surrounding possibly dangerous segments of equipment with: n Sheet-metal housings and chain-link or glass fencing n Sliding glass panels, doors, and swinging gates n Sensors and light curtains n Specialty barrier components of other electronic or physical design n Safety interlocks — the focus of this article
switches, interlocks are those that are triggered through the movement of either movable machine or perimeter sections. To be clear though, safety interlocks can be triggered by actuated perimeter sections or those that are manually opened. Their name derives from the way they inter-lock (and render interdependent) allowed safety- controller conditions and perimeter- gate positions … whether open or closed or something else. In other words, interlocks provide feedback to safety controllers that in turn elicit the correct machine status for a given set of machine-guard positions. Standards governing the inclusion of interlocks Currently, the design and integration of interlocks of industrial-automation applications must satisfy five full standards — including Conformitè Europëenne (CE) Machinery Directive 2006/42/ EC. ISO 12100 (and adopted ISO 14119 passages) define interlocks as devices that prevent hazardous machine operations when gates into the guarded area are open. The interlocks called guard locks or locking gate switches that go a step further to latch gates closed are subject to their own requirements — including the requirement that they feature an escape latch for technicians who find themselves locked inside a dangerous work cell.
way to categorize these safety components is to group them by whether machine operator or other plant personnel make direct physical contact with that safety component (as with light curtains, for example) or whether some intermediate machine subsection contacts the component. The latter include an array of machine- activated safety switches and sensors as well as interlocks. So, what exactly are interlocks? They are mechanical, electrical, or electromechanical safety components that are at their core a proximity or position switch. They always install on machine confines at moveable (penetrable) gates. Unlike safety curtains or operator
Though guarded machine perimeters mostly consist of
immovable elements, the movable or penetrable sections mentioned (including window shields, curtains, and doors) can allow operator access at strategic locations for machine tending, adjusting, or servicing. A convenient
Figure 1: On each of this machine’s doors, limit switches verify closure before allowing the machine to startup. (Image source: Getty Images)
Basics of safety interlocks
Written by: By Lisa Eitel
are well-defined boundaries around the machine — and safeguarding or machine-guarding components. Though safeguarding is a term casually used in some literature, standards from the International Organization for Standardization (ISO) and an increasing number of automation component suppliers assign it a very specific definition. These authoritative industry sources generally limit guarding to mean components and subsystems
Keeping plant personnel safe requires that they be protected from mechanical threats to bodily harm. This field of safety engineering is called industrial risk reduction. Local laws and industry standards legally require that automated equipment include various mechanical safety features to prevent dangerous machine startups and trigger safe shutdowns should a new risk of personnel harm arise. The foundation of these safety systems
Contributed By DigiKey's North American Editors
we get technical
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