How to Control an Automatic Door Using Infrared Photoelectric Sensors

Automatic doors are a standard feature of commercial buildings, warehouses, clean rooms, cold storage facilities, and countless industrial applications. Whether the door is a sliding panel, a rollup overhead door, or a swing door, infrared photoelectric sensors provide the non-contact detection capability needed to open the door when someone approaches and — critically — to prevent the door from closing when a person or object is in the door opening. This guide explains the principles of photoelectric door control and the correct approach for integrating sensors with an automatic door system.

Why Photoelectric Sensors Are Essential for Automatic Doors

An automatic door without reliable presence detection is a safety hazard. A door that closes on a person, a forklift, or a product load can cause injury, equipment damage, and production downtime. Mechanical detection methods — pressure mats, physical contact sensors, or floor-mounted treadles — require the door to make or nearly make contact with the object before stopping, which is inherently less safe than non-contact detection.

Infrared photoelectric sensors detect the presence of people and objects before any contact occurs. The sensor's output tells the door controller to keep the door open as long as anything occupies the door opening, and to begin closing only when the area is confirmed clear. Because there is no physical contact required between the sensor and the detected object, there is nothing to wear out from repeated activations, and the system remains responsive from day one through years of continuous service.

Choosing the Sensor Configuration

For automatic door applications, the through-beam (opposed-mode) configuration is strongly recommended over retro-reflective or diffuse proximity mounting.

In a through-beam setup, the transmitter is mounted on one side of the door opening and the receiver is mounted directly across on the other side. The transmitter emits an infrared beam that travels the full width of the opening to the receiver. Any person or object that passes through the opening interrupts the beam, triggering the door controller.

Why through-beam instead of retro-reflective? A retro-reflective system uses a reflector mounted on the opposite side of the door opening. In practical door applications, that reflector will accumulate dirt, grease, condensation, and physical wear very quickly. A dirty reflector reduces the beam's return strength, leading to unreliable detection. Maintaining a clean reflector in an active industrial or commercial doorway is a constant maintenance burden. Mounting the receiver directly across from the transmitter eliminates the reflector entirely and delivers a stronger, more reliable beam with no additional surfaces to maintain.

Selecting the Right Sensors

For door applications, consider the following selection criteria:

IP rating — in industrial environments, loading dock doors, cold storage entries, and washdown areas all subject sensors to moisture. Select sensors with at minimum an IP67 ingress protection rating for any application where water spray, condensation, or cleaning is a factor.

Sensing range — the sensor range must comfortably exceed the door opening width, with margin to spare. Wider openings require sensors with greater range.

Response time — door control requires sensors that respond quickly to detection changes, particularly for fast-cycling high-speed doors. Verify the sensor's response time is suitable for the door speed.

External amplifier systems — for heavy-duty applications or wide door openings, photoelectric systems with separate transmitter/receiver heads and an external amplifier provide greater power and longer range than self-contained sensors. The amplifier also provides easier access to sensitivity adjustment without climbing up to the sensor mounting position.

Wiring the Output: Normally Closed Logic

The output configuration of the photoelectric system is a critical design decision for door applications, and the correct choice is normally closed (NC) output mode.

In normally closed mode, the relay output of the photoelectric amplifier is closed (conducting) when the beam is present and clear. When the beam is blocked by a person or object, the relay opens (stops conducting).

Why Normally Closed?

Using normally closed output for a door hold-open function means that the door controller interprets the loss of the relay signal as an instruction to hold the door open. This creates a fail-safe condition:

• If the sensor loses power, the relay opens, and the door holds open.
• If the sensor cable is cut or develops a fault, the relay opens, and the door holds open.
• If the beam is blocked by a person in the doorway, the relay opens, and the door holds open.

In every failure scenario, the door opens or remains open rather than closing. This prevents a door from closing on a person due to a sensor malfunction, which is the correct safe-fail behavior for any door application.

If the output were configured in normally open mode — where the relay closes when the beam is blocked — a loss of power or a cable fault would cause the relay to open, which the door controller might interpret as a clear signal, potentially causing the door to close even with a person present. This is an unsafe condition and should be avoided in door applications.

Programming the Door Controller

The door controller (PLC) must be programmed to interpret the sensor logic correctly:

• Relay closed (beam present, opening clear) — this is the "safe to close" condition. The door may proceed to close when commanded by the primary door trigger (push button, motion sensor, or timer).
• Relay open (beam blocked OR sensor fault) — this is the "hold open" condition. The door controller must not initiate or continue a closing sequence.

In practice, the door controller logic typically works as follows:

1. A trigger signal (button, access card, motion detector) commands the door to open.
2. The door opens fully.
3. A timer begins counting down a hold-open period.
4. At the end of the hold-open period, the controller checks the photoelectric sensor status.
5. If the sensor relay is closed (opening clear), the door begins to close.
6. If the sensor relay is open (obstruction present or sensor fault), the close command is suppressed and the controller continues monitoring.
7. Once the relay returns to closed and the opening is confirmed clear, the door closes.

This logic ensures the door never closes when the opening is occupied and never closes due to a sensor failure.

Mounting the Sensors

Mount the transmitter and receiver at a height appropriate for the types of objects that must be detected. For pedestrian doors, mounting at approximately waist height (3 feet) detects most adults and children reliably. For vehicle doors and loading dock applications, mount sensors at a height that detects the full range of vehicles and loads that will pass through, typically requiring multiple sensor heights or a light curtain array for complete coverage.

Use mounting hardware that holds the sensors rigidly and does not allow vibration or thermal expansion to shift the alignment over time. Even modest misalignment of a door sensor can reduce the beam power margin and lead to intermittent operation.

After mounting, align the sensors carefully using the string method or the built-in LED alignment indicator on the amplifier. Make fine alignment adjustments to the transmitter only after rough alignment of both units.

Ongoing Maintenance

Automatic door sensors require periodic maintenance to maintain reliable operation:

• Lens cleaning — clean the sensor faces with a soft cloth and mild cleaner at regular intervals. Grease, dust, and condensation accumulate on the lens surface and reduce beam power.
• Alignment checks — verify alignment monthly. Door frames flex, mounting hardware loosens, and thermal cycling shifts sensor positions over time.
• Amplifier enclosure integrity — for systems with external amplifiers in protective enclosures, verify the enclosure seal is intact at each maintenance visit.
• Functional testing — periodically test the fail-safe behavior by disconnecting the sensor power with the door in the closed position and confirming the door opens or remains unable to close.

A correctly specified, properly installed, and regularly maintained photoelectric door sensor system provides reliable, safe door operation across years of continuous service in demanding commercial and industrial environments.