Bi-directionally dynamically braked gate crossing mechanism controller

Abstract From the Canadian patent

The output voltage of a D.C. motor used to raise and lower a railroad crossing gate is monitored to detect when the D.C. motor begins to generate power indicating that the motor is being driven by a rising gate arm. If the motor generates power above a adjustable predetermined value the gate arm mechanism is considered to be operating too fast whereupon an impedance is shunted across the motor's armature thereby applying a load to the generating motor. The electrical load causes the motor to act as a dynamic brake slowing the gate arm mechanism operation and reducing the likelihood that the mechanical components of the crossing gate arm mechanism will be damaged.