Predictive failure monitoring system for a mass flow controller

• US 6,205,409 B1
• Filed: 06/26/1998
• Issued: 03/20/2001
• Est. Priority Date: 06/26/1998
• Status: Expired due to Fees

• Current Assignee: Advanced Micro Devices, Inc.
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Zvonar, John G.
• Primary Examiner(s): SHAH, KAMINI S
• Application Number:
  US09/105,282
• Time in Patent Office: 998 Days
• Field of Search: 702/183, 702/100, 702/45, 732/041.5, 73/11.6, 137/2, 137/486, 700/282, 700/266
• US Class Current: 702/183
• CPC Class Codes: G01F 25/00 Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence
• CPC Class Codes: Y10T 137/7759 Responsive to change in rate of fluid flow

Abstract

By monitoring the output voltage of a mass flow controller (MFC) there is no way to detect when a MFC is starting to degrade (or beginning to fail) as long as the MFC output voltage is driven to match the MFC setpoint voltage. Only when the MFC actually fails, and the MFC output voltage is unable to be driven to match the MFC setpoint voltage, is the failure detectable. A predictive failure monitoring system for a mass flow controller (MFC) is disclosed which monitors the “valve voltage” of the MFC as well as the MFC output voltage. By knowing the normal relationship between the MFC setpoint voltage and the respective valve voltage, then degradation or other changes may be noticed before the MFC actually fails, and importantly, before production material is ruined by the failing MFC. Such a real-time monitoring capability may be transparently implemented as an add-on module between the MFC and the system controller for the MFC. The add-on module may be advantageously connected between the MFC card edge connector and the system card edge socket which is normally connected to the MFC card edge connector. The module monitors, in real time, the performance of the MFC by measuring the valve voltage on the valve test point. If determined to be outside of various user-settable limits, then warnings and relay closures may be done. The module can also automatically characterize the MFC operation when known to be proper, then go into a “run” mode to monitor operation and provide indications when operation falls outside of user-settable limits.

Claims

1. An apparatus for monitoring operation of a mass flow controller (MFC) comprising:

a first interface circuit having a first input for receiving a particular setpoint signal conveyed to the MFC by a control system operably connected to the MFC, and for generating, on a first output of the first interface circuit, a first signal corresponding to the particular setpoint signal, said first interface circuit having a second input for receiving an actual valve control signal generated by the MFC in response to the particular setpoint signal, and generating, on a second output of the first interface circuit, a second signal corresponding to the actual valve control signal;

a storage circuit for providing an expected valve control signal corresponding to the particular setpoint signal received by the MFC;

a comparison circuit for comparing the second signal to the first signal to determine whether the actual valve control signal received from the MFC falls within a predetermined range of expected valve control signals corresponding to the particular setpoint signal conveyed to the MFC; and

a status interface for conveying information related to whether the actual valve control signal received from the MFC is determined to fall within the predetermined range.

2. An apparatus as in claim 1 wherein:

the status interface comprises a first indicator which is activated when the actual valve control signal falls outside a first acceptable range of expected valve control signals for more than a first predetermined number of comparisons.

3. An apparatus as in claim 2 wherein:

the status interface comprises a second indicator which is activated when the actual valve control signal falls outside a second acceptable range of expected valve control signals for more than a second predetermined number of comparisons.

4. An apparatus as in claim 1 wherein:

the status interface comprises a switch closure output terminal pair.

5. An apparatus as in claim 2 wherein:

the first indicator comprises at least one user viewable status light.

6. An apparatus as in claim 2 wherein:

the second indicator comprises at least one user viewable status light.

7. An apparatus as in claim 1 wherein:

the storage circuit comprises a lookup table for storing an expected value of the valve control signal as a function of the setpoint signal received by the MFC.

8. An apparatus as in claim 1 wherein:

the storage circuit includes an equation storage circuit, for calculating an expected value of the valve control signal as a function of the setpoint signal received by the MFC.

9. An apparatus as in claim 1 further comprising:

a user selection interface for specifying the predetermined range of expected valve control signals corresponding to the particular setpoint signal conveyed to the MFC.

10. An apparatus as in claim 1 which is self contained and insertable in-line between an MFC and a system controller.

11. An apparatus as in claim 10 wherein the apparatus is operably powered by the system controller.

12. An apparatus as in claim 10 which is operably transparent to the system controller.

13. An apparatus as in claim 1 further comprising:

a second interface circuit having a first input for receiving a first pressure signal from a sensor upstream of the MFC, and for generating, on a first output of the second interface circuit, a first signal corresponding to the first pressure signal, said second interface circuit having a second input for receiving a second pressure signal from a sensor downstream of the MFC, and generating, on a second output of the second interface circuit, a second signal corresponding to the second pressure signal.

14. An apparatus as in claim 1 wherein:

the status interface circuit includes a port for connecting to a textual display device for displaying user readable status information descriptive of operational status of the MFC.

15. An apparatus as in claim 1 wherein:

the storage circuit is a portion of a larger circuit which includes a controller circuit for orchestrating operation of the apparatus.

16. An apparatus for monitoring operation of a mass flow controller (MFC) comprising:

means for comparing, in response to a particular setpoint value received by the MFC from a control system, an actual valve control value generated by the MFC against a first acceptable range of expected valve control values corresponding to the particular setpoint value received by the MFC;

means for generating a first status indication when the actual valve control value falls outside the first acceptable range of expected valve control values for more than a first predetermined number of comparisons.

17. An apparatus as recited in claim 16 further comprising:

means for storing a plurality of data pairs each providing an MFC setpoint value and a corresponding expected valve control value.

18. An apparatus as recited in claim 16 further comprising:

means for storing an equation from which, for each possible MFC setpoint value, a corresponding expected valve control value may be computed.

19. An apparatus as recited in claim 16 further comprising:

means for retrieving from a host when connected thereto, a plurality of potential setpoint values which may be received by the MFC and an acceptable range of expected valve control values corresponding to each potential setpoint value.

20. An apparatus as recited in claim 16 further comprising:

means for generating a second status indication when the actual valve control value falls outside a second acceptable range of expected valve control values for more than a second predetermined number of comparisons.

21. A method for monitoring operation within a mass flow controller (MFC) comprising:

comparing, in response to a particular setpoint value received by the MFC from a control system, an actual valve control value generated by the MFC against an acceptable range of expected valve control values corresponding to the particular setpoint value received by the MFC;

generating an alarm condition when the actual valve control value falls outside the acceptable range of expected valve control values for more than a threshold number of comparisons.

22. A method for monitoring operation within a mass flow controller (MFC) comprising:

comparing, in response to a particular setpoint value received by the MFC from a control system, an actual valve control value generated by the MFC against a first acceptable range of expected valve control values corresponding to the particular setpoint value received by the MFC;

generating a first status indication when the actual valve control value falls outside the first acceptable range of expected valve control values for more than a first predetermined number of comparisons.

23. A method as recited in claim 22 further comprising:

storing a plurality of data pairs each providing an MFC setpoint value and a corresponding expected valve control value.

24. A method as recited in claim 22 further comprising:

storing an equation from which, for each possible MFC setpoint value, a corresponding expected valve control value may be computed.

25. A method as recited in claim 22 further comprising:

retrieving from a host when connected thereto, a plurality of potential setpoint values which may be received by the MFC and an acceptable range of expected valve control values corresponding to each potential setpoint value.

26. A method as recited in claim 22 further comprising:

generating a second status indication when the actual valve control value falls outside a second acceptable range of expected valve control values for more than a second predetermined number of comparisons.