Blood cell analyzer with tube holder and cap piercer

An automated sample extraction apparatus for automatically withdrawing precise samples of biological fluid from vials of varying sizes sealed with pierceable caps, comprising:

• a holder for receiving and holding at least one vial having a pierceable cap sealing said vial;
• a cup for receiving the pierceable cap sealing said vial, the bottom of the cup having an aperture aligned with the pierceable cap;
• an electrically conductive needle extendable and retractable through the apertures in said cup for piercing the pierceable cap, the needle being hollow to permit a sample of fluid in said vial to be withdrawn through the needle;
• a driver for extending and retracting said needle, the driver including a circuit for extracting a precise amount of sample from the vial along a confined path, said circuit comprising said sample, which is conductive, the needle forming a first electrode of the circuit, and a second electrode located a fixed distance from the needle along said confined path so that as the sample is drawn from the vial through the needle the fluid comes in contact with the second electrode to form a closed conductive path between the needle and the second electrode, wherein completion of the conductive path indicates a precise amount of sample has been drawn and terminates extraction of fluid;
• and
• a safety switch interlocking said driver with said holder such that said driver can extend said needle through the aperture in said cap only when the vial is held by the holder.