Elevator light curtain is a kind of door safety protection device based on photoelectric induction principle. It is used on passenger and freight elevators to ensure passenger safety when getting in and out.
The light curtain consists of two main parts: a transmitter and a receiver.
- The transmitter contains multiple LEDs that send pulses of infrared light to the receiver. The pulses emit in sequence, such as from top to bottom, and each pulse releases at a specific frequency.
- The receiver pairs with the transmitter to “expect” these pulses in the right sequence and timing, thereby eliminating (or nearly eliminating) the possibility of interference from other light sources.
When an opaque object passes between the transmitter and receiver, that object interrupts the reception of pulses. This interruption triggers the elevator door to stop.
Light curtain common Failures:
1. Miss operation: elevator doors can’t close
As a type of closed-loop protection system, elevator doors can’t close when infrared beam detection circuit breaks off.
Following hardware failure may lead to abnormal interrupt of the circuitry:
- Light spot is blocked by foreign bodies------check the light curtain beam path and clear foreign bodies.
- Dusty infrared transmitter and receiver caused by long-term use of light curtains, or used in dusty, humid conditions ----- just clean up the dust.
- Damaged light spot caused by the breakdown of the infrared transmitter tube--- just get a new one.
- Damaged light curtain shell creates a shadow around injured areas and blocks infrared emission--- replace it with a new one.
2. Miss operation: elevator door closing interrupt
If the scanning beam is not received or fails the reception level, elevator doors will stop closing and then open during the closing process. This occurs when there is an obstruction in the way or inner core injury of the cable.
3. Light curtain does not function
This means during the closing process, obstructions cannot break the close loop to trigger an automatic stop signal. Possible causes:
- Low density of infrared light beams, or scan mode creates blind areas.
- Low infrared sensitivity: the emission intensity of the light curtain reaches its maximum when elevator doors are fully open, then decreases step by step during the closing process (each stage lowers to the minimum accepted level to avoid action failure as the prescribed minimum), and the emission intensity reduces to the minimum when doors are completely closed. If not, small obstacles can’t block infrared rays when there is little distance between elevator doors, which makes the doors keep closing.
- The receiver captures infrared light of similar wavelength from wrong sources, such as the sun light and elevator backlighting.
