Commercial Swing Gate Sharing a Lane with a Card Reader and Loop Detector
A 16 ft (4.9 m) dual-leaf swing gate serves a commercial parking lane. Vehicles approach a pedestal card reader; an in-ground exit loop is located 6 ft past the gate on the secure side. The free-exit loop is 4 ft from the gate on the approach side. The installer wired the free-exit loop to the operator's 'open' input and the safety loop to the 'stop' input. During a test, a truck stopped on the free-exit loop holds the gate open indefinitely, and a second vehicle following closely is struck by the closing leaf because the safety loop is inside the swing arc and does not detect it. Pedestrians can walk around the pedestal into the swing path. No presence sensors are installed on the leaves.
1. Diagnose the loop wiring and placement errors and state the correct functional assignment for each loop.
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Two errors compound.
Wiring/function:
- The free-exit loop should command an open (and typically hold-open while occupied) for exiting traffic; wiring it to 'open' is directionally right, but it must not be able to hold the gate open indefinitely in a way that blocks the lane. The symptom (truck parked on it holds gate open) is expected loop behavior but reveals the loop is too close to the gate/thoroughfare so normal queuing occupies it.
- The safety loop wired to 'stop' is wrong. A safety loop should feed an anti-entrapment/reverse or presence function that prevents closing on a vehicle, not a hard stop that leaves the gate in an undefined state.
Placement:
- The safety loop at 6 ft past the gate on the secure side is outside the swing arc and cannot detect a vehicle in the path. It belongs in the swing path, positioned so the gate cannot close on a vehicle occupying the arc.
- The free-exit loop at 4 ft from the gate is too close; it will be occupied by queued vehicles and cause nuisance holds.
Correct assignment: free-exit loop → open/hold-open for egress; safety loop(s) → presence/reverse in the swing path; card reader → access request; add a separate arming/close loop as needed.
2. Pedestrians can bypass the pedestal into the swing path. What protection is required and where should it be located?
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The swing path is a pedestrian entrapment hazard and must be protected independently of the vehicle loops.
- Install monitored presence/entrapment sensors covering the full swing arc on both the approach and secure sides, positioned so a person standing anywhere in the arc is detected before and during closing.
- Add edge sensors on the leading edges of both leaves to detect contact with a person or object, wired as monitored devices.
- Consider physical guidance (bollards, rails, or a pedestrian gate) to keep walkers out of the vehicle lane, but do not rely on signage alone.
- Verify the sensors are monitored (supervised) so a failed or disconnected device prevents automatic closing rather than silently disabling protection.
All devices must be tested for full-arc coverage, not just at the centerline.
3. How would you re-test the lane after rewiring and adding sensors, and what would you record?
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Run a scripted sequence with two people and a test vehicle:
- Card read → gate opens; confirm no premature close while the vehicle occupies the arc.
- Vehicle parked in the swing path → gate must not close; remove vehicle → gate resumes/close per design.
- Pedestrian standing in arc on each side → gate must not close; edge sensor contact → reverse.
- Free-exit loop occupied by a queued vehicle → confirm intended hold behavior and that it does not deadlock the lane.
- Simulate a disconnected sensor → confirm the operator faults safe (no automatic close).
- Timer-to-close and fail-safe behavior after power loss.
Record loop assignments, sensor locations, pass/fail per test, device models, and any as-left configuration changes on the commissioning form; attach to the handover package.