Patent ID: 7367241

Claim:
A differential pressure type flowmeter characterized in that flow rate measurements are performed with high accuracy over a wide flow rate range by combining a first differential pressure type flowmeter for measuring a flow rate range of 100%-10% of the maximum flow rate range and a second differential pressure type flowmeter for measuring a flow rate range of 10%-1% of the maximum flow rate range, and by switching fluid to be measured in accordance with the aforementioned flow rate ranges using a switching valve, to supply fluid to the first and second differential pressure type flowmeters, wherein one of the first and second differential pressure type flowmeters is a differential pressure type flowmeter comprising: an orifice; a detector disposed to detect fluid pressure P 1 on an upstream side of the orifice; a detector disposed to detect fluid pressure P 2 on a downstream side of the orifice; a detector disposed to detect fluid temperature T on the upstream side of the orifice; and a control computation circuit that computes a fluid's flow rate passing through the orifice with the pressure P 1 , wherein pressure P 2 and temperature T are detected by the aforementioned detectors, and the fluid's flow rate Q is computed using equation Q=C 1• P 1√ T• (( P 2 /P 1) m −( P 2/ P 1) m ) 1/2 , where C 1 is a proportional constant, and m and n are constant.