The Model BSD (belt speed detector) is a “traction action” motion control that indicates when a conveyor belt has slowed or quit moving altogether. The unit can be adjusted as an overspeed, underspeed, or zero speed control. The output of the Model BSD can be wired into a PLC or DCS, or to the optional RMS controller (or MSD controller) which has a DP/DT relay to control up to two separate circuits, one for machinery shutdown and one for an alarm. The Model BSD can shut down rotating equipment before damage is encountered. It provides protection for interlocked conveyor belts, especially if one of the belts fails due to overloading or quits due to tearing. The standard construction is a mild steel/carbon steel frame with safety yellow polyester powder coating. The main advantages of the Model BSD are no drilling or tapping of tail pulley shaft required, the unit is shielded between top and bottom of conveyor belt, and the unit can be placed anywhere on the conveyor belt.