condensation
2	Solid objects 12.5 mm	12.5 mm dia. sphere applied with 30 N force.	Accidental touch by fingers	2	Dripping - 15° tilted	Drip box, 2.5 min. per side	Direct light streams of water, up to 15° from the vertical
3	Solid objects 2.5 mm	2.5 mm dia. steel rod applied with 3 N force.	Accidental touch by tool	3	Spraying	Oscillating tube ±60°, 10 min., 10 L/min.	Direct sprays of water, up to 60° from the vertical
4	Solid objects 1 mm	1 mm dia. steel wire applied with 1 N force.	Accidental touch by small wire	4	Splashing	Oscillating tube ±180°, 10 min., 10 L/min.	Water sprayed from all directions, limited ingress
5	Dust-protected (limited ingress, no harmful deposit)	Dust chamber with or without under-pressure.	Accidental touch by small wire	5	Jetting	6.3 mm dia. nozzle from 2.5 to 3 m distance,12.5 L/min. for 3 min.	Low-pressure water jets from all directions, limited ingress
6	Dust-tight (totally protected against dust)	Dust chamber with under-pressure.	Accidental touch by small wire	6	Powerful jetting	12.5 mm dia. nozzle from 2.5 to 3 m distance,100 L/min. for 3 min.	Strong jets of water, limited ingress
				7	Temporary immersion	Immersed in tank with water 0.15 m above top and 1 m above bottom, for 30 min.	Protected against the effects of temporary immersion in water.
				8	Continuous immersion	Water level and time as specified by manufacturer.	Protected against the effects of continuous immersion in water.

The National Electrical Manufacturers Association (NEMA) has also developed classifications to make it possible to specify enclosure requirements. While similar to the IP rating the two methodologies are not directly interchangeable. The NEMA enclosure classification of specific relevance to washdown environments is 4X. The operative descriptors for NEMA 4X are protection against hose-directed water and resistance to corrosion. Corrosion resistance normally dictates stainless steel construction.

NSF International has also codified the essential characteristics of enclosures used in washdown environments in its NSF/ANSI (American National Standards Institute) standard 169 covering ‘Special Purpose Food Equipment and Devices’.

Essential aspects relevant to the enclosure’s ability to be thoroughly cleaned (and not harbour microbial contaminants) include lift-off hinges with removable pins; leg stands or easily cleaned casters with a minimum 150 mm unobstructed clearance; sloped surfaces to facilitate runoff; welded and deburred joints and seams; easily cleanable fasteners, including slot-head quarter-turn latches; and no exposed threads, projecting screws or studs.

Adequate thermal management is another fundamental design consideration - whether a sealed industrial computer assembly is used or whether the enclosure and computer are specified separately. After water, excessive heat in particular is a computer’s worst enemy. Some sealed industrial computers are designed to work without active cooling; this is intended to improve system reliability because no moving parts are involved, but may limit the unit’s ability to dissipate heat at higher ambient temperatures. Other industrial computer assemblies employ the same cooling technologies as stand-alone enclosures, including fans and heat exchangers, air conditioners and vortex coolers. Heaters, too, sometimes are dictated in order to deal with refrigerated processes and to avoid condensation within the enclosure.

What happens when the computer fails?

From a design and nominal performance perspective, there’s generally little to differentiate an industrial IP66 computer from a general-purpose computer in a separately specified IP66 enclosure. In general, the higher initial purchase price of the industrial computer will offset the costs of a less expensive, general-purpose computer and enclosure. If specified properly, either option will capably perform the task at hand.

While an industrially hardened computer should last longer, hardware failures do happen and these computers are often relatively inflexible when it comes to repair, and their sealed design may require a visit from the supplier’s service technician.

If, however, a non-industrial computer kept in an IP66-rated enclosure fails, repairs are usually simpler or a back-up computer more economically maintained in inventory.

Significantly in these days of fast technology improvements, by decoupling the protection element from the computer users can more simply and economically take advantage of advances in computing and software technology.