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The preferred pulser is a mud powered oscillator powered by the pressure variation produced across the signal valve by the unstable action. The signal valve comprises a poppet and cooperating orifice. The pressure drop across the orifice is used to urge the poppet away from the orifice and an opposi

The preferred pulser is a mud powered oscillator powered by the pressure variation produced across the signal valve by the unstable action. The signal valve comprises a poppet and cooperating orifice. The pressure drop across the orifice is used to urge the poppet away from the orifice and an opposing spring drives it toward the orifice. The preferred poppet control is a permanent magnet that secures the poppet in at least the signal valve open position. To generate a pulse, the permanent magnet is opposed by a magnetizing coil arranged and powered by the associated MWD instrument to oppose the permanent magnet, to release the poppet to close the signal valve. The pulser is arranged to provide a generally central axially extending bore to accept a conductor extending axially through the pulser. Optional features include an acceleration compensator, and a mud powered electric energy generator. Optional features include hydraulic actuation and control of the poppet. The poppet can be fitted with an automatic pulse pressure amplitude control. The poppet can use overtravel to produce the on-pulse dwell time required to build pulse signal energy rather than the use of energy to hold the signal valve closed. Various mounting options are provided.

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The invention claimed is: 1. A pulser apparatus for use in wells, in a pipe string, to generate brief pressure changes in a mud stream flowing down the pipe string bore, in response to a down hole instrument, to convey information from the lower end of the pipe string to the surface, the apparatus

The invention claimed is: 1. A pulser apparatus for use in wells, in a pipe string, to generate brief pressure changes in a mud stream flowing down the pipe string bore, in response to a down hole instrument, to convey information from the lower end of the pipe string to the surface, the apparatus comprising: a) a housing arranged for selected location in the bore of said pipe string; b) an orifice, having an upstream side and a downstream side, situated in the bore of said pipe string through which at least part of said mud stream flows; c) a poppet situated in said housing and arranged to cooperate with said orifice to comprise a signal valve to vary the resistance to the flow of said mud stream to vary the pressure drop across said orifice; d) a first piston surface on said poppet and an opposed second piston surface on said poppet; e) a first fluid pressure conducting channel arranged to conduct fluid pressure from the downstream side, as defined herein, of said orifice to said first piston surface; f) a second fluid pressure conducting channel arranged to conduct fluid pressure from the upstream side of said orifice to said second piston surface; g) a poppet position controller, intermittently secured to said poppet, responsive to said instrument, to determine at least one controlled position of said poppet relative to said orifice; h) a spring arranged to urge said poppet toward said orifice; i) said piston surfaces and said spring so arranged that said poppet is urged toward said orifice when said pressure drop across said orifice is less than a preselected amount and is urged away from said orifice when said pressure drop across said orifice is more than said preselected amount. 2. The pulser apparatus of claim 1 wherein said first fluid channel extends through a generally central bore of said poppet. 3. The pulser apparatus of claim 1 wherein said pulser, if un-restrained, will oscillate between axial travel limits. 4. The pulser apparatus of claim 1 wherein said position controller comprises a permanent magnet, an electric coil capable of neutralizing the permanent magnet in response to electric energy from said instrument, and a plate attached to said poppet for attraction to said magnet. 5. The pulser apparatus of claim 4 wherein said permanent magnet is arranged to move a limited amount by said attraction to said plate, and a latch to releasably secure said poppet to said housing in response to said movement of said magnet. 6. The pulser apparatus of claim 1 wherein said poppet is attached to an acceleration compensator that responds to acceleration of said housing to apply such forces to said poppet that it will be accelerated in about the same direction and with about the same magnitude as said housing. 7. The pulser apparatus of claim 1 wherein said poppet is fitted with a pulse amplitude regulator which, in response to said pulse amplitude, limits said pulse amplitude by shortening said poppet. 8. The pulser apparatus of claim 7 wherein said pulse amplitude regulator maintains a preselected minimum pressure differential across said orifice by lengthening said poppet in response to said pressure differential across said orifice. 9. The pulser apparatus of claim 2 wherein said housing has a mud powered motor with an inlet to receive mud from the mud stream outside the housing and a discharge channel to pass mud to said downstream side of said orifice by way of said bore in said poppet, said mud motor having an output shaft to provide power to apparatus in said housing. 10. The pulser apparatus of claim 9 wherein an electric energy generator is arranged to be driven by said mud motor, said electric energy generator arranged to deliver electric power to said apparatus. 11. The pulser apparatus of claim 1 wherein said housing is, functionally, composed of surfaces in the material making up the serial drill string element carrying out the MWD function. 12. The pulser apparatus of claim 1 wherein said poppet bore is used as a passage for at least one communication conductor to pass from upstream of the pulser to drill string bore areas down stream of the pulser. 13. The pulser apparatus of claim 12 wherein said communication conductor includes a torque tube to transmit rotational information form upstream of said pulser to a location downstream of said pulser. 14. The pulser apparatus of claim 12 wherein said communication conductor carries at least one electrical conductor from upstream of said pulser to a location down stream of said pulser. 15. A pulser for use in Measurement While Drilling (MWD) in wells, situated down hole on drill strings, to generate signal pressure pulses, in response to a sensing and control instrument, in the mud stream moving down the bore of the drill string, the pulser comprising: a signal valve, comprising an orifice and a cooperating poppet with a generally cental bore extending axially therethrough, a piston on the poppet with opposing faces exposed to mud pressure communicated from the opposite sides of the orifice, arranged such that the pressure difference across said orifice tends to move said poppet away from said orifice, a spring arranged to urge said poppet toward said orifice, and a poppet position controller intermittently secured to said poppet, responsive to said instrument, to restrain the poppet in at least one position relative to said orifice, and a generally central bore extending through the poppet and said poppet position controller, said generally central bore capable of accepting a communication conductor extending axially through said pulser during pulse generating processes. 16. A pulser apparatus for use in wells, in a pipe string, to generate brief pressure changes in a mud stream flowing down the pipe string bore, in response to a down hole instrument, to convey information from the lower end of the pipe string to the surface, the apparatus comprising: a) a housing arranged for selected location in a muleshoe located in the bore of said pipe string; b) an orifice, having an upstream side and a downstream side, situated in the bore of said pipe string through which at least part of said mud stream flows; c) a poppet situated in said housing and arranged to cooperate with said orifice to comprise a signal valve to vary the resistance to the flow of said mud stream to vary the pressure drop across said orifice; d) a first piston surface on said poppet and an opposed second piston surface on said poppet; e) a first fluid pressure conducting channel arranged to conduct fluid pressure from the downstream side of said orifice to said first piston surface; f) a second fluid pressure conducting channel arranged to conduct fluid pressure from the upstream side of said orifice to said second piston surface; g) a poppet position controller, intermittently secured to said poppet, responsive to said instrument, to determine at least one controlled position of said poppet relative to said orifice; h) a spring arranged to urge said poppet toward said orifice; i) said piston surfaces and said spring so arranged that said poppet is urged toward said orifice when said pressure drop across said orifice is less than a preselected amount and is urged away from said orifice when said pressure drop across said orifice is more than said preselected amount j) said orifice situated to pass a mud stream through the wall of said drill string to generate a negative pressure pulse in response to movement of said poppet.