COMPONENT DESIGN
Passing the stress test D
Reliable electronics should always be designed with safety in mind
esigning a highly reliable electronic component can depend on various factors. This includes whether it is used to a full rating or including a safety margin, as well as the device it has been designed for and its environment. Here, Tadek Dzwig, research and development manager at remote monitoring specialist Omniflex, explains what to consider when designing reliable electronic components for remote monitoring applications.
To make a component highly reliable, it depends if you use it to a full rating or with a safety margin. In electronics, it is important we give ourselves a safety margin. It is well-known that using an electronic up to 50 percent of its specified rating makes it more reliable than running at 100 percent.
Indeed, some components are infallible at a light rating. This is particularly applicable to passive components. Reliability figures for active components must be gathered at source. There are, however, safety margins for temperature; components that run at 40 degrees are more reliable than those running 60. Referring to recognised data tables such as those provided by Bellcore/Telcordia can aid manufacturers in gauging reliability.
Designing with reliability in mind The safety margin must be established at the outset. Any calculation of reliability generally includes the stress factor and quality factor; these are the multipliers when calculating reliability. Having a stress factor of over 50 percent is likely to lead to reduced reliability. Quality factors involve controlling the source and supply of components. ISO 9000 standards strictly control these methods, as only components that are listed for purchasing
are using the safety standards that can be provided, demonstrating a good quality factor. Also, it is important that when repeating manufacture of devices that the same result is achieved using the same materials and components, ensuring that any doubts about a component’s reliability is reduced. Several design considerations depend on the environment the electronic is operating in. Environments such as power stations, explosion areas or chemical plants, or high vibration areas like ships and trucks call for the utmost reliability.
For example, if an electronic component is mounted on a ship’s engine, we need to know if it can survive the continuous vibration environment. In explosion areas, qualified reliability and special calculations are required as anything can be a source of ignition, either by spark or heat. If there is a mismatch from
the type of gases present with electrical energy from a potential fault, a dangerous situation materialises, including explosion.
With electronic design, it is important to have yearly proof testing and build in obsolescence, outlining a typical period when a part may need replacing, to guard against any safety concerns.
Remote monitoring
Remote monitoring devices have a strong safety element to them. Whether that is monitoring for leaks in a pipeline, temperature monitoring of medical samples in cold chain or monitoring mooring lines for ships in a harbour, each one has a knock-on effect for safety. All the scenarios need reliability to require experts to act. These are monitored because there is a degree of risk attached to the process and want to be notified, so the electronics need to be reliable, and they can trust any information that is received. Simplicity can also be used to reduce any variables to make safety calculations easier. There is, however, room for design for more complex components. For example, if there is failure, one needs to ensure that in certain scenarios that any component failure trigger a device to fail into a safe state. This can take the form of access control which denies access to personnel if their safety can be compromised in any way, whether the area in question is unsafe or the device is unable to report a safe area. Building in diagnostics into the units can recognise if there is a device failure.
14 OCTOBER 2024 | ELECTRONICS FOR ENGINEERS
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