Patent ID: 8800383

Claim:
A method of monitoring flow rate of a gas in a particle sensor, said method comprising the steps of: providing a particle sensor comprising: a flow measurement orifice comprising a differential pressure sensor for measuring differential pressure across said flow measurement orifice; a critical orifice; a vacuum system for generating gas flow across said flow measurement orifice and said critical orifice; generating a flow of gas through said particle sensor by establishing a vacuum pressure at a position downstream of said critical orifice; determining a pressure drop (DPI) across said flow measurement orifice; determining atmospheric pressure (API); determining a pressure in said particle sensor (BPI) at a position that is upstream of said critical orifice; identifying a flow condition from said DPI, API and BPI values, wherein said flow condition is a flow rate error condition; and identifying said flow rate error condition as a vacuum-induced flow loss or an inlet-induced flow loss; thereby monitoring said flow rate in said particle sensor.