How do sensors impact elevators?

Perhaps the most obvious sensing performed in modern elevators is the technology used for elevator doors. Or maybe it is the weight sensing that is indicated by the certification plate that specifies the elevator’s weight limit. In any case, safety is the most critical application of elevator sensors. However, security is right up there, too. There are other sensor applications as well.

Elevator safety

Among other aspects, the latest (2022) safety code for elevators and escalators, ASME A17.1-2022, or, in Canada, CSA B44-2022, defines new and clarifies existing requirements for the means of detecting persons or objects between the doors (2D sensing) or approaching the elevator (3D sensing).

Modern elevators use 2 to 8 sensors, including displacement sensors, load cells, light curtain sensors, leveling sensors, speed encoders, and more. Typical sensors and their applications include:

Encoders are used to encode the pulley rotation and determine the elevator position.
Position sensors for pulley rotation sensing and floor position/leveling sensing.
Closed-loop current sensors in inverters for motor control.
Limit switches for elevator car position sensing and buffer system switching.
Hall effect sensors for elevator door position sensing.
Secondary Hall effect sensors for elevator door position sensing.
Limit switches for wire rope slack control.
Magneto-resistive sensors for elevator car position sensing.

In addition to the technologies identified for these applications, radar sensors can ignore people passing laterally in front of an elevator door but react to people approaching the door. With radar, the elevator can hold a door open and allow a passenger to reach the car before closing the door. Using the Doppler principle, the radar sensor measures changes in wave frequency relative to the motion of an object or person to ignore people passing laterally in front of the door, but respond to people approaching the door.

While infrared photoelectric sensors were widely used in the past, elevator designers have the option of using cameras and software for motion and presence detection today. However, light curtains with multiple photoelectric light beams create a crisscrossed curtain effect across the elevator door opening. With this design, a passenger only needs to break a single beam to trigger an output for control.

Other sensors include overload sensors to detect when the car carries more weight than it is designed to hold. If the weight is too heavy, the elevator will not run. In addition, displacement and leveling sensors provide elevator leveling control and adjustment to achieve automatic leveling. However, in the unlikely event of a free fall, a governor system activates if the elevator’s speed exceeds a safe limit.

Security

Many of today’s elevators have integrated security systems that can include keycard access for restricted floors, surveillance cameras, and alarms. In addition to preventing unauthorized access, they ensure passenger safety by closely monitoring elevator usage and maintaining a secure environment.

Conserve energy

One way to reduce energy consumption in an elevator is to turn off the lights when the elevator is not in use. This involves a motion detector. By sensing motion or its absence, when no motion is detected after a specific amount of time, the elevator’s control system can turn off the cabin lights. When the doors open for a passenger to enter, the lights can be turned on.

Special applications

For specific applications, like hospitals, a time-of-flight spotlight can detect when a bed or other transportation device is placed in an elevator. When the sensor detects a bed, the elevator’s control sends the elevator directly to the floor selected by the person accompanying the patient.