The graph at left shows accelerations
and door activity in an elevator that is frequently making extra
trips. The building manager reported that the elevator was traveling
a lot. When the technician arrived, it was working perfectly.
Installing QarVision revealed what was happening.
Blue bars - acceleration / deceleration
of duration greater than 420 msec. Height of bar is maximum
Yellow bars - door
opening, open, and closing.
In the first trip (far left), the car
travels down (first 2 blue bars) then immediately travels up (next
pair of blue bars). When
it stops, the door does not open.
In the last trip (far right), the car
travels up, then immediately travels down. When it stops, the door
The problem was a non-functional
group controller. There were 3 elevators in the group, and all three
were attempting to answer each call. When the group controller was
down, this elevator answered a call by traveling to the nearest
terminal, then traveling to the floor, resulting in two trips in
opposite directions. In the first trip at left, by the time this
elevator arrived at the floor, another had already answered the
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