EMC Regulatory Compliance does not ensure functional safety
12 May 2017
One of the biggest problems faced by all electrical and electronic equipment is that of electromagnetic interference (EMI). However, what's peculiar is that, despite the rising use of devices that are susceptible to EMI, until recently there have been no clear guidelines for EMC as regards functional safety. Here, Keith Armstrong, worldwide EMC specialist at EMC Standards, looks at how engineers can ensure that EMI will not cause excessive functional safety risks.
All electrical and electronic technologies emit electromagnetic (EM) disturbances that can interfere with the correct operation of radio-communication equipment or other electronics. Modern technologies are particularly likely to cause such disturbances, worsening the EM environment that electronic devices are exposed to.
EM disturbances can cause problems to electronic equipment, ranging from degraded functionality to complete failure. The discipline of controlling the limits of EM emissions and the levels of immunity is known as electromagnetic compatibility (EMC).
EMC is increasingly becoming more valuable in electrical and electronic engineering. As we continue to integrate more electronic technology into our lives and into our businesses, from computers and mobile phones to variable speed drives (VSDs) and programmable logic controllers (PLCs), we are also seeing a rapid increase in the use of electronics in safety-related applications.
Engineers and their managers are all under pressure to make sure that the equipment and systems we use in our businesses do not expose people to safety risks. Despite the fact that most of us understand the importance of protecting devices against electromagnetic interference (EMI), there is often confusion about exactly what constitutes good EMC in the interest of ensuring that EMI does not cause excessive functional safety risks.
Good EMC vs EMC compliant
Many people think that the one necessity for good EMC is that equipment and systems meet the EMC Directive and are CE-marked. Unfortunately, neither the EMC Directive nor its harmonised EMC standards cover EMC-related functional safety, and this is clearly stated in the EMC Directive.
Also, most of the safety standards that are harmonised under the Low Voltage Directive do not cover EMC-related functional safety and some do not even cover functional safety at all. The Machinery Safety Directive and its harmonised safety standards attempt to cover the EMC issues for machine safety; however, they eventually fail by referencing the EMC Directive and its standards, which do not cover safety issues.
Because of the lack of coverage of this increasingly important issue by existing EMC or safety standards, issues of EMC-related safety are falling short of a sufficient solution. Since the commercial pressures on manufacturers are such that they are unwilling to go further than what they perceive, often incorrectly, as being their minimum legal obligations, the resulting safety risks are uncontrolled.
Although some IEC standards and technical reports have subsequently addressed these issues, they are not yet widely used or understood. They are also not explicitly harmonised under any EU Directives and unlikely to be so for many years yet.
EM in effect
As an example of an increasingly common EM disturbance, consider the possible proximity of mobile radio-communications to a safety-related electronic system. The EMC Directive’s immunity standards require normal functional performance to be maintained when exposed to radio-frequency (RF) fields at either three volts per metre (V/m) for residential, commercial and light industrial environments; or ten V/m for normal industrial environments. However, what do these V/m levels mean in real life for the proximity of mobile radio-communications?
Let us imagine that an engineer is using a mobile phone in a residential area with poor reception. If this were to have two watts of RF power, then we might expect any safety-related electronic systems in the area to maintain functional performance if the engineer was between roughly 2.5m and 5m from the system. In a normal industrial environment, however, it would be necessary to maintain functionality between 0.8m and 1.6m.
In this situation, if the engineer operated a connected PLC while using his mobile phone, he would obviously be much closer than 0.8m so the field strengths could exceed 10V/m and the equipment could suffer from degraded functionality. This could range from false data, such as bypassing a limit switch, to total failure of the operating system.
To ensure functional safety from an EMC perspective, it is critical that engineers carry out an effective hazard and risk assessment. This should consider what EM disturbances the apparatus may be exposed to; how the equipment’s own EM emissions impact other devices; what the health and safety implications of a disturbance are; and the confidence that the design will not permit EMI to cause excessive safety risks over the entire lifecycle.
EMI is set to be one of the biggest challenges that engineers will face in the future as more devices come into widespread use and confusion over functional safety persists. While the IET’s 2013 guidance will be published in early 2017 as their important new Code of Practice on “Electromagnetic Resilience in support of functional safety”, engineers should not delay in learning more about this important issue.
Information about EMC and the IET’s 2013 guidance can be accessed from the EMC/EMI risk management section of the EMC Standards website, alongside many helpful and informative articles and presentations. It is only by following the IET’s 2013 guidance (or modern guidance developed from it, such as the IET’s new Code of Practice) that engineers can ensure that equipment and systems are functionally safe as regards EMI.
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