| 摘要 |
A multi-vortex flowmeter (1) includes a vortex flowmeter for measurement by volume flow rate and a thermal flowmeter for measurement by mass flow rate to selectively use the two flowmeters according to the flow rate of fluid to be measured flowing through a flow channel (13). The multi-vortex flowmeter (1) uses the mass flow rate for a switching point. In other words, the multi-vortex flowmeter (1) has the switching point of two flowmeters based on the mass flow rate. A mass flow rate Qm at the switching point in a range larger than the minimum flow rate of a vortex flowmeter and smaller than the maximum flow rate of a thermal flowmeter is determined by: Qm=K3*√P, (where, P is a pressure of the flow channel (variable), K3 is a constant determined by the area and the vortex differential pressure of the channel (13) and a constant related to the vortex differential pressure, a density at 0° C. and 1 atm, and the pressure at 1 atm). Alternatively, a volume flow rate Q at the switching point in a range larger than the minimum flow rate of a vortex flowmeter and smaller than the maximum flow rate of a thermal flowmeter is determined by: Q=K1/√P, (where, P is a pressure of the channel (variable), K1 is a constant determined by the area and the vortex differential pressure of the flow channel (13) and a constant related to the density at 0° C. and 1 atm, and the pressure at 1 atm).
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