Abstract: A system for controlling production in an oil well comprises a first level sensor mounted upon the outer surface of the tubing near the lower end of the tubing and a second level sensor mounted upon the outer surface of the tubing above the first level sensor. The first level sensor is tuned to a first electrical signal frequency. The second level sensor is tuned to a second electrical signal frequency. A control device at spaced intervals transmits electrical signals of the first and second frequencies down the oil well and senses the liquid level by detecting impedance.

Abstract: A system for controlling production in an oil well comprises a controller for activating the means for causing reciprocation of the sucker-rods; a sensing means secured to the outer surface of the production tubing near the lower end thereof comprising a radioactive source spaced from a radioactivity detector such that oil at that level will fill the said space, means associated with said radioactivity detector for counting the output of the detector and establishing an "off signal" when the frequency of the output is indicative of no oil in the said space; means for converting the "off signal" into an acoustical signal directed up the borehole; and receiving means at the top of the borehole for detecting the acoustical representation of the "off signal" and transmitting it as an electric signal to said controller.

Abstract: A comparator for selecting from two air sources, air which requires less energy to condition includes a humidity and a temperature sections for comparing relative humidities and dry-bulb temperatures of air from each of the sources. Each section comprises two chambers separated from each other by a diaphram which is displaceable in the direction of the chamber having a lower pressure. A temperature post is attached to the diaphram of the temperature section and a humidity post is attached to the diaphram of the humidity section. The pressure in each of the chambers is determined by the pressure signal generated by a transmitter and it indicates the sensed condition. The post of the humidity section coacts with the post of the temperature section to give an output signal indicating which of the two air sources has a lower enthalpy except that when the humidity of the outside air is lower than that of the return air. In that instance, the temperature section alone determines the output signal.

Abstract: A system for controlling production in an oil well comprises a first level sensor mounted upon the outer surface of the tubing near the lower end of the tubing and a second level sensor mounted upon the outer surface of the tubing above the first level sensor. The first level sensor is tuned to a first electrical signal frequency. The second level sensor is tuned to a second electrical signal frequency. A control device at spaced intervals transmits electrical signals of the first and second frequencies down the oil well and senses the liquid level by detecting impedance.