Reversing Devices have the purpose of helping the operator detect an obstruction, while closing. This will then cause operator to reverse, into upward direction, until full open position.
Basically, a “normally open” switch is activated, thereby closing the reverse circuit of the electric operator’s open contactor. Some operators offer the feature of a time delay, before abruptly reversing the momentum of a traveling door. This can even be an upgradeable option.
A Photo Eye is an approach typically used with residential operators, as well as commercial. Residential Trolley Operators are also required to have the operator unit itself sense unusual resistance, and reverse the door. Most residential operators use an emitter/receiver style photo eye. One optical unit transmits, while the other receives. If the transmit path is broken, while the operator is in between the open, and close, position, a circuit will close, and the operator will open the door. Other industrial style Photo Eye units are also available. These ones can emit/receive, or transmit/reflect. These boxed units offer mount to a sturdy bracket. They can be less susceptible to outdoor environments, keenly, less affected by interference from the sun.
A Safety Edge can be attached to the bottom of a door, along the entire width. If the door closes on an object, the safety edge should detect it, and activate the reverse circuit. A Pneumatic Safety Edge uses a gum hose, and air switch, to detect obstructions. An Electrical Safety Edge can use two lengths of conductors, separated by a segmented foam, to open, and close, a circuit. A Safety Edge will often take use of a take up reel, or a curly cord, to communicate to the operator. The signal can also be transmitted by remote. The transmitter can be attached to the bottom of the door, and powered by a 9 volt battery.
When redundant devices are used, a cord for the Safety Edge can cross the path of the photo eye during normal door travel. Adjustable sensitivity of some available photo eyes can allow the cord to pass, while still serving it’s purpose; detecting unwanted obstructions.
Gate operators often use vehicle loop detectors as a means of sensing obstruction. They can also incorporate use of photo eyes and safety edges.
Nothing is fool proof. Obstructions may not always be caught within the zone of the detecting device(s). One consideration, for all safety devices, is the amount of “downward coast” that still occurs before the door actually reverses. This can be affected by variables, such as, the means of braking, the weight of the door (after being calibrated for spring balance, how much force is still applied to the operator), the condition of the door, or, the condition of the devices themselves. An electric operator can be wired “constant pressure to close”, so that someone must physically hold the close button while the door is shutting. This encourages monitoring for obstructions during the close cycle of the door.
Doorsmith, Inc. is a commercial repair, and installation, service that proudly serves Orange County, California. We are available for inspection, maintenance, and repair of all types of commercial doors, gates, and dock levelers.
Please contact us at 1 800 315 6839.
www.http://DoorsmithInc.com
CA License 902488
