Example:  Abrupt Stops

This hotel elevator was stopping abruptly between floors and entrapping passengers about once a week. The behavior had been occurring for several months, and technicians were unable to resolve the problem.

QarVision™ was installed, and the recorded data shown in the annotated graph at left enabled the maintenance company to diagnose and fix the problem. Items in the graph are:

  - Blue bars - normal accelerations
  - Red bars - brief accelerations
  - Solid yellow - door open
  - Yellow hatch - door opening or closing
  - Gray hatch top - door interlock closed
  - Gray hatch middle - safety string closed
  - Gray hatch bottom - brake disengaged

The elevator started making a normal upward trip at high speed, when suddenly the door interlock relay opened. This in turn caused the safety string to open, and shut the elevator off. The brake coil then de-energized, causing an abrupt deceleration followed by a bouncing of the car. Then about 20 seconds later, the door interlock closed by itself, resetting the other relays, and allowing the car to continue on its trip. The same behavior happened on the next trip. When the recorded data were examined, it showed that this was happening quite often.

Using the data collected by QarVision™, the technician quickly found that the problem was caused by an intermittent switch on one of the landing doors.

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