Flow rate measurement system

TL;DR: In this article, a flow-rate measurement system is presented for outputting a measured value indicating the flow rate magnitude and flow direction of a fluid flowing through a prescribed main passage in which reverse flow can occur.

Abstract: This flow-rate measurement system is for outputting a measured value (Q) indicating the flow-rate magnitude and flow direction of a fluid flowing through a prescribed main passage (50) in which reverse flow can occur. The flow-rate measurement system is provided with a housing (45) that has a bypass passage (49) and is disposed in the main passage, a detection unit (46) that is disposed in the bypass passage and is for outputting a detected value (QA) corresponding to the flow-rate magnitude and flow direction of the fluid flowing through the bypass passage, and a calculation unit (47) for using the detected value to carry out calculation for outputting the measured value. The calculation unit calculates the measured value by using a loss factor (Cs, Cb) for at least one from among the main passage and bypass passage to, as necessary, correct for the delay of flow rate variation in the bypass passage in relation to flow rate variation in the main passage. In the loss factor calculation, there is a determination unit (S301) for determining whether the flow direction of the main passage, bypass passage, or both has changed, and if the determination unit determines that the flow direction has changed, a large side calculation method is used, while if the determination unit determines that the flow direction has not changed, a small side calculation method is used.