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3098 Technical Manual Installation Procedure
2-5
Purge Cycling
10. Close valve (C).
11. When Control Pressure Indicator is at the desired value, shut valve (A) and open valve (F). Allow the gas to vent to
atmospheric pressure.
12. Close valve (F) and open valve (A).
13. When Control Pressure Indicator is at the desired value, shut valve (A) and open valve (F). Allow the gas to vent to
atmospheric pressure.
Actions 12 and 13 define the purging cycle required for setting up the reference chamber gas in the 3098.
The number of times that this procedure should be repeated depends upon the gas regulator pressure used and is defined by:
»
¼
º
«
¬
ª
pressureregulatormax
7 x 3
=cyclespurgeofNumber
14. Once the required number of cycles has been performed, close valve (F) and open valve (A).
15. When the desired gas pressure inside the chamber has been reached (as shown by the Control Pressure Indicator)
shut the chamber valve.
DO NOT open the chamber valve again.
The gas now inside the 3098 chamber is the line reference gas.
3098 Calibration using two known gases
16. Close valve (A).
17. Connect the first calibration gas bottle to the pipework and set the pressure to be typically 25% above that inside the
reference chamber.
18. Open valve (B).
19. Ensure valve (C) is open and allow gas to flow until the time period as measured by the signal converter/flow
computer is stable to ±1ns or better (the typical stability will be better than this). [For the required electrical
connections see Chapter 3]
20. Note this time period (τ
1
) together with the certified SG from the bottle of gas (SG
1
).
21. Shut valve (B).
22. Replace the first calibration gas bottle with the second calibration gas bottle.
23. Set pressure to typically 25% above that inside the reference chamber and open valve B.
24. Allow gas to flow until the time period shown by the meter is stable to ±1ns or better.
25. Note this time period (τ
2
) and the certified SG from the bottle of gas (SG
2
).
26. Apply these noted numbers into equations (1) and (2) below:
() ()
()
(2)
(1)
2
1210
2
2
2
1
21
2
τ
ττ
KSGK
SGSG
K
−=
»
¼
º
«
¬
ª
−
−
=
Alternatives to this are to use the calibration certificate shown in table 4 (found in Chapter 4), or to use the Excel
program ‘Calcert.xls’ that is supplied on the attached floppy disk.
28. Shut valve (B) and disconnect the second calibration gas bottle from pipework.
29. Open the isolation valve (D).
30. Open valve (A).