US Patent 7866209 Fluid level regulator

A biological specimen collection and transfer system, including a biological sample container configured for storing a biological fluid sample, a vacuum source, a specimen filter having an interior chamber and an opening in communication with the chamber, and a fluid level regulator configured to determine a fluid level in the biological sample container and to dispense a fluid into the container if the determined fluid level is less than a desired fluid level. The fluid level regulator includes a fluid level monitor, a fluid dispenser, and a controller in communication with the fluid level monitor and the fluid dispenser, wherein the fluid level monitor includes a sound source configured to emit sound towards a surface of the fluid sample, and a sound detector configured to measure sound reflected from the surface of the fluid sample, wherein the controller determines the fluid level based at least in part on a measurement of reflected sound emitted from the sound source.