Monday, April 21, 2014

Presence Sensing Equipment


When working through the hierarchy of controls, one of the common engineered controls is presence sensing.  These are devices that are meant to detect the operator before they reach the hazard.  They are more flexible than fixed guarding because they allow the operator to interact with equipment until they reach a predetermined hazard zone. It’s important to note that unlike barrier guards and two hand controls, they don’t prevent access to the hazard zone, they prevent dangerous motion when inside the hazard zone. Some of the more common presence sensing devices are safety mats, light curtains, and laser scanners. 

 safety mat light curtain  safety laser scanner

There are many other devices that can be used to detect operators.  There are many considerations before installing these devices, but here are some of the first questions you should ask:

1.       Usage: Make sure that the device you are installing works with the equipment you are installing it on.  A light curtain requires a machine to be able to stop at any point in its cycle.  Also presence sensing does not protect against flying objects.  If items are ejected accidentally out of the equipment, these devices will not provide protection.

2.       Resolution of device:  This relates to what level of detection the device provides.  For a light curtain, the resolution outlines the amount and spacing of the beams.  Light curtains can come with the ability to detect fingers, or only detect body. Devices that are located closer to the hazard zone need the ability to detect smaller objects that reach into them (like fingers).

3.       Safe Distance: Once a device has been selected, is it mounted or installed at a safe distance to prevent access to the hazard by the operator.  Safe Distance is a calculation based on the speed of movement of the operator into the hazard zone and the stopping time of the machine (including the safety control system).  It’s important that operators when entering the hazard zone cannot reach danger before all hazardous motion has stopped.

4.       Performance Level: What performance level is the installed safety device?  Is it control reliable, meaning that redundancy has been built in to ensure that if problems occur with the safety control system, that the machine will not function?


These are some of the first questions that you may ask, but the CSA Standards outline many more design and performance criteria that you need to consider before installing a presence sensing device.  If you are installing a device, or have one currently in place, don’t hesitate to call us with any questions you may have.

Posted by Kristin Petaski at 12:06 PM 0 Comments
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