June 2014 Newsletter

Safety Light Curtains

Safety Light Curtains play a vital role in keeping manufacturing workers safe.  They provide a viable option to hard-guarding with safety interlock switches or safety mats.  This month’s newsletter will cover the basics of light curtains.  Principle of Operation:  A light curtain consists of a transmitter, receiver, and a safety relay.  The transmitter and receiver are optically ‘connected’.  A series of light beams are transmitted to the receiver.  When an object interrupts the beams, a signal is sent from the receiver to the safety relay. Resolution: Typical resolutions are 14 mm and 30 mm.  Resolution is the spacing between the beams and determines the size of the object required to interrupt a single beam.  To signal for the typical human finger, a 14 mm resolution light curtain is required.  For a hand or ankle, a 30 mm resolution is required.  The height of the unit is determined by the height of the opening to be guarded.  Heights can be in the approximate range of 10” to 100”.  Modes of Operation: Two primary modes of operation are available.  The first one requires a reset of the safety relay after the interruption has cleared.  This would be similar to pressing the reset after an E-stop PB is released or the safety switch on a guard door is made.  The other mode is for ‘pause’ and resets automatically after the interruption has cleared.  In this case, the signal from the relay could be an input to a PLC and used in the logic to temporarily pause the machine cycle – maybe to allow for load/unload of parts during machine dwell.  Applications:Multiple sides of machines can be guarded using mirrors and a single transmitter/receiver pair.  Multiple levels can be guarded by cascading pairs in a step-type arrangement.  Maintenance:  Some very simple planned maintenance of light curtain systems can eliminate nuisance interruptions in the future.  Periodically check to make sure that the mounting brackets for the transmitter and receiver pair are secure.  This will help prevent the pairs from getting out of alignment from vibration or physical contact.  Pairs that get out of alignment act the same as an interruption of the light beams.  Depending on dirt in the immediate environment, occasionally wipe off the pairs with a clean cloth and minimal pressure.  Finally, routinely interrupt the light beams while the machine is in a dry-run mode and verify that the response is as designed. 

Electrical Safety in the Workplace

This is a continuation in a series of snippets on NFPA 70E.  This one concerns Article 130.2 Part (A) – working on energized circuits.  It defines three exceptions that allow for work to be performed on energized circuits.  First, ‘de-energizing introduces additional hazards or increased risk’.  Second, it ‘is infeasible in a de-energized state due to equipment design or operational limits’. Lastly, circuits operating ‘at less than 50 volts’ can be worked on while energized.   Notice that there is no exception due to economic factors, since the Standard places the highest value on human life and well-being.  It is important to note that testing or analysis is allowed on energized circuits when following safe work practices and wearing proper PPE (personal protective equipment).  Finally, Part (B) describes the requirements for an ‘Energized Electrical Work Permit’ to be completed and approved for energized work. 

Safety Training Available

In addition to our normal controls work, Wortman Controls Inc. is now providing training on Electrical Safety in the Workplace to local companies.  Whether you are just getting started with the implementation of NFPA 70E, training new employees, or refreshing your current employees; you will find our rates reasonable and without the added travel expense (as we will do the training at your sit