UL Monitored Photo Eye Technologies

Effective January 12, 2016, UL 325 safety standards required that all safety devices installed on gates must be monitored. Monitored photo eyes are an effective way to keep your automatic gate system in compliance with this safety regulation. There are currently four types of monitored photo eyes on the market.

Normally Closed

With normally closed photo eyes, the photo eye closes the circuit when the beam is not obstructed. Before each open cycle, the gate operator must cut the power to the photo eye transit side to ensure that the circuit opens and closes again when power is reapplied. This technology is typically used with through-beam photo eyes.

Normally Open

As the name suggests, the normally open photo eye is just the opposite of what a normally closed photo eye is. In this model type, the photo eye is open when there is no obstruction to the beam. Then, when an obstruction is sensed, the photo eye will remain closed.

Pulsed

2-wire and 4-wire pulsed photo eyes use a pulsed "heartbeat" over the power connection when the beam is obstructed. The photo eye will stop sending the pulsed updates when it fails or is obstructed.

10k Resistive

When the photo eye beam is obstructed, a resistance of 10k is applied. The board is able to measure this. The resistance is removed when the beam is clear again.