Abstract: A sensor disposed in the ground has a characteristic which changes generally predictably in relation to the moisture content of the ground. A signal is produced by a circuit during a period of energization whenever the characteristic of the sensor is at or beyond a threshold. The signal, once produced, is held during said period of energization, the energy being provided by a source of periodic energization for a solenoid driven water valve. A gate passes the periodic energization to the solenoid whenever said signal is present. When the periodic energization ceases, said signal ceases and the water valve closes. If the characteristic of the sensing element is not at or beyond said threshold during a period of energization, said energization is not gated to the water valve solenoid and the water valve remains closed.

Abstract: Apparatus for providing the voltage transformation functions of a conventional electrical power transformer. An AC input signal is chopped in a solid state switching converter at a frequency very much larger than the frequency of the input signal and then filtered to attenuate the high frequency component while passing the frequency of the AC input signal. The switching converter includes a pair of bidirectional solid state switches, an inductor and a capacitor connected in a buck converter, boost converter or buck-boost converter arrangement to provide a step up, step down, or step up/step down capability, respectively. A feedback signal modulates the duty cycle of the switching converter to provide automatic voltage regulation under varying loads and leading and lagging power factors.

Abstract: A power converter which provides precise waveshape regulation. An input pr waveform (three-phase or single phase power) is rectified and modulated to form a chopped waveform within an envelope defined by the rectified input waveform. The modulation is removed by passing the chopped signal through a low-pass filter. The output of the low-pass filter, which is equal to the instantaneous value of the chopped waveform envelope times the instantaneous value of the duty cycle of the chopped waveform, is converted to a complete sine wave output voltage in a power inverter. The output of the power inverter is sampled and compared with a low-power reference waveform in a differential amplifier. The output of the differential amplifier is phase compensated for the effects of the low-pass filter and applied as an error signal to a pulse-width-modulated oscillator to adjust the duty cycle of the chopped waveform so that the sine wave output voltage follows the reference waveform.

Abstract: An active power-line filter which provides bandpass filtering and transient uppression. The high-power signal to be filtered is modulated to form a chopped waveform within an envelope defined by the input waveform and the modulation is removed by passing the chopped signal through a low-pass filter. The output of the low-pass filter is then compared in a differential amplifier with a low-power reference signal which is phase-locked to the primary component of the high-power signal. The output of the differential amplifier is phase-compensated for the effects of the low-pass filter and is compared to the reference in a phase-detection multiplier to produce an error signal to adjust the duty cycle of the chopped waveform so that the waveform at the output of the low-pass filter is identical to the reference waveform.

Abstract: A system for measuring the transfer immitances, impedance and admittance, a linear electrical network having one or more ports. The system utilizes clamp-on ferromagnetic cores to electromagnetically couple the transfer immitance measuring system to the electrical network without having to interrupt the normal on-line operation of the electrical network. A high frequency injection network, which includes a high frequency signal generator and a multichannel amplifier, injects a high frequency signal into each of the ports of the electrical network. High frequency voltage and current measuring networks are electromagnetically coupled to each of the ports of the electrical network to measure the high frequency component of the port voltage and the port current.

Abstract: A base insulator design for VLF antennas. A surface insulating material, h as glass, serves to provide a long surface distance between the upper and lower metallic components of the base. A thin, soft metal cover extends the base metal conductor out to the edge of the outer insulator and also provides a weather shield for the internal components. An insulator core of porcelain serves to take up all of the mechanical stress in the structure and a dielectric fluid serves as a coolant which also protects the inside surface from contamination.