Access Control Door Held Open by a Failing Request-to-Exit
You service a card-access door at a medical office. The door uses a maglock, a request-to-exit (REX) motion sensor, a push button, and a door position switch (DPS). The access control panel logs show the door 'held open' alarms every morning around 7 a.m. Staff report the door sometimes stays unlocked for several seconds after they walk away. The maglock is 12 VDC, 0.5 A. The REX sensor is powered from the same 12 VDC supply as the lock, sharing a common. A new fluorescent fixture was recently installed in the hallway near the REX. The fire alarm system is interconnected to release the lock on alarm.
1. Identify the most likely cause of the 'held open' alarms and the delayed relock, and explain the mechanism.
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Most likely: REX sensor false/malicious triggering and electrical noise, compounded by shared power.
Mechanism:
- The new fluorescent fixture near the REX can emit EMI and, more importantly, the REX is a motion sensor that may be seeing hallway activity or fixture flicker/heat. A false REX signal tells the panel 'egress requested,' so it unlocks the door and holds it - producing 'held open' alarms when the DPS still shows the door closed/open mismatch.
- The REX sharing the 12 VDC supply and common with the maglock means lock inrush and switching transients ride on the REX supply/common, potentially causing spurious REX output or delayed release.
- The delayed relock (several seconds after walking away) is consistent with the REX holding its output (adjustable delay) or with noise keeping the REX asserted.
So the 'held open' log entries are the panel reacting to a false egress request, not a bad DPS alone.
2. The fire alarm interconnection must release the lock on alarm. How does that requirement constrain your troubleshooting and any fix?
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The fire release is a life-safety function and must remain fail-safe and reliable at all times:
- The maglock must release on fire alarm (and typically on power loss, per fail-safe design). Any troubleshooting or rewiring must not defeat or delay that release.
- Do not add delays, filters, or changes that could prevent the lock from releasing on alarm.
- Verify the interface (relay/contact from the fire alarm) still drops power to the lock when tested, and document the test.
- If you separate the REX power from the lock supply, keep the fire-release circuit intact and independent of your changes.
Practical constraint: you can clean up REX power/noise, but the fire-release path stays as designed and must be re-tested after any modification. Never 'temporarily' bypass the release to quiet alarms.
3. Propose a corrective plan that fixes the nuisance alarms without compromising security or life safety.
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Corrective plan:
- Separate power: give the REX its own filtered supply (or at least isolate it from the maglock's switched supply/common) to remove lock-induced transients.
- Address the EMI source: relocate or shield the REX away from the new fluorescent fixture; verify the fixture is properly grounded.
- Adjust/verify REX settings: confirm the REX delay and sensitivity are appropriate; a long delay explains the 'stays unlocked' complaint.
- Verify DPS and alignment: confirm the DPS reports door state accurately so 'held open' reflects real conditions.
- Re-test the fire release: confirm the lock drops on alarm after all changes and document it.
- Monitor the log: confirm morning 'held open' events stop.
This fixes the cause (false REX + noise + shared supply) while preserving security (lock holds when door closed) and life safety (releases on alarm).