Positive Displacement Motor Frequency Detection via Drill String Vibration

The patent utilizes mechanical vibration analysis of the drill string to directly determine rotational frequency. Vibration sensors mounted on the drill string measure vibrational motions that occur at frequencies related to the motor's rotational speed. By analyzing these vibration frequencies, the system directly identifies rotational frequency without requiring multiple computation steps or manufacturer characteristic curves, thereby improving both accuracy and simplifying the determination process.

The patent replaces the fluid-based measurement system (drilling fluid flow rate and pressure drop) with a direct mechanical vibration measurement system. Vibration sensors directly measure the mechanical vibrations of the drill string that correspond to the motor's rotational frequency. This substitution eliminates the need to rely on manufacturer characteristic curves and fluid dynamics calculations, providing accurate rotational frequency determination that is not affected by variations in downhole conditions such as fluid properties or pressure changes.

The patent employs vibration sensors that serve multiple functions: they measure vibrational motions directly related to rotational frequency, and these same sensors can detect other drill string properties. The vibration measurement approach is universally applicable regardless of the specific downhole conditions, eliminating the need for multiple specialized sensors. This multi-functional approach maintains measurement accuracy while reducing device complexity compared to deploying separate sensors for different measurement types.