Design World July 2015

Page 73

M o t i o n

C o n t r o l

Just like the mysteries surrounding Stonehenge, crop circles, who shot JFK, and what a self-respecting individual would actually do for a Klondike bar, some motion-control considerations cause significant consternation, confusion and debate. No application engineer really wants to deal with these grey areas of motion, but most are eventually forced to do so during one design or another. The most heavily debated topics include closed loop versus open loop versus hybrid technology; sinking versus sourcing I/O; and the load to rotor inertia ratio. Another grey area is the meaning of IP ratings for industrial motors and how they relate to specific applications.

To dispel some of this confusion, let’s define IP65-rated components and what they do and don’t mean for applications. That will give us an understanding of how to correctly apply these components.

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IP ratings: the true letter of the law Ranging opinions about the meaning of IP ratings is frustrating, but actual definitions are very specific. Published by the International Electrotechnical Commission (IEC) and detailed by IEC standard 60529, IP ratings—also known as Ingress Protection ratings or International Protection markings— rate the protection components provided by mechanical casings and electrical enclosures against intrusion (including body parts such as hands and fingers), dust, accidental contact and water. In other words, an IP rating indicates how well the enclosure of a device shields internal subcomponents. The ratings include two or sometimes three numbers.

IP number First position Second position Third position

Indicates protection from … Solid objects or materials Liquids (water) Mechanical impact (commonly omitted as not part of IEC 60529)

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July 2015



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