Rugged Electronic Components for Tough Industrial Applications
Live Electronics
We are the leading UK specialist supplier of electronic and electrical components and products for demanding industrial
A World Built on Electronic Components
Our world as we know it would not function without electronic components. They are vital for almost everything we do: at home, at work and in our leisure hours. They underpin the systems that we need to survive, communicate, explore and develop as a society, from education and healthcare, to manufacturing, finance and energy.
Modern electronic components are often highly sophisticated devices; for example, even something as straightforward as a humble connector will make use of extremely advanced materials and electrical interfaces to optimise the speed and integrity of signal processing.
As our world expands and the technologies we employ become ever more complex, so our demands on each generation of electronic components grow. In particular, we expect electronic products and systems to operate safely and reliably under ever tougher environmental conditions. These include the depths of the oceans and the extremities of space, but can be as ubiquitous as a warehouse, manufacturing site or engineering workshop. In each case, the effectiveness of every system is determined by the functionality, durability and performance of rugged electronic components.
What do we mean by rugged components?
In simple terms, rugged components are designed for use in tough, harsh or hazardous operating environments. These environments are often specified in industrial standards, such as the NEMA (National Electrical Manufacturers Association) ratings or the IP (Ingress Protection) code described in IEC 60529. More broadly, they are normally taken to include environmental conditions (temperature, pressure and humidity), the mechanical environment (vibration or shock) and the electrical environment (noise and potential for electromagnetic interference). ?
It’s worth noting, however, that there is no official definition of a rugged component. Instead, different industries and applications have their own accepted criteria for what is considered rugged. In practice, this means that a component has to be fit for purpose, which is determined by the application or operating conditions. These typically include:
The more obvious examples of harsh operating environments can be found in deep-sea oil and gas exploration, where electronic components have to function remotely at progressively higher pressures and temperatures, frequently with potential exposure to aggressive gasses and fluids. By comparison, a manufacturing line may not instantly suggest a particularly hostile operating environment yet dig beneath the often pristine surface and you’ll quickly find electronic devices that are exposed to similar levels of environmental stress. Typically, this will include high and intermittent levels of shock and vibration but can also include extreme temperatures and exposure to particulates, moisture and corrosive gasses.
Designing Rugged Electronic Components
Rugged electronic components are normally designed with specific principles in mind, to ensure their reliability and resilience. As noted above, the primary design considerations include mechanical durability, environmental protection, temperature tolerance and electromagnetic protection.
Mechanical durability and vibration
Mechanical durability essentially depends on the materials used to construct the component, to provide mechanical strength and, in terms of its outer case or enclosure, to protect it against external damage. Electronic components are normally manufactured from plastics, metal or a combination of the two.
Components produced in high volumes are generally injection moulded using polycarbonate (PC), acrylonitrile butadiene styrene (ABS) or polyethylene terephthalate (PET) to provide impact resistance, with elastomeric polymers sometimes being added to improve durability. Polycarbonate blends are widely used for low voltage components such as switches and connectors, as their high mechanical strength, flame retardancy and heat resistance combine with in-mould viscosity and flow characteristics, which allow greater design freedom to give, for example, thin and clearly defined wall shapes.
Correct choice of material is also important for electrical contacts. These need to provide optimal signal transmission, while being sufficiently robust to resist vibration and, in some applications, wear that arises from repeated mating cycles. Standard metals include brass and beryllium copper, with the latter providing the best combination of mechanical and electrical properties.
For switch and relay contacts, where circuits are continuously made and broken, it is common practice to plate contacts with a thin layer of platinum, palladium, gold, silver or silver alloys, such as a silver-tungsten mix. This improves the electrical properties, reduces the effects of arcing and enhances resistance to wear, oxidisation and corrosion.
Gold is more conductive than silver and is normally chosen for connector terminals or contacts where low electrical resistance is critical and where arcing is unlikely to occur – arcing causes the gold to vaporise. In general terms, gold is preferred in circuits where power is below 0.4VA, or 20mA at 20VDC, or 100mA at 4VDC. Beyond this, silver is normally chosen.
One of the challenges of using silver instead of gold contacts in switches operating at low currents and voltages is that oxidation on the surface of the contact can interrupt the switching currents, causing intermittent failure.
A further consideration is the contact shape, as this needs to provide the best possible electrical contact area, yet be free of stress points that may fail through repeated mating cycles or extended vibration.
Vibration can be a particular problem with industrial equipment, whether this be a machine tool such as a press-brake or CNC mill that is fixed in place, or a piece of mobile or off-highway equipment. In each case, vibration is caused by a combination of acceleration, velocity and displacement within the operating environment. This can cause mechanical and soldered connections to fracture, component parts to become misaligned, intermittent signals from pin connections, or fretting, where wear occurs between loaded contact surfaces.
The solution can be to use flexible terminations, which allow sufficient free movement to absorb vibrational movement, to fit anti-vibration plates, or to protect the device as whole by using isolators or dampers. Additionally, there is a wide range of connection devices that feature anti-vibration or locking mechanisms – these are often ideal for use in applications such as robotic systems where excessive flexing presents a risk of cable pull-out.
Ingress protection
One of most common requirements for electrical components is the need to protect them against the ingress of particles and moisture. Ingress protection (IP) is defined in the international standard IEC 60529 – IEC is short for International Electrotechnical Commission.
An IP rating contains two numbers, indicating the level of protection against solid objects and water. For example, a rating of IP67 indicates that the component is protected against the ingress of all solid objects up to and including light dust, and can be temporarily immersed in water. Please refer to the graphic to see the full classification.
