Vacuum Controller

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Here is some example of my work that I have done.

Here is some example of my work that I have done.

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  • 1. Originator Kris Jearakul April 11, 2003
  • 2. Objective an automatic vacuum control system for Develop engineering and production use to test the new product or an experiment that needs an accurate vacuum control system. Enable the engineer to test a product or run experiment under controlled ramp down vacuum profile. (example 760 – 100 torr in 5 minutes) Vacuum control system April 21, 2003 Page 2
  • 3. Identify Customer: Engineering and Production. Requirement: An automatic vacuum control system. CTQ: To be able to control vacuum level including ramp up and ramp down rates. Technology Gaps: - Vacuum controller - Control software Vacuum control system April 21, 2003 Page 3
  • 4. Design Key Input Vacuum controller • Controller operate range is 760 – 0 torr; • Controller accuracy should be within + 3 torr; • RS232 Serial port for remote control operation via computer. Control Software • To be able to control ramp up, ramp down or stabilize vacuum level. The control profile can be programmable. Vacuum control system April 21, 2003 Page 4
  • 5. Design controller: Vacuum Plan to buy vacuum controller from XXX company, which vendor claims to meet the requirements. Software: Control Use LabView 6.1 to create the control software. Vacuum control system April 21, 2003 Page 5
  • 6. Design Connection diagram for vacuum control system Vacuum Pump Vacuum PC with Vacuum Controller Control SW Chamber The main function The PC with vacuum of the vacuum control software is controller is to needed for adjust the vacuum programmable ramp level in the down or ramp up rate vacuum chamber of vacuum level. To to the set-point achieve the task the software will calculate the new vacuum level set-point by time frame and then send to the vacuum controller. Vacuum control system April 21, 2003 Page 6
  • 7. Design Specification from vendor Vacuum Controller: Accuracy : + 3 Torr Control Method: 0 – 100% Pulse Width modulation valve operated at 328 Hz. Resolution: 10 bits A/D (Using PIC 16F873 MCU) range 760 – 0 Torr. RS232: Operate in Talk Mode by using polling method, controller will keep sending its reading and set- point to the port. Vacuum control system April 21, 2003 Page 7
  • 8. Optimize Design Problem Original Vacuum controller Firmware : - Loop response time was too slow from vendor source code; the controller take at least 0.3 sec per loop. It would take at least 100 cycles of PWM for controller to take action when the vacuum level was changed or the set-point is changed. - Polling mode serial communication, using a bit banging technique, caused a lot of problems in designing of the software for remote computer; timing of sending has to be within the time frame when the controller executes command read from serial port. Vacuum control system April 21, 2003 Page 8
  • 9. Optimize Design Solution Vacuum controller: Rewrite the firmware for controller -Rewrite the firmware using C language instead of BASIC for more compact and speed of program. -Reduce the control loop time. Reduce A/D sampling numbers. -Program the serial port on chip of controller to be operated in interrupt mode. -Redesign the PI loop control and adding ability for user to set the gain. -Redesign the communication protocol via RS232. Modify the circuit on vacuum controller -Using the different port for LCD display to free up the TX and RX pin. -Add RS232 transceiver chip (MAX232). Vacuum control system April 21, 2003 Page 9
  • 10. Original Firmware Box Diagram Display: Vacuum Read the new set- Level, Reading and point from the Serial Set point Port within time frame Send: Vacuum and 100 ms Set-Point to RS232 Ref mode: Do nothing Off Mode: Turn all valves off Read Vacuum Level Reg Mode: Calculate PWM % 60 readings from ADC and send to vacuum valve CH0 Full Mode: Turn on 100% of Vacuum valve Vent Mode: Turn Vent Valve on Read Set-Point Read the toggle 60 readings from ADC switch from ADC CH4 CH1 Vacuum control system April 21, 2003 Page 10
