Patent ID: 11914407
Assignee: FUJIKIN INCORPORATED
Field: Measurement (Instruments)
Classification: CPC G  Y | IPC G

Claim 0:
1. A flow rate control method comprising:
providing:
a control valve;
a restriction part provided downstream of the control valve;
a differential pressure sensor for directly measuring a differential pressure between the upstream side and the downstream side of the restriction part;
a downstream pressure sensor for measuring an absolute pressure downstream of the restriction part, the downstream pressure sensor being independent of the differential pressure sensor; and
an arithmetic control circuit connected to the control valve, the differential pressure sensor, and the downstream pressure sensor,
wherein the differential pressure sensor includes:
a primary-side connection member communicating with a flow path upstream of the restriction part;
a secondary-side connection member communicating with a flow path downstream of the restriction part; and
a sensor body connected to the primary-side connection member and the secondary-side connection member, the sensor body having a built-in sensor chip for measuring the differential pressure, and
the arithmetic control circuit is configured to perform a differential pressure control or a proportional control of the control valve based on the output of the differential pressure sensor and the output of the downstream pressure sensor,
determining an arithmetic flow rate in the differential pressure control according to an equation that Qc=K2·P2m·ΔPn or Qc=C1·(ΔP+P2)/√T·((P2/(ΔP+P2))m−(P2/(ΔP+P2))n)1/2, where Qc is the arithmetic flow rate, ΔP is the differential pressure output by the differential pressure sensor, P2 is the downstream pressure output by the downstream pressure sensor, K2 is the proportional coefficient depending on the fluid species and fluid temperature, m and n are constants derived from the actual flow rate, C1 is the coefficient including the orifice cross-sectional area, T is the gas temperature,

determining an arithmetic flow rate in the proportional control by an equation that Qc=K1·(ΔP+P2), where Qc is the arithmetic flow rate and K1 is a proportional coefficient depending on a fluid species and a fluid temperature,
controlling the control valve so that the arithmetic flow rate becomes the set flow rate in the differential pressure control and the proportional control, and
calibrating zero-point drift of the differential pressure sensor before determining the arithmetic flow rate under a condition where a pressure of an upstream side of the differential pressure sensor and a pressure of a downstream side of the differential pressure sensor are the same.