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Measuring the performance of flow controllers used in on-site chemical mixing
- 1. Measuring the performance of flow controllers used in on-site chemical mixing Gary Van Schooneveld and Don Grant CT Associates, Inc. Eden Prairie, MN 55344 February 14, 2006
- 2. Introduction Some of the chemicals used in semiconductor processing degrade relatively quickly after they are prepared. These solutions are often prepared on-site and used shortly after preparation. Both on-line and batch mixing can be performed. Flow controllers can be used in both approaches. To prepare accurate blends, flow controllers must provide flow rates that are accurate, repeatable, reproducible, and stable. In addition, the controllers must respond quickly to set point and liquid pressure changes. Testing is required to ensure that controllers meet the required specifications. This presentation describes a test method developed to accurately measure flow controller performance and shows examples comparing flow controllers in different chemicals.
- 3. Outline Performance definitions. Test method description. Controller comparison in high purity water. The effect of temperature on controller performance. The effect of chemical type on controller performance Summary
- 4. Performance definitions Response Time: The time required to intersect acceptable control limits after receiving a new set point. Control Time: The time required to maintain acceptable control limits after receiving a new set point.
- 5. Performance definitions (2) Accuracy: Difference between the average measured flow rate (the control point) and the set point. Stability: The flow rate variability during steady-state conditions.油油油油油油
- 6. Performance definitions (3) Settling time: The time required to return flow control to acceptable limits after a perturbation in the upstream pressure. Overshoot: The extent to which the flow deviates from the desired set point following a set point change or a pressure perturbation. In the case of a set point change the overshoot is the extent to which the flow rate surpasses the new set point after initially intersecting the new set point.
- 7. Performance definitions (4) Repeatability: The range of accuracies for a device subjected to multiple identical tests. Reproducibility: The range of accuracies for several devices subjected to multiple identical tests.
- 8. Test system hydraulic schematic
- 9. Typical test procedures Test for accuracy, repeatability, stability, and reproducibility Controllers are operated with the following sequence of set points: 0, 10, 20, 30, 50, 75, 100, 75, 30, 20, 10, 0, 10, 20, 30, 50, 75, 100, 75, 50, 30, 20, 10, 0% full scale (FS) The set point changes are made at 22 second intervals Response time, control time and set point overshoot Controllers are cycled between 25% FS and 100% FS at 22 second intervals. The cycle is repeated three times Settling time and pressure change overshoot The pressure is cycled between 2 values at 20 second intervals The pressures are typically 50 and 15 psig. 4 controllers are subjected to each test
- 10. Test system response to a pressure change command Pressure increase from 15 to 50 psig. Pressure decrease from 50 to 15 psig.
- 11. Test system control and measurement capabilities
- 12. Examples of controller response to a set point change
- 13. Examples of controller accuracies
- 14. Examples of controller repeatabilities
- 15. Example of controller stabilities
- 16. Examples of controller response to a sudden pressure increase Controller 1 Controller 2
- 17. Examples of controller accuracies at different temperatures Controller 1 Controller 2
- 18. Example of the effect of chemical type on controller accuracy
- 19. Summary and conclusions Test methodology has been developed to measure the performance characteristics of liquid flow controllers. The methodology allows measurement of controller accuracy, repeatability, stability, reproducibility, response time, control time, settling time, and overshoot. Commercially-available flow controllers have widely varying performance characteristics. Temperature and liquid physical properties can have a significant effect on controller performance. Controllers should be thoroughly tested under simulated use conditions to ensure acceptable performance.