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Leica S430 Scanning Electron Microscope (view source)
Revision as of 00:58, 20 May 2014
, 00:58, 20 May 2014→Final Vacuum
* The turbomolecular pump is now a likely suspect. 1e-4 torr is only marginally better than a roughing pump can achieve. Turbopumps should drop the pressure into the e-6 range. It is possible the pump is not running at full speed. This should be investigated via the pump controller.
* The turbomolecular pump is now a likely suspect. 1e-4 torr is only marginally better than a roughing pump can achieve. Turbopumps should drop the pressure into the e-6 range. It is possible the pump is not running at full speed. This should be investigated via the pump controller.
* Applying light finger pressure to the air admit solenoid causes the chamber pressure to drop from 9.3e-5 torr to as much as 9.0e-5 torr; releasing it causes it to return to the starting value. This is repeatable. It suggests a possible leak related to the air admit solenoid.
* Applying light finger pressure to the air admit solenoid causes the chamber pressure to drop from 9.3e-5 torr to as much as 9.0e-5 torr; releasing it causes it to return to the starting value. This is repeatable. It suggests a possible leak related to the air admit solenoid.
After removing the Penning gauge, cleaning the O ring of residual black sand grit, and reassembling, pressures in the 9e-5 torr range can be achieved. Attention turned to the Edwards EXT120E turbomolecular pump controller. This has an analog output from 0-5 V proportional to pump speed on pins 16 and 17. (Polarity appears backwards from what the manual states.) I measured 4.955V, corresponding to the pump running at 99.1% speed. Thoughts:
* It is therefore very unlikely that we have bad bearings causing the pump not to run at full speed.
* Tightening the Penning gauge did produce a change in vacuum of around 5%. However merely rotating the magnets, which are in an external sleeve, changes the vacuum too. It looks unlikely to be a leak in the gauge. Rather, the gauge seems to be very dependent on physical orientation, even though, if left alone, the results are now very stable.
* Pushing the pump around when running did not produce a change in vacuum.
* Pushing around the solenoid valve did produce a change in vacuum.
* One of the bolts holding the solenoid on was loose. Tightening it didn't seem to be the fix.
* It is likely the solenoid valve leaking. Replacing the solenoid valve with a rubber stopper is the next step to troubleshoot the problem.
=== Image Processor board loses communications ===
=== Image Processor board loses communications ===