The engineer's guide to specifying plastic enclosures for IIoT sensors

Industry 4.0’s insatiable appetite for IIoT sensors has fuelled demand for plastic enclosures. They have gained traction in smart factories where metal housings would previously have been the first choice.

These plastic enclosures must be tough. In the past, ABS was popular due to its high impact resistance, dimensional stability and tensile strength. But ABS is vulnerable to UV rays; they can discolour and embrittle it. ASA is more UV stable. Better still is an ASA+PC blend that adds polycarbonate for extra strength. It also offers UL 94 V-0 flammability resistance.

Small, fast-fit sensor enclosures such as MINI-DATA-BOX and EASYTEC are moulded from ASA+PC as standard. Rated IP 65, they offer complete protection against dust ingress and can resist low-pressure (30 kPa) water jets.

Flanges make MINI-DATA-BOX and EASYTEC quick to install with cable ties or screws. MINI-DATA-BOX can also be specified without flanges, though it retains the distinctive ‘diamond cut’ lid design of the flanged version.

This weight-saving lid bevelling may be a subtle design touch but it shows how important aesthetics have become in the Industry 4.0 workplace. It gives MINI-DATA-BOX character but the enclosure remains discreet. Small is beautiful…but not ostentatious.

The proliferation of sensors in IIoT environments means that most must be wireless, enabling flexible deployment. Most engineering-grade plastics such as ABS, PC and ASA are RF transparent (though this in turn raises EMI/RFI issues).

RF transparency means that an antenna can be placed inside the enclosure. Alternatively, the flat sides can be machined to accommodate an external antenna for greater range or enhanced signal reliability.

Opting for an external antenna can also overcome some EMI/RFI interference issues — it is free to radiate signals outside the EMC-shielded enclosure. EMI and RFI can pose significant issues in RF-dense environments packed with wireless sensors, actuators, gateways, access points, controllers, RFID readers, NFC tags and machine-to-machine (M2M) links.

The large number of devices in IIoT networks highlights the need for an enclosure model that comes in lots of shapes and sizes. This makes it easier to specify the ideal housing and minimises the amount of customisation required.

One example is ART-CASE, a range of round, square, rectangular and obloid enclosures for wall/ceiling-mount, desktop and mobile applications. Ergonomic contours create a modern look and a shared design language. Options include a 30° or 55° sloping top as standard.

Increasingly popular are small wall-mount enclosures for touch screens. Elegant SMART-PANEL has been designed to fit standard flush-mount/cavity wall boxes. This — and the screwless assembly — makes installation swift and simple. Reopening is with a plastic tool set (accessory).

An alternative is DIATEC, which also fits flush-mount boxes but its smallest XS version (150 x 37 x 155 mm) is three times the size of the biggest SMART-PANEL. Again, the assembly is designed to deter tampering, though this time it is with Torx screws, and tabs that lock the side panels.

Unlike SMART-PANEL, DIATEC’s recesses are not merely confined to the front. One edge is also recessed to help protect connectors and interfaces. This useful feature is also evident (though more pronounced) on NET-BOX (IP 65) which conceals connectors beneath a removeable front lid. Optional infill covers close this underside opening to create more space for PCBs or assemblies.

Enclosures like NET-BOX are designed for network nodes, gateways, data acquisition and central control units. Aesthetics come to the fore with its slim profile, curved top and the concealment of its anti-tamper Torx assembly screws. NET-BOX can also be specified for desktop duties by adding non-slip feet (accessory).

Surprisingly, there have been few standard wall-mount enclosures designed to fit an internal corner. One such is SMART-CONTROL (IP 55), a wedge-shaped ASA+PC housing that is at home in 90° corners or on flat walls. Like NET-BOX, it can also be used for desktop electronics (by specifying an optional stand set).

However, IIoT’s industrial settings sometimes call for more rugged enclosures that can cope with challenging conditions. Look for housings with impact ratings of IK 07 or IK 08 and ingress protection of IP 66 (temporary flooding) or IP 67 (shallow immersion). IK 07 (2 joules) is equivalent to dropping a 0.5 kg mass from a height of 400 mm, whereas IK 08 (5 joules) is the equivalent of 1.7 kg mass dropped from 300 mm.

This is territory for industrial electronic enclosures such as SOLID-BOX (IK 08, IP 66/IP 67) and IN-BOX (IK 07 ABS, IK 08 PC, IP 66, IP 67). IN-BOX can be wall mounted either directly or with brackets (accessory). By fitting these brackets to the enclosure first, you can install IN-BOX lid closed, protecting the electronics in dusty or wet conditions. SOLID-BOX also offers ‘lid closed’ installation with separate channels for the concealed lid and mounting screws.

Most enclosures will require customisation, usually machining and printing. Other services include lacquering, decor foils, laser marking, special materials, EMC shielding, and installation/assembly of accessories.

ROLEC OKW Australia New Zealand Pty Ltd Managing Director Shane Dwight said: “It takes surprisingly little customisation to transform a standard enclosure into a unique housing ideally suited to a specific application. Sometimes it can be as little as some machining and the addition of a touch screen display or a membrane keypad.”

For more information, view the OKW website: https://www.okw.com.au/en/Products/IIoT-sensor-enclosures.htm.