Method and apparatus for in situ testing of gas flow controllers
Methods and apparatus utilize a rate of drop in pressure upstream of a gas flow controller (GFC) to accurately measure a rate of flow through the GFC. Measurement of the gas flow through the many gas flow controllers in production use today is enabled, without requiring any special or sophisticated pressure regulators or other special components. Various provisions ensure that none of the changes in pressure that occur during or after the measurement perturb the constant flow of gas through the GFC under test. A pressure regulator is coupled to a gas source. The GFC is positioned downstream of the pressure regulator. A pressure transducer is measuring pressure in a volume between the pressure regulator and the GFC. Techniques are provided for increasing the pressure in the volume.
1. A method to determine a volume of a first portion of a gas flow control system, the method comprising:
establishing a first pressure in the first portion of the gas flow control system;
isolating the first portion from a second portion that is of another part of the gas flow control system, wherein the volume of the second portion is known;
establishing a second pressure in the second portion of the gas flow control system;
effecting fluid communication between the first portion and the second portion of the gas flow control system;
measuring a third pressure in the gas flow control system after fluid communication is effected; and
using the first pressure, the second pressure, and the third pressure to determine a total volume of the first portion.
2. The method of claim 1 , wherein the first portion of the gas flow system is a volume that is variable.
3. The method of claim 2 , wherein the first portion of the gas flow system includes a moveable membrane for varying the volume.
4. A method to determine a volume of a first portion of a gas flow control system, wherein the downstream side of the volume is defined by a gas flow controller and the upstream side of the volume is defined by a means to interrupt the gas flow, the method comprising:
effecting fluid communication between the first portion and a second portion that is of another part of the gas flow control system, wherein the volume of the second portion is known;
establishing a flow of gas through the gas flow controller at a constant rate;
interrupting the gas flow upstream of the first portion;
measuring at a first time, a first pressure in the first portion;
measuring at a second time after the first time, a second pressure in the first portion;
determining a first rate of drop in pressure from the first pressure and the second pressure;
isolating the first portion from the second portion of the gas flow control system;
measuring at a third time, a third pressure in the first portion;
measuring at a fourth time after the third time, a fourth pressure in the first portion;
determining a second rate of drop in pressure from the third pressure and the fourth pressure; and
using the first rate of drop in pressure and the second rate of drop in pressure to determine a total volume of the first portion.
5. The method of claim 4 , wherein the first portion of the gas flow system is a volume that is variable.
6. The method of claim 5 , wherein the first portion of the gas flow system includes a moveable membrane for varying the volume.
7. A method of determining a flow rate of gas through a gas flow controller positioned downstream of a pressure regulator having a set point, the method comprising:
establishing a flow of gas through the gas flow controller at a constant rate;
increasing the pressure in a known volume, upstream of the gas flow controller but downstream of the pressure regulator, to a level above the set point of the pressure regulator;
measuring at a first time, a first pressure in the volume;
measuring at a second time after the first time, a second pressure in the volume;
determining a rate of drop in pressure from the first pressure and the second pressure; and
determining the fixed flow rate based upon the rate of pressure drop and the known volume.
8. The method of claim 7 wherein the increase in pressure is brought about by momentarily introducing a gas pressure above atmospheric pressure into the body of the pressure regulator to increase the set point.
9. The method of claim 7 wherein the increase in pressure is brought about by momentarily flowing gas from upstream of the pressure regulator to downstream of the pressure regulator.
10. The method of claim 7 , wherein the step of increasing the pressure includes opening a valve having an input coupled to a secondary gas supply and an output to the pressure regulator.
11. The method of claim 7 , wherein the step of increasing the pressure includes causing the flow of gas to bypass the pressure regulator.
12. A method of determining performance of a gas flow controller, the method comprising:
establishing a flow of gas through a gas flow controller at a constant rate;
increasing the pressure in a known volume, upstream of the gas flow controller but downstream of a pressure regulator having a set point, to a level above the set point of the pressure regulator;
measuring a first pressure drop of the known volume;
after at time period, again increasing the pressure in the known volume, upstream of the gas flow controller but downstream of the pressure regulator, to a level above the set point of the pressure regulator;
measuring a second pressure drop in the fixed volume; and
detecting drift in flow rate of the gas flow controller based upon a difference between the first pressure drop and the second pressure drop.
13. The method of claim 12 wherein the increase in pressure is brought about by momentarily introducing a gas pressure above atmospheric pressure into the body of the pressure regulator to increase the set point.
14. The method of claim 12 wherein the increase in pressure is brought about by momentarily flowing gas from upstream of the pressure regulator to downstream of the pressure regulator.
15. The method of claim 12 , wherein the step of increasing the pressure includes opening a valve having an input coupled to a secondary gas supply and an output to the pressure regulator.
16. The method of claim 12 , wherein the step of increasing the pressure includes causing the flow of gas to bypass the pressure regulator.
17. A method of determining performance of a gas flow controller, the method comprising:
establishing a flow of gas through a calibrated gas flow controller at a constant rate;
increasing the pressure in a known volume, upstream of the gas flow controller but downstream of a pressure regulator having a set point, to a level above the set point of the pressure regulator;
measuring a first pressure drop of the known volume;
substituting a gas flow controller to be tested, for the calibrated gas flow controller;
increasing the pressure in the known volume, upstream of the gas flow controller but downstream of the pressure regulator, to a level above the set point of the pressure regulator;
measuring a second pressure drop in the fixed volume; and
detecting deviation in the flow rate based upon a difference between the first pressure drop and the second pressure drop.
18. The method of claim 17 wherein the increase in pressure is brought about by momentarily introducing a gas pressure above atmospheric pressure into the body of the pressure regulator to increase the set point.
19. The method of claim 17 wherein the increase in pressure is brought about by momentarily flowing gas from upstream of the pressure regulator to downstream of the pressure regulator.
20. The method of claim 17 , wherein the step of increasing the pressure includes opening a valve having an input coupled to a secondary gas supply and an output to the pressure regulator.
21. The method of claim 17 , wherein the step of increasing the pressure includes causing the flow of gas to bypass the pressure regulator.