Abstract: A pump-off controller checks for pump-off by examining the relative phase relationship between AC voltage and AC current supplied to an inductive, alternating current, electric motor driving a cyclically operated mechanical system having a walking beam for raising and lowering a subsurface pump by means of a string of sucker rods. When the phase angle between AC voltage supplied to the motor and AC current drawn by the motor exceeds a predetermined value at selected points or regions of the pumping stroke, the pumping system is shut down for a predetermined time.

Abstract: New apparatus and methods are disclosed for controlling the operation of a rod-pumped oil well. The load on and position of the rod string are measured, an integration calculation related to the work done during a portion of the downstroke is performed, and the result is compared to a reference value, to detect a pumped-off condition in the well.

Abstract: The pump-off controller checks for pump-off by calculating the area inside of a figure whose boundaries are the minimum load, two position lines defined by the user and the load at the time the calculation is being made. This area is compared to a user defined limit to determine whether pump-off has occurred. While the well is running the controller also checks the value of the minimum load, and if it is outside of preset boundaries it readjusts the load signal to locate it within the desired range. The position synthesizer cyclically detects the position of the beam or rod during each stroke and generates a waveform whose amplitude and frequency correspond to the motion of the rod with a period corresponding to the time of each stroke. This information is used by the controller to determine the top of the stroke and to check for pump-off.

Abstract: A process and system for distinguishing between actual and false pump off of a well and for shutting in the well only upon the occurrence of actual pump off. The process and system employs the principle that pump off may occur only after a not pumped off condition has been detected.

Abstract: Strain measuring devices for measuring the strain in the polish rod of a rod-pumped well unit. The devices include a body member to which strain gages are bonded, and further include clamp means for detachably affixing the devices directly to a polish rod. Embodiments are disclosed in which the body member is in the form of a strap, in the form of a split cylinder, or as an elongated bar with a section of reduced cross-section.