Example:  Group Controller Non-Functional
 
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 acceleration.

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 opens.

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 call.

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