  • 11. Improved Firmware Box Diagram RS232 Interrupt Display: Vacuum Read Vacuum Level Level, Reading and Handling: send the Vacuum from ADC CH0 Set point and Mode Level upon request. Update the Set-Point Check the Mode RS232 Interrupt from ADC CH1 (Local) setting either from Handling: send/receive the and RS232 (Remote) ADC CH4 (Local) or new SP upon request. RS232 (Remote) RS232 Interrupt Read the toggle Handling: send/receive the Ref mode: Do nothing switch from ADC CH4 operating mode upon Off Mode: Turn all valves off request. Reg Mode: Calculate PWM % and send to vacuum valve Full Mode: Turn on 100% of Vacuum valve Will be called upon receiving a command Vent Mode: Turn Vent Valve on from Serial Port. Vacuum control system April 21, 2003 Page 11
  • 12. Hardware Change Connect TX and RX pin from MCU to MAX232 chip. Re-wiring wires from MAX232 to serial connector. Re-wiring the LCD data lines Add MAX232 serial transceiver chip. Vacuum control system April 21, 2003 Page 12
  • 13. Vacuum control software System Requirement: PC with Com port RAM 64 MB Minimum OS: Windows 98SE or higher and have NI-MAX installed. LabView 6.1 Run-time install Vacuum control system April 21, 2003 Page 13
  • 14. Remote Control Software Vacuum profile chart Vacuum profile Control Terminal Emulation of the controller Vacuum control system April 21, 2003 Page 14
  • 15. Vacuum Profile control’s Flowchart Start Read the setup Read the vacuum SP - Vac profile step from level from Level > file. Controller Threshold ? YES NO Change the Switch to Vent Switch to controller to Remote mode to open Regulator mode Is it the last and then switch to Ventilation if controller is in step? Reg. mode Vent mode. Valve NO YES Calculate the set Change the controller point by function of to Local mode and time, then sent to save vacuum profile. controller End Vacuum control system April 21, 2003 Page 15
  • 16. Test and Verify Objective : To verify the vacuum controller and control software is working as per CTQ . Procedure : - Create the profile file to test. - Connect vacuum controller to the vacuum chamber fixture. - Set Threshold = 20 Torr and loop time = 0.5 sec with controller gain setting = 6 and 3 . - Run the software to see what results we get. Vacuum control system April 21, 2003 Page 16
  • 17. Test Profile Setup 760.00,300.00,30.0 // Step 1 Start from 760 -> 300 by 30 seconds 300.00,300.00,10.0 // Step 2 Stabilize at 300 for 10 seconds 300.00,200.00,10.0 // Step 3 From 300 -> 200 by 20 seconds 200.00,200.00,20.0 // Step 4 Stabilize at 200 for 20 seconds 600.00,600.00,25.0 // Step 5 Jump to 600 and stabilize for 25 seconds 600.00,100.00,10.0 // Step 6 From 600 -> 100 by 10 seconds 100.00,100.00,25.0 // Step 7 Stabilize at 100 for 25 seconds 100.00,50.00,10.0 // Step 8 From 100 -> 50 by 10 seconds 50.00,50.00,10.0 // Step 9 Stabilize at 50 torr for 10 seconds 50.00,20.00,10.0 // Step 10 From 50 -> 20 within 10 seconds Profile Setup Chart 800 700 600 Vacuum Level 500 400 Set Pt 300 200 100 0 Time 8.5 17.5 26.5 35.5 44.5 53.5 62.5 71.5 80.5 89.5 98.5 107.5 116.5 125.5 134.5 143.5 152.5 Time (sec) Vacuum control system April 21, 2003 Page 17
  • 18. Results With controller gain setting = 6, the controlled vacuum profile was quite smooth but found some spiking while ramping down. Vacuum control system April 21, 2003 Page 18
  • 19. Results Controller gain setting = 3 With controller 800 gain setting = 700 3, the controlled vacuum profile is 600 very smooth, no Vacuum Level (Torr) 500 spiking noticed in Open Vent Valve the controlled Set Pt 400 Vacuum profile. 300 200 100 0 4 13 22 31 40 49 58 67 76 85 94 103 112 121 130 139 148 8.5 17.5 26.5 35.5 44.5 53.5 62.5 71.5 80.5 89.5 98.5 107.5 116.5 125.5 134.5 143.5 152.5 Time Time (sec) Vacuum control system April 21, 2003 Page 19