Issue link: https://read.dmtmag.com/i/530880
54 • JULY 2015 • WORLD FENCE NEWS Visit Logical Decisions at www.ldi.com Your Gate Operator Specialist Find us on A note regarding UL monitored external entrapment protection device protocols The following open letter to the industry was submitted to World Fence News by Carsten Idland of the consulting engineering firm ASE Industries of Mar Vista, Calif., which provides engineering services to the gate operator industry. It is intended for educational purposes to clarify an issue pertain- ing to monitoring protocols, which will be part of revised UL 325 standards which become effective in January 2016. UL has left open which protocol can be used with the monitored external entrapment protection device required in January of 2016. This has led to a number of different concepts for monitoring which have been developed by manufacturers. One method is to use different frequencies to give the status of the sensor. One frequency is used to indicate a functioning unobstructed sensor. Another frequency is used to indicate when an obstruction is present. No frequency indicates a missing or defective sensor. Another method being used is based on current output of the sensor for status. The level of current indicates the status of the sensor. An obvious way to accomplish monitoring is to use a sensor of standard configuration and control the power going to the sensor. A typical photo sen- sor configuration has a two wire power supply and three wires going to a SPDT relay. The relay has three wires connected to it which connect to the various contacts Normally Open (NO), Normally Closed (NC) and Common (C). Typically, when the photo sensor is powered, the beam is correctly aligned and is not obstructed, the NC contact is connected with C. Testing the presence (monitoring) of the photo sensor can be accomplished by first having the control board test that the sensor is in a proper state, i.e., NC con- nected to C. Next the control board removes power to the sensor and verifies that the NC contact is no longer connected to C. An enhanced approach would be to also monitor the connection between NO and C. All the techniques above require that the control board have additional circuitry to perform the monitoring function of the sensor. One of the advan- tages of the power control protocol is that no added circuitry is required on the sensor as compared to presently used sensors. Carsten Idland ASE Industries Mar Vista, California Classics from the late, great Rodney Dangerfield • My wife's jealousy is getting ridiculous. The other day she looked at my calendar and wanted to know who May was. • My wife met me at the door the other night in a sexy negligee. Unfortu- nately, she was just getting home. • I told my psychiatrist that everyone hates me. He said I was being ridiculous – everyone hasn't met me yet. • I was so ugly my mother used to feed me with a slingshot. • The way my luck is running, if I was a politician I would be honest. • When I was a kid my parents moved a lot, but I always found them. • My psychiatrist told me I was cra- zy and I said I wanted a second opinion. He said okay, you're ugly too. • I haven't spoken to my wife in years. I didn't want to interrupt her. • I could tell my parents hated me. My bath toys were a toaster and a radio. www.rhinotool.com info@rhinotool.com 866-707-1808 Pushing the Boundaries Multi-Pro ™ Gas Powered Driver Powerful Pro-Series Gas Powered Drivers and Air Operated Post Drivers from Rhino Tool Company Our latest technology with ease of transport and plenty of power to take on a wide range of fencing projects. Visit our website to locate a dealer near you! Fence Pro™ Gas Powered Driver PD 55 Air Operated Post Driver Manufacturing Quality Post Drivers and Post Pullers in the USA Since 1977