Specifications

97Environmental Automation
Equipment includes re alarm control
panels, which are the hub of the
system. The panels communicate
through various means with the BAS,
and potentially directly with the re
department in some larger facilities. They
take inputs from the many sensors and
switches in the system such as smoke
and heat detectors (MAX6682), detectors
of by products of combustion (carbon
monoxide and other gasses), ame
detectors (MAX44006
*
RGB color sensor,
MAX31855 thermocouple-to-digital
converter), detectors of emergency
door use (MAX9621 Hall-eect sensor
interface), and manually activated re
alarm pull stations, and then respond
in several ways. Activation of the re
alarm response includes sounding alarm
bells or sirens; activating strobe lights
(MAX16821 HB LED drivers), exit lights,
and sprinkler systems; and manipulating
HVAC system duct dampers, lighting, and
human transport systems, such as doors,
elevators, and escalators. In factories, the
re alarm response may shut down some
processes and activate others, such as
emergency backup power generators.
Backup Power
Systems
In some buildings, the loss of grid
power can be a critical event. Diesel
generators, battery banks, ywheels,
etc., can all serve as sources of power
for varying periods of time until utility
power is again available. Some facilities
can suer a few seconds of complete
power loss until diesel generators are
powered up and put online. But some
critical facilities are unable to suer
any power loss, so they incorporate
battery banks, ywheels, or other
means to provide a few seconds of
power until the generators are online.
Controllers for backup system startup
and switchover include powerline
sensing, load sensing, computation,
and signaling. Many of these functions
can be provided by o-the-shelf
Maxim parts, but the requirements
vary widely, so these functions will
not be discussed here. Precision,
high-speed, and robust signal
processing is a general requirement
that can be addressed by many Maxim
products found in this guide.
Elevators, Escalators,
and Moving Walkways
Elevator
The building elevator (or lift) is the
vertical transporter for people and
freight in multiple-story buildings. The
smallest elevators (“dumbwaiters”) are
used for freight or food service between
oors. Elevators can carry large groups
of people or pallets of freight. The
largest to date can carry 80 people or
over 11 thousand pounds (5000kg). In
large buildings, such as hotels or oce
buildings, elevators are usually driven
by electric motors and cable systems,
but in buildings with approximately
less than seven oors, elevators use
hydraulic cylinders and pumps.
With the advancement of elevator
technology and the importance of
elevators in high rise buildings, the
elevators now use electronic controllers
with signicant computational capability.
During rush hours, multiple requests for
the elevator can occur simultaneously
from multiple oors. The controller must
allocate elevator resources accordingly
among multiple elevators, if there
is more than one in the facility, and
within each elevator in the system.
Requests from outside the car and from
inside the car all impact the resultant
operating parameters such as direction,
acceleration and deceleration rates, top
speed based upon expected distance,
and timing of responses to new requests
based on car location and current speed.
Depending on the use of the elevator,
controllers adjust the movement of the
elevators. A hospital elevator moving
fragile patients may need to start and
stop very gently, while a freight elevator
may need to handle extremely heavy
loads slowly. An express elevator in a
skyscraper may need to accelerate to
high speed to reach upper oors quickly.
Hotel elevators may need to provide
a good compromise between speed
and comfort. The control algorithms
are usually based on “Up Peak Round
Trip Time” calculations described in
the Guide D: Transportation systems in
buildings of the Chartered Institute of
Building Services Engineers (CIBSE).
In the event of re or other emergency,
elevators are usually commanded
to park at the ground oor and not
to respond to requests for service.
Yet some emergency elevators are
employed for people with disabilities.
AC induction motors driven by VFDs
provide a convenient system to
provide the required variable torques,
accelerations, and speeds under widely
varying loads as users and freight come
and go. With the use of regenerative
VFDs, deceleration forces can be created
by the VFD pumping electrical energy
back onto the grid, thus saving energy
instead of throwing it away as heat.
Counterweights are often used to reduce
the peak motor power required.
Modern elevator in high-rise building.
*Future product—contact the factory for availability.