Patent ID: 8196601

Claim:
A thermal flow sensor comprising, a first capillary tube having, a tube inlet port adapted to receive a fluid flow, and a tube outlet port adapted to eject a fluid flow, the tube inlet and outlet ports being adapted to couple to a mass flow controller main flow line across a mass flow controller bypass; a first pair of sensing elements coupled to the first capillary tube; a second capillary tube having, a substantially similar cross-sectional shape to the first capillary tube, a first end thermally coupled to one of a mass flow controller base and the first tube proximal the inlet port, the first end comprising a closed end, and a second end thermally coupled to one of the mass flow controller base and the first tube proximal the outlet port, the second end comprising a closed end; and a second pair of sensing elements substantially similar to the first pair of sensing elements, the second pair of sensing elements coupled to the second tube generally opposite of the first pair of sensing elements.