Frequency regulation of an oscillator for use in MWD transmission

DETAILED DESCRIPTION The present invention addresses these and other drawbacks in the art by creating an oscillating pressure using a control valve that is driven by the pressures in a mud pulser.
The present invention is adaptable to the mud pulser whether the drive means for operation of the pulser is upstream or downstream from the orifice, or whether or not the drive means and the poppet are on the same side or opposite sides of the orifice.
The invention comprises a toggling or bistable valve and an optional pilot valve bypass port which is inserted in the flow path of the drive fluid of such a pulser and preferably forms one wall of the drive piston of the pulser.
In this disclosure, the terms "toggling" and "bistable" are used interchangeably to refer to the valve described herein that moves quickly between open and shut and between shut and open, to effect the function herein described.
Pressure from the drive cylinder behind the drive piston is directed in such a way as to unseat the bistable valve.
When the bistable valve becomes upset it changes state, in the case of unseating the valve, pressure is bled from within the drive cylinder, this also bleeds the pressure that upset the bistable valve in the first place.
When pressure drops, then bistable valve returns to the pre-upset condition, and the cycle repeats as long as pressure is being ported to the cylinder, thereby creating a pressure oscillation, a tone, in the drilling fluid.
The bistable valve includes a pair of adjustable biasing means, preferably springs.
Adjusting the steady state tension on the biasing means alters the amplitude of the pressure developed by the bistable a valve.
Adjusting the volumetric flow rate through the valve alters the tone of the oscillation.
This way, higher or lower drilling fluid flow rates can be accommodated, and a pressure oscillation, or tone, can be developed that can be detected on the surface, regardless of drilling fluid flow rate.
The present invention reduces the poppet force and stroke required of the poppet, thereby reducing the size, cost, and weight or the MWD tool