The Tuning Fork Density (TFD) tool is a non-radioactive and compact fluid-density measurement device that utilizes the inertial response characteristics of a vibrating stainless steel tuning fork to determine the density of wellbore fluid mixtures. Operated near its natural frequency by a piezoceramic stack and control electronics, the tuning fork’s frequency and amplitude of vibration provide accurate density measurements, regardless of whether the fluid is static or flowing.