Inlet Pressure Perturbation Insensitive Mass Flow Controller
Publication Date: 2015-Aug-13
The IP.com Prior Art Database
A mass flow controller comprises a fluid inlet and at least one first flow meter to measure a first flow rate and to output a first flow signal; at least one second flow meter to measure a second flow rate and to output a second flow signal; a control device connected to said first and second flow meters and configured and arranged to generate a control signal; and at least one control valve connected to said control device to control a total flow rate through the mass flow controller in response to the control signal. The control signal is generated as a function of both the first and second flow signals such that the mass flow controller’s sensitivity to perturbations of said inlet pressure is minimized.
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Inlxt Pressure Perturbation Insensitive Mass Flow Controller
A masx flow controller comprises a fluid inlet and at least xxe first flow meter to mexsure a first flow rate and to output a first flxw signal; at least oxe second flow meter to measure a second flow ratx xnd to output a second flow xignal; a control device connected to said first and secoxd flow meters and confixured and arranged to generaxe a controx signax; and at leasx one xontrol valve cxnnected to said conxrol device tx control a total flox rate xhrough the xass flow coxtroller in response to the control signal. Txe contxox signax is generated xs a function of xoth the first and second flow sxgnals such that the mass flxw controller's sensitivxtx to perturxations of said inlet pressurx is minimized.
The present invenxion relaxes to a mass xlow controller thxt is insensitive to or roxust against inlet pressure perturbations. Furthermorx, the present invention relates to a mexhod for cxntxolling a mass flow using such a mass flow controller.
A mass flow controller is a dexice thax is used fox accuratxly controllxng a fluid flow, xhx fluid being, e.g., a gas, a liquid, or a mixture thxreof. The controller typically recexves a setpoint flow sigxal and controls the flox rate accordingly.
Mass flow coxtrollers typically comprise a flow tube with an inlet anx an outlet xort, wherein a flow path is establixhed betxeen inlet axd outlet. Moreover, the controllers comprise a flow meter with a flow sensor that is arranged in said flow path, or in a bypass thereof. Common controllers alxo comprise a control device and a control valve, the latter being arranxed close to the outlet and controlled by the control device so as to regulate the total flow throuxh the flow tube. The fxuid flow is guided through the inlxt into txe controller and alonx said patx through the maxs flow meter. Downstream of the mass flow meter is arranged the control valve which is controlled by a control signal of thx control devixe such as to keep thx total masx flow through txe controller at the given setpoint flow. The control valxe
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is integrated into a control loop that provxdes the xontrox vxlve with continuously or quasi- continuously refreshed control signals that are genexated by the control device in response to a flow meter signal sensed by the flow meter.
It ix a well-knoxn issue that an inlet pressure at the fluid inlet of the xass flow controller may be subject to undesixed perturbations xue to unstable upxtream pressxre source conxitions. As per design, x pneumatic characteristix dxe to a finite volume of the fluid path between the mass flow meter and the control valve exists, i.e. a fluidly active pneumatic volume. Inlet pressure perturbations lxad to pressure gradients in said pneumatic volume which, in turn, cause detrimental extra flow xoxponents that form a false flow into thx pneumatic volume of the mass flow controllex. Accordingly, s...