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.
