Elevator Surveillance Guide

 Elevator Surveillance Guide

Installing surveillance in an elevator can be challenging. Small but wide areas, vandal resistance, and transmission methods all present challenges not found in other areas cameras are installed. In this note, we look at:

• Form factor: Box vs. dome vs. specialty
• Resolution: How much is necessary?
• Transmission: Wired vs. wireless vs laser methods
• Dealing with electrical contractors

Form Factor

The first decision to make when considering elevator cameras is form factor. Minidome and corner mount are the two most common options in use as they most compact compared to box, bullet, or full sized dome cameras. Other form factors, such as box or bullet may be more easily tampered with due to the low ceiling height of the elevators, and more easily knocked out of position.

Minidome

The key advantage to minidomes is camera choice, as most manufacturers offer cameras in this form factor, with numerous resolution and lens options. These options are not generally seen in corner mount cameras.

However, they are more obtrusive than many corner mount housings, and do not blend into the interior of the elevator as well. Where aesthetics are the key concern, domes may not be preferred.

Corner Mount

This type of mount places the camera in a roughly triangular housing made to cover one of the elevator's corners. Some are sold as unitized housing/camera packages, while other manufacturers sell housings meant to accept a box camera. Size and appearance varies depending on manufacturer:

They key drawback to corner mount cameras is limited availability. Most manufacturers do not offer corner mount options, and those that do typically only offer one or two models, with limited resolution and lens choices. Larger corner housings built for box cameras add more flexibility, but are larger and more obtrusive.

Field of View/Resolution

Given elevators' small size, generally under 10' wide, users typically choose to cover the full car instead of just the doors. This gives them not only the opportunity to view comings and goings, tracking subjects throughout a facitity, but to view potential incidents in the elevator, as well. However, care should be taken that pixels per foot (PPF) does not drop below acceptable levels for recognition if no other cameras will provide facial shots of subjects, e.g. lobby and hallway cameras.

For example, using an actual 103° field of view from an elevator camera with Camera Calculator, we can see the difference between VGA, 720p, and 1080p in a typical 8x8' elevator. Estimating ~9' to target to reliably capture subjects as they enter through the elevator doors, 720p provides 56 PPF in this scene. This is likely enough to provide identification quality video under good lighting. VGA provides only 28 PPF, too low for recognition, while 1080p provides 85, more than enough.

Mounting Height

Since most people look down while walking, and criminals may actively avoid cameras, mounting height in elevators should be carefully considered for the best chance of capture. As we found cameras are typically best mounted as low as possible, with ~8' being a "sweet spot", better able to see those with heads down or hats on while also see over subjects beneath the camera.

This image shows the effects of mounting height and the subject's face angle, displaying the difference in capture quality at various mounting heights with the subject's face level as well as tilted down.

Signal Transmission

Once the camera has been selected, installers must decide how signal will be carried from the elevator. There are three typical options for this:

• Traveler cable
• RF wireless
• Optical laser

Traveler Cable

Connections between the elevator car and the machine room for power and signal are made via a specialized traveler cable. This cable is attached to the car, typically to the bottom, and to the top or center of the shaft. The construction of this cable varies, but it typically contains multiple twisted pair conductors for power and control, and possibly a UTP or coaxial cable for video. 

This image shows cross-sections of various flat traveler cables:

Generally speaking, since these cables are often attached to the top of the shaft, making the cable approximately twice the height of the shaft, UTP is not a usable solution for Ethernet. Buildings of 12-14 stories can easily have a 300' traveling cable, which exceeds the maximum distance category cables can be run, before even considering horizontal runs to an equipment room or IDF. In low-rise buildings, UTP may be an option, however. Fiber-optic and coaxial cables may be considered otherwise.

RF Wireless

The second option is to opt for wireless connectivity, utilizing a pair of wireless APs between the car and bottom or top of shaft. Both are used in practice, with the bottom of the shaft generally chosen for easier servicing. In this case, local power must be obtained from the car, which may involve the elevator contractor. Power is readily available, however, due to lights and air conditioning installed in the car.

Wireless eliminates the issue of necessary conductors in the traveler cable, but presents challenges of its own. Cables and conduits located in the elevator shaft may cause interference, making wireless connectivity unreliable. Very narrow beamwidth antennas may be used to compensate for this, but antenna alignment must be carefully set and maintained over time.

Optical Wireless

Optical wireless uses a pair of laser transceivers, one mounted to the car, the other in the shaft, to send/receive data. This is specified to handle elevator shafts up to 75 floors.

Optical product performance is degraded by dust, dirt, and other debris which may fall in the elevator shaft and as such should be cleaned regularly.

Dealing With Elevator Contractors

Normally, most facilities maintain service contracts with an elevator contractor, since the elevator must undergo routine maintenance. These contractors may be difficult to deal with, as a number of users have shared. They are often hesitant to modify existing traveling cables for new services, simply because it complicates (however slightly) their routine maintenance of the elevator with a system outside their control. If the traveling cable is insufficient to add video, installing a new cable is, most times, cost prohibitive, and may remove the elevator from service for several days. Both of these add up to expenses users may not wish to incur.

To avoid the coordination and expense required to have the elevator vendor add video to a car, users and integrators may attempt to add their own cable to the car. There are two things to be aware of in this case: 

• Third parties attempting to modify the cable without the contractor's permission will void warranties and service contracts in most cases. Even leaving existing cables alone and simply zip-tying a new UTP cable to it may be frowned upon.
• According to NEC code, hoistway cables must be listed for use in these applications, and be of type E. Standard UTP, fiber, and coaxial cables do not meet these requirements.