Abstract: Damage to electronic golf course sprinkler valve controls from lightning current surges is prevented by electrically isolating the actual valve control circuit from the logic circuitry that controls it, using in the valve control circuit only components and printed traces that can withstand at least as much power dissipation as the field wiring, and grounding each valve control individually to earth ground through a plasma discharge device.

Abstract: An ultrasonic generating system for coupling vibrating energy into a load, such as living tissue, has been described which employs a piezoelectric crystal having excitation electrodes on opposite faces thereof. A feedback electrode is disposed on one face of the crystal adjacent to and insulated from one of the excitation electrodes to provide a feedback signal between the feedback electrode and the other excitation electrode. A power supply is provided for applying excitation energy to the excitation electrodes. The feedback signal is utilized to slave the frequency of the power supply voltage to the resonant frequency of the crystal and to disable the power supply when the impedance of the load applied to the crystal rises above a predetermined level.