Abstract: A mud pulser creates pressure pulses in a stream of drilling fluid circulating through a drill string. The pulser has a body connected into the drill string, and defines a flow passage for drilling fluid. A signal poppet having a piston is reciprocally carried within the body. A lower end of the poppet selectively restricts flow of drilling fluid through an orifice and to thereby increase pressure and creates a pulse while in an extended position. An inner passage with an upward facing servo seat formed therein is located in the body and extends through the signal poppet for the passage of drilling fluid. A motor-driven servo valve selectively engages the servo seat to control flow of drilling fluid through the inner passage. A limit switch responds to axial movement of the servo valve cause the motor to turn off when the servo valve reaches predetermined axial positions.

Abstract: A downhole tool containing instruments and a pulser is landed within a string of drill pipe. The pulser has a pulser body and an orifice on a lower end. A piston slides within a bore in the body and has a signal poppet on a lower end. In an extended position, the signal poppet extends into and obstructs the orifice to reduce the flow of drilling fluid. In an open position, the signal poppet does not obstruct the orifice to increase the flow of drilling fluid. A bidirectional solenoid valve is located above the piston and has upper and lower electromagnetic coils and an axially moveable rod. The rod is movable between a closed position in an opening in the body and an open position away from the opening. The rod is moved to both positions in response to the instruments which sends signals to the coils. The mud pulser also has an on/off flow switch which is actuated by the commencement of mud circulation. Initially, the rod is in the closed position.