Machine Safety - Cableless vs Wireless
Machine Safety and “cableless” vs “wireless” has been an ongoing discussion over the past two years as this technology rapidly travels through its evolution cycles to the plant floor. Personally, I’ve sat in a dozen discussions over these two terms and how to choose a word that best describes the application as well as the issues. To wrestle this one to the ground it’s my recommendation that we choose an application like - cableless pendant control. Now, let’s discuss these two terms and which one best fits the application.
The application is a hand held pendant operator station which means it functions like an operator station and it’s portable. Since it is portable and cableless that means that it has its own power supply and that the communication signals for control are not cabled back to a panel. Therefore, the communication signals are wireless. If this particular pendant operator station also includes safety functions like emergency stop then the safety-related communication signals are likewise wireless. So, is this particular application and device “cableless” or “wireless”?
In my opinion the answer is “cableless”! The reason is that wireless in this case is a more generic term and it only describes the type of control communication technology. Being generic, this term can also apply to wireless - sensors, controllers, monitors, switches, etc. which can all be rigidly mounted and cabled for power. Since a cableless operator control station also includes its own power supply (like a battery), there are no cables for power or control. Therefore, this application in my opinion should be considered a “cableless” application which sometimes can also have safety-related functions. This understanding is critical to the safety standards community because it directly impacts the application requirements that must be addressed by the standard.
Some of the application issues include; audible and/or visual signs to show active status, possible out of sight storage when not in use, zone control (yes or no), what happens if there’s a loss of signal or power, can the panel stay active if a docking station is provided, to mention a few. Many of these application issues do not need to be addressed if the application is only wireless and not portable. I advise that a thorough risk analysis of your application issues is essential in considering this technology around your machine.
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Posted by J.B. Titus on March 15, 2010
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