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Photo Eyes and Edge Sensors for Gates

By carlsbad metal gates record

Two sensors, two different jobs

Photo eyes and edge sensors are the pair most often found on automatic driveway gates, and they are frequently confused. Both stop a moving gate. They work in opposite ways. A photo eye notices an obstruction before the gate touches it, by watching a beam of light. An edge sensor notices an obstruction after contact, by feeling pressure on a strip along the leaf. Knowing which does what makes it easier to place them, test them and diagnose a gate that refuses to close.

The photo eye in detail

A photo eye set has a transmitter on one side of the opening and a receiver on the other. The transmitter sends a narrow beam of infrared light, which people cannot see. The receiver waits for it. When the beam is interrupted, the receiver changes the state of a relay in the control circuit, and the board treats that as an obstruction.

Two arrangements exist. A through-beam pair, as described, separates sender and receiver. A reflective unit puts both in one housing and uses a mirror on the other side to bounce the beam back. Through-beam is more dependable over distance. Reflective is simpler to wire, because power only needs to reach one side.

During closing, a broken beam makes the gate stop and reverse. During opening, many boards ignore the beam or pause. The reason is simple: a closing gate is the dangerous direction for something standing in the doorway, while an opening gate moves away from it.

Where to mount photo eyes

Height is the first decision. Place the beam too high and a small child, a pet or a low vehicle part passes under it. Too low and it picks up weeds, shrub leaves or a sprinkler spray. A common practice is to mount two sets, one near knee height and one higher, so more of the opening is covered.

Position along the travel path matters too. Eyes should sit across the line the gate will pass, not behind it. For a swing gate, each leaf needs eyes covering its arc. For a sliding gate, the beam should cross the opening at the closing edge.

Alignment is critical. The beam is narrow, and a small bump to a mount can pull it off target. Most units have a small light that shows when the beam is received. Aim until the light is steady, then tighten the mount. Sun can dazzle a receiver at certain times of day. A small hood or a careful choice of mounting side usually solves it.

Keeping lenses working

Lenses collect dust, moisture film, pollen and the webs of small spiders. Any of these can weaken the beam enough to cause intermittent faults, particularly when the gate is cold and damp in the morning. Wipe the lenses with a soft cloth a few times a year. A drop of water spot or a smear can matter as much as a solid blocker.

Insects like to nest in warm housings. If the gate trips for no clear reason, open the housing and look. A tiny cobweb across the lens is a classic culprit.

The edge sensor in detail

An edge sensor is a strip, often rubber or foam, running along the front or back edge of the gate. Inside the strip is a switch that closes when the strip is squeezed. It can be a pair of conductive surfaces that touch, a hollow tube with an air pressure switch, or an optical sensor inside a clear channel.

When the edge is pressed against something, the gate stops and reverses. Because it only reacts on contact, the edge is a backup to non-contact devices. But it covers situations a beam cannot: the closing edge as it nears a post, a pinch point along a fence, the end of a swing leaf as it presses toward a wall.

Edge sensors need a way to send their signal across a moving leaf. Options include a coiled cable, a cable chain, or a wireless transmitter fixed to the leaf. Cables can wear out from repeated flexing, and a broken wire looks like a constant fault. Wireless units avoid that problem but use batteries.

Monitored sensors

Better control boards monitor their safety devices. They send a small test signal and expect a specific response. If the device is disconnected or damaged, the board knows. It may refuse to close the gate, run it only while a button is held, or flash a fault code. This design prevents a silent failure that leaves the gate unprotected.

Many edges use a resistor in the circuit so the board can distinguish pressed, released and broken states. Installers must wire them with the correct type for the board. Mixing types can cause false alarms or, worse, hide a failure.

Common problems and fixes

• Gate will not close and a light blinks: check the photo eyes for alignment, dirt and webs.
• Gate reverses halfway: look for a swaying branch, a blowing leaf or reflection in the beam path.
• Edge always triggered: inspect the cable for pinches and the strip for damage or compression from a bent frame.
• Gate works only in hold-to-run mode: a monitored device is reporting a fault.
• Sensor works on dry days only: moisture is entering a housing or connector.

Never bridge a sensor with a jumper to make a gate work. That removes the protection the sensor was installed to give.

Testing monthly

Block each beam with a cardboard box while the gate closes and confirm it reverses. Press each edge by hand and watch the response. Check the lights on the receivers. Write the date on a card inside the control box. A few minutes each month keeps the gate trustworthy, and it builds familiarity with how the system sounds and moves when healthy.

Together, photo eyes and edges form complementary layers. The beam tries to prevent contact, and the edge limits harm if contact happens. Used with correct force settings and sensible speed, they protect people, pets and vehicles.