Note that occasionally an extra letter may be added. This is generally to indicate that the component has also been tested against particular materials or hazards, such as oil or high voltage, or show the conditions under which the tests took place, for example, in moving water. Also, if a rating is shown with an ‘X’ – e.g. X6 or 5X – it indicates that the component has only been tested for particular or moisture ingress, but not both.
Ingress protection normally applies to the device enclosure and any parts that form an interface between the internal and external states; i.e. connectors, switches or indicators. IP ratings can also be applied to printed circuit boards or other parts that have been conformally coated to seal the board components.
Components at the interface between internal and external environments typically use cable glands and rubber seals, or silicone sealing materials, to prevent the ingress of particles or moisture. Further options include potting, where the internal electronics are encased in an epoxy resin, or over-moulding of either individual components or, indeed, the entire device.
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A similar approach is also taken if electronic devices need to have gas-tight or explosion-proof connections where, for example, screw-threaded or bayonet coupling mechanisms, or specialised glass-to-metal or ceramic-to-metal insulators are used to provide optimal protection.
Temperature and flame resistance
Providing resistance to extremes of temperature – at both ends of the temperature spectrum – is generally achieved by the choice of material and the method of construction. Two of the greatest challenges are the effects of expansion and contraction, which can cause connector pin contacts to loosen, and the affect that high and low temperatures have on material properties.
High temperatures above +150°C, for example, can cause plastics that exceed their glass transition point to weaken and distort; at the opposite extreme, sustained cold below -55°C will result in plastics become brittle and cracking, allowing moisture or particles to penetrate the device. The solution is to choose components manufactured either from specialised plastics with appropriate properties or, in particular circumstances, to metal parts.
Materials used in electronic components will need to comply with fire standards such as ISO 834- 1, or be manufactured from flame resistant low-smoke-zero-halogen (LSZH) plastics that meet the requirements of UL94V-0. LSZH compounds are widely used for cables and connectors in poorly ventilated areas as, unlike traditional polyvinyl chloride (PVC), polyethylene (PE) or thermoplastic urethane (TPU), they will not release toxic hydrogen chloride gas in the event of a fire; this gas can react with water to form hydrochloric acid.
hazardous areas, where the presence of gasses, dust or petroleum products create the risk of explosion, it is essential that electronic components are designed and manufactured to minimise or eliminate the potential for an electrical spark or arc and to prevent a rise in the surface temperature of the part.
These intrinsically safe devices must comply with the requirements of the UL, ATEX or IECEx standards, which categorise hazardous areas based on the degree of risk from the materials present. For example, UL913 defines three areas:
ATEX and IECEx take a similar approach, with ATEX defining two main types of hazardous zone, each of which is subdivided by the type of gas, vapour or dust present. Additionally, ATEX specifies three groups of equipment, defined by where they can be used.
Electronic components that are certified for use in hazardous areas typically use low voltage circuits, to minimise the electrical energy potential, intrinsically safe fuses, seals and cable glands to isolate the device from the surrounding atmosphere, resin encapsulation of arc-producing elements, or explosion proof enclosures.
Electromagnetic interference
Electromagnetic interference (EMI) is created by energy waves with different frequencies generated by the acceleration of electrons in electrical circuits. EMI can originate from devices such as radio transmitters, mobile phones, electric motors and power cables, as well as naturally occurring lightning and solar magnetic storms; depending on the source, EMI can be continuous, pulsating or sporadic.
Electromagnetic energy generated by one source has the potential to interfere with the operation of any unprotected electronic device in the immediate vicinity. Typically, this might be the interruption of a switching sequence in a digital circuit that causes control or monitoring signals to be corrupted, resulting in intermittent faults or a complete system malfunction. If the system is safety-critical then the implications of a failure could be severe.
The effects of EMI can be addressed both by reducing its potential within the source device and by protecting electronic equipment from external interference. In practice, electronic devices are generally designed to address both aspects of EMI; this methodology is commonly referred to as EMC or electromagnetic compatibility.
There are various international and national EMC standards, which govern the design, operation and testing of electronic devices. Some of these standards are generic, while others such as MIL-STD and IEC 60601 are sector specific – military and medical in the examples quoted.
The effects of EMI are generally controlled by the use of shielding around the emitting device or within the overall product enclosure. Shielding can take the form of a solid metal cover, wire mesh with the openings matched to the wavelength of the emissions, or the use of silicone-metal paint within the enclosure.
Devices where enclosures need to have openings for cables or displays can present particular problems as each opening effectively leaves a gap in the shielding. The solution is to use filtered connectors, such as a filtered D-sub; these incorporate low-pass filters to allow low-frequency currents and signals to be transmitted without degradation, while attenuating the high-frequency EMI wavelengths.
For best results, work with the experts
Choosing the correct rugged electronic components can be complex. As we have indicated in this document, there are many variables in terms of both component specification and regulatory compliance, all of which need to be given careful consideration.
This is where working with an expert supplier of rugged electronic components is crucial. At Live Electronics, we’ve years of experience working with customers across many different industries, from manufacturing to defence and automotive, so we understand the challenges of product design, development and component selection. We also have strong relationships with leading component manufacturers from around the world, giving us access to their in-house technical expertise and, in some cases, to specialised custom engineering facilities.
As a small, dedicated team we have the skills, experience and resources to help you define your component requirements, with all the information and technical knowledge that you need to develop electronic devices that are safe, functional and capable of performing under the most demanding environmental conditions.?
If you'd like to learn more please contact us:
Live Electronics, Unit 1 Saxon Terrace, Gallamore Lane Ind Est, Market Rasen, LN8 3HA.
Tel: 01522 217555
Email: [email protected]