Turbo siren signal generator for measurement while drilling systems

Abstract

A self-propelled turbo siren modulator assembly is disclosed for use in an MWD system. The turbo siren includes a fixed turbine deflector located upstream from a rotor, which in turn is located upstream from a fixed stator. Drilling mud flowing through the turbine deflector causes the rotor to rotate independent of any external drive device. The rotor and stator preferably have a similar configuration, which includes at least one lobe and at least one port so that the rotor alternatively blocks or permits mud flow through the port(s) of the stator to create a cyclical acoustic wave signal, with a frequency that depends upon the number of lobes on the rotor and the velocity of the drilling mud. Encoded measurement data is modulated on the carrier frequency wave through the use of amplitude modulation, frequency modulation or phase shift modulation, or a combination thereof to maximize data rates. In addition, a plurality of modulator assemblies may be provided, each of which includes a different number of lobes so as to operate at different, distinct frequencies to create a plurality of transmission channels in the drilling mud medium. These plurality of modulator assemblies therefore provide a plurality of separate carrier frequency signals on which data may be modulated to increase the rate at which data is transmitted to the surface of the well.