Experiment 9

Conductance

 

Objective: Experimentally determine the effect of a conductance limitation on a high vacuum pump.

Reference: Modules 3, 10

Required Materials:

Varian Vacuum Trainer

Stopwatch

Latex gloves

Conflat plate with a drilled 1/4 in diameter hole

(Varian Part Number FG0275CUB)

 

Experimental Procedure:

Students must wear latex gloves when handling vacuum components.

1. Install the conflat plate at the base plate mounting flange.

2. Insure that the system has achieved equilibrium at atmospheric pressure. With all valves closed, remove the bell jar and let stand for at least 15 minutes.

3. Visually inspect the base plate and gasket for cleanliness. If the gasket needs cleaning, wipe with alcohol. Dry thoroughly with a lint-free cloth and lubricate with a thin film of vacuum grease.

4. Place the bell jar and shield on the baseplate.

5. Close all valves.

6. Plug the traineer into the power outlet.

7. Turn both Mechanical and Turbo Pump toggle switches to the ON position.

8. Select the roughing gauge on the controller (TC1, Channel 1).

9. Check the gauge. It should be reading atmospheric pressure (7.6 on the +2 scale). Note: The TC gauge is not accurate above 1 Torr.

10. Open the foreline valve.

11. Press START on the Turbo Controller Panel. Allow the Turbo Controller to come up to speed ( 75 K rpm) and indicate NORMAL OPERATION.

12. Close the foreline valve.

13. Open the roughing valve in one continuous motion. Start the stopwatch as you begin opening the valve. Note: The foreline and roughing valve should never be opened at the same time.

14. Record the pressure at 30 second intervals for 5 minutes, the 1 minute intervals for the next 5 minutes until reading 3 Torr.

15. At 3 Torr, begin crossover operation by

- closing the roughing valve

- opening the foreline valve and waiting 10 seconds

- opening the high vacuum valve

16. Switch the gauge to BA (ION gauge). The gauge will begin operation when in range (<1 mtorr).

17. Continue taking readings until reaching base pressure. Record the pressure at 30 second intervals for 5 minutes, at 1 minute intervals for the next 5 minutes, and 2 minute intervals until completion. (Minimum length of the experiment is 20 minutes.)

18. Plot pressure versus time on seven-cycle x 70 division semilog graph paper.