GAS-PANEL SYSTEM
The invention involves the introduction of a gas-flow restrictor and reservoir upstream of a mass flow controller (MFC) in a gas-panel stick. The restrictor and reservoir components function to smooth out pressure spikes in the gas line, thus preventing gas-flow irregularities that can occur in an MFC or pressure-insensitive MFC. The restrictor and reservoir components can be integrated into the MFC.
1 . In a gas stick having, in an upstream-to-downstream direction, a gas-inlet line which receives gas from a gas source, a mass-flow controller connected to the gas-inlet line for receiving gas therefrom and which functions to control the rate of gas flow through the stick, and a gas-outlet line connected to the mass flow controller for receiving gas therefrom, an improvement comprising
a gas-flow restrictor placed in the gas-inlet line for restricting the rate of gas flow through the gas-inlet line to a rate substantially less than that of the gas-inlet line itself, in the absence of the restrictor, and
a gas reservoir placed in the gas-inlet line, between said restrictor and the mass flow controller, for holding a volume of gas that substantially greater than the volume provided by the gas-inlet tube itself between the restrictor and mass flow controller in the absence of the reservoir,
wherein the flow-restrictor and reservoir act to substantially reduce or eliminate gas-pressure fluctuations observed in the gas-outlet line due to fluctuations in the gas-inlet line, upstream of the gas-flow restrictor.
2 . The improvement of claim 1 , wherein the mass flow controller can be set to a selected set point for gas flow rate, and the gas-flow restrictor permits a gas flow rate through the gas-inlet line that is at least as great as the set point.
3 . The improvement of claim 2 , wherein the gas-flow restrictor restricts gas flow through the gas-inlet line to a selected flow rate between 5 and 500 standard cubic centimeter per minute (sccm).
4 . The improvement of claim 3 , wherein the gas-flow restrictor has an orifice size of between 25-30 mils.
5 . The improvement of claim 1 , wherein the gas-flow reservoir has a selected volume of between about 5-50 cubic centimeters (cc).
6 . The improvement of claim 5 , wherein the volume of the reservoir is between 10-20 cc.
7 . The improvement of claim 6 , which is effective to substantially eliminate pressure fluctuations observed in the gas-outlet line in response to gas fluctuations of between 20-25 psi in the gas-inlet line, upstream of the gas-flow restrictor, where the mass flow controller is set to a selected set point between 20 and 100 sccm.
8 . The improvement of claim 6 , wherein the gas-flow restrictor has an orifice size of between 25-30 mils.
9 . The improvement of claim 1 , wherein the mass flow controller in the stick is a pressure-insensitive mass flow controller.
10 . The improvement of claim 1 , wherein the stick also includes and filter and valve in the gas-inlet line for filtering and valving gas from the source, upstream of the restrictor.
11 . The improvement of claim 1 , wherein the gas-flow restrictor and reservoir are integrated into the mass flow controller, upstream of standard gas-flow components of the controller.
12 . The improvement of claim 1 , wherein the wherein the flow-restrictor and reservoir act to substantially reduce or eliminate gas-pressure fluctuations observed in the gas-outlet line that occur over time periods of about 100 msec or less and/or involve pressure changes of greater than about 5 psi/sec.
13 . A mass flow controller comprising, in an upstream-to-downstream direction, an inlet adapted to be connected to a gas-inlet line, a gas-flow restrictor, a gas reservoir, a mass flow sensor, a proportional control valve, and a closed loop control system that functions to compare the value from the mass flow sensor and adjust the proportional control valve accordingly to achieve the required flow, wherein the flow-restrictor and reservoir act to substantially reduce or eliminate gas-pressure fluctuations observed at the proportional control valve due to fluctuations in the gas-inlet line.
14 . The mass flow controller of claim 13 , wherein the gas-flow restrictor restricts gas flow to a selected flow rate between 5 and 500 standard cubic centimeter per minute (sccm).
15 . The mass flow controller of claim 13 , wherein the gas-flow restrictor has an orifice size of between 25-30 mils.