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