Wednesday 2 March 2011

Wireless Sensor Networks and Safety

Not quite the sexiest of topics, but an interesting one nonetheless. My work finds me at current designing and architecting conventional albeit highly reliable and fail-safe (literal failure of anything results in electrical and physical isolation/safety states) cabled systems. A combination of both electrical and pneumatic actuation, coupled with two and three wire sensors.

A feature of all these systems, as hinted at, is the necessity of safe failing design. To ensure that the failure of a sensor, cable, relay, contactor or controller results in a safety state, rather than a potentially lethal state. A prime example, is to energise-to-run, and close-to-permit. Translating this to wireless sensors and actuators proves a little more challenging.

My underlying concern is always with a software failure within the wireless stack or within the gateway controller. With most wireless being ZigBee based, at some point a software stack that's less than bullet-proof will be involved with processing the data.

Yes, everything has a mode of failure. It's a given. But some things have significantly high numbers of modes of failure. Anything with code is a prime example of the latter. So, rule one would be to reduce the criticality of the modes of failure - prepare for the worst, so ensure the modes of failure give you an appropriate feedback, rather than false feedback.

I'll expand more on safe design a little later, but this really just scratches the surface and introduces Wireless I/O for some interesting projects to come...

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