Previously, I have discussed the cryotorr 8, but how does it work?
A small presentation is shown at the helix website. The cryo-pump uses helium as cooling agent. It cryo-condenses water, nitrogen and argon by frosting them on the condensation array. By using activated charcoal, it cryo-adsorbs hydrogen, helium and neon. Water is cryo-condensed on the first stage array, at ~65K. Nitrogen and argon are cryo-condensed on the second stage at ~12K. Hydrogen, helium and neon are cryo-adsorbed also on the second stage.
By cryo-pumping, we are able to lower the pressure to ~3e-11 Torr from 8e-11 Torr.
Sunday, November 06, 2011
Thursday, November 03, 2011
If there is no gas load, what is the lowest of the cryotorr 8 cryo-pump?
Following the previous post, you have installed a new cryo pump cryotorr 8 from Brooks Automation, P/N 8033170. However, the lowest temperature you get after the bake is ~13K, which is almost the same you've reached with the previous cryo-pump.
Shouldn't be lower?
Talking to the technical support, GUTS, the cryo-pump temperature of the second stage should be ~11K. However, it could be easily 1K off and even up to 2K because the silicon diode thermometer is not calibrated. There is no clear-cut reason for a ~13K reading instead of ~11K. It could be due to the calibration curve, or it could be due to a tiny leak. I strongly recommend you to rule out the last possibility by performing an extensive leak-check.
In the case of the second option, where you do not have a calibration curve for the thermometer, it is important how you read the temperature. Brooks automation recommends using a Brooks temperature indicator, P/N 8043459G001; it comes with a "standard" calibration curve. If you are using a Lakeshore 211 temperature controller, it has three different standard calibration curves corresponding to dt470, dt670 and CTI silicon diodes. You can test the display reading of a Brooks temperature indicator against the Lakeshore 211; when the Lakeshore 211 using the CTI calibration curve displays 13.4K, the Brooks temperature indicator will display 12.9K.
Shouldn't be lower?
Talking to the technical support, GUTS, the cryo-pump temperature of the second stage should be ~11K. However, it could be easily 1K off and even up to 2K because the silicon diode thermometer is not calibrated. There is no clear-cut reason for a ~13K reading instead of ~11K. It could be due to the calibration curve, or it could be due to a tiny leak. I strongly recommend you to rule out the last possibility by performing an extensive leak-check.
In the case of the second option, where you do not have a calibration curve for the thermometer, it is important how you read the temperature. Brooks automation recommends using a Brooks temperature indicator, P/N 8043459G001; it comes with a "standard" calibration curve. If you are using a Lakeshore 211 temperature controller, it has three different standard calibration curves corresponding to dt470, dt670 and CTI silicon diodes. You can test the display reading of a Brooks temperature indicator against the Lakeshore 211; when the Lakeshore 211 using the CTI calibration curve displays 13.4K, the Brooks temperature indicator will display 12.9K.
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