Abstract: A video system measures the position of the traveling block of a drilling rig to determine borehole depth and the rate of drill bit penetration. A television camera is arranged to track the vertical movement of the traveling block of a drilling rig between its uppermost and lowermost positional limits. An encoding unit is connected to the television camera. The output of the encoder indicates the block's position along its vertical path of movement. The output signal is processed to provide information such as borehole depth and drill bit penetration rate. The output may be in the form of an analog output to a dial indicator, a chart recorder or the like. The system is not subject to fouling or mechanical failure and the system, including the input sensor, may be located in its entirety remotely from the drilling rig.

Abstract: An accurate measurement of the level of drilling mud in a mud pit is provided using an ultrasonic transducer that includes ambient temperature correction. A cylindrical metal shroud open at the bottom is positioned around the transducer. A series of vent holes are located along the upper area of the shroud to allow the convection of ambient air. A series of Nylon screws extend through the shroud close to the transducer to limit lateral movement of the transducer within the shroud. As the shroud and transducer become heated by sunlight, ambient air is circulated from the surface of the drilling mud upward to the transducer through the space between the transducer and the sidewalls of the shroud and out through the vent holes. The chimney effect thus produced insures that the temperature correction accurately represents the temperature of the ambient air between the drilling mud and transducer.

Abstract: An elongated manually manipulable housing contains a photocell at one end for sensing energy levels in the visible frequency spectrum causing said photocell to correspondingly change in electrical conductivity. A portable power source in the housing is coupled to the photocell to provide an electrical signal corresponding to the change in the photocell conductivity. A comparator circuit in the housing compares that signal with an adjustable reference signal to provide an output signal upon a predetermined ratio between the compared signals. A multivibrator circuit in said housing is coupled to said comparator circuit and to a vibration-generating means which produces signals preferably in the audible range, so that upon the occurrence of an output signal, a user discernible, either audible or tactile, vibratory signal is generated.