Basset convergence system Applications The Bassett  convergence system provides automated surveys of a tunnel section. Typical  applications include: Recording the behavior of tunnels and other underground openings to verify  that actual performance conforms to predictions. Monitoring deformation due to nearby construction activity or to slope  movements and other natural disturbances. Monitoring deformation in tunnels under construction to ensure safety and to  control the rate of construction. Operation The  Bassett system uses tilt sensors to monitor the position of reference pins  installed in a tunnel section. The sensors are linked to the pins via a system  of low-profile arms. Spatial displacement of the pins results in changed tilt  readings. A complete survey of a typical tunnel section requires about five  seconds. Seconds later, a computer automatically retrieves the tilt readings  from the data logger in the tunnel, calculates displacement data, and generates  a graphic display. The system can be configured as a closed loop or left open-ended. With closed  loops, a Bowditch correction can be applied to minimize the effects of errors.  Open-ended systems are referenced to conventional surveys periodically unless  one end is known to be stable. Advantages High Resolution: The Bassett system can detect deformations as small  as 0.02 mm. High Precision: The Bassett system relies on tilt sensors rather than  optics, eliminating errors due to variations in the refractive index of air in  the tunnel. Near Real-Time Data: Displacement data can be generated within seconds  of logging. Graphic Displays: Customized software computes and displays  deformations in graphic form. Low Profile Design: The system fits close to the tunnel wall and does  not interfere with normal traffic. Arms can be shaped to provide extra clearance  or to bypass obstructions. Robust and Reliable: The system tolerates vibration, temperature  fluctuations, electromagnetic emissions, and minor impacts.