Abstract: A weld detection system for a pipeline survey pig includes a plurality of weld sensor units mounted spaced apart circumferentially on fore and aft pig support members and arranged in close proximity to the pipe wall. The sensor units comprise permanent magnet members for generating a magnetic flux field around a wire coil which is modified upon passing a girth weld or other magnetic anomaly in the pipe to produce a voltage signal which is conditioned by an amplifier and filter circuit to a signal suitable for input to a digital activation circuit. The digital activation circuit receives conditioned signals from opposed pairs of sensor units on the support members to distinguish transverse girth welds from spiral or longitudinal welds. The digital activation circuit includes circuit elements for timing the sensor output signals of the fore and aft detector arrays for measuring the velocity of the survey pig through the pipe.

Abstract: The present invention is directed to a method and apparatus for maintaining steady state conditions in a separator. Steady state is maintained by controlling mass flow rates of influent to, and underflow from the separator. Specifically, an influent specific gravity and flow rate signals are monitored by an influent mass flow controller. That controller responds to variation in these signals to maintain a constant mass feed rate into the separator. A mass flow signal, comprising a composite of influent specific gravity and influent mass flow signals, is produced. That signal is fed to a thickener controller which also monitors mass flow of the underflow. The thickener controller adjusts the mass flow rate of the underflow in response to the influent mass flow signal. However, fluctuation of an interface level between clear and unclear areas of the thickener can effect flow rate adjustment.