Paradoxical foreline pressure status on 5975C

[cbps]

Hi all,

Having a heck of a time today with what should be routine maintenance. This morning my colleague and I initially set out to replace the entire column in our 7890A. After cooling down the oven, MS interface, and inlet we initiated the vent process through the ChemStation software. Before we got to the point of turning the vent valve knob we actually decided we were NOT going to replace the column, thus we never removed the other end from the MS interface (hence negating the need to complete the vent process, or so I thought). After securing the column in the inlet we initiated the pump down process through the ChemStation software, whereupon my problems start: the foreline pressure reads a steady ~60 torr (NOT mtorr) after an hour of pumping down, and despite this high value, the status column to the right of the value reads 'pressure ok.' HUH?

Additionally, the diffusion pump heater reads as 'on', however its temperature still reads as 'cold.' As expected, the quad and MS source won't heat to their setpoints until the pump reads as hot. I checked the diffusion pump oil; it looks clear, colorless, and rests at the 'hot' level in the gauge.

Could this paradoxical status be hiding a major deficiency in my foreline pump? Is my diffusion pump temperature sensor on the fritz? Does Agilent really mean mtorr instead of 'torr'? Should I go home, grab a cup of tea, get some shuteye, and hope everything will be okay in the morning?

Any ideas would be helpful and most certainly appreciated! Thanks so much!

[LCbob]

hi

Does sound a bit weird. I would vent it and power cycle everything to start. In general the diff pump will not start until the foreline pump has got the system down to about 300mTorr, so what you have is a bit strange. On start up check the foreline pressure is going down ok, if not check the usual areas ( side plate, vent screw, column connections ).
Any issues let us know.

[Yama001]

I find I cannot trust the software for vent/pump down on the 5975C. I usually quit the software and use the front panel for those purposes. With your system in the current state, I would bet you can exit the software, restart it, and you will find your system ready to go (aside from heating the source and quads up).

[cbps]

It's certainly looking like I won't be able to trust the software for things like this in the future either.

Upon closer inspection the front panel on the MSD reads 60 mTorr, so it seems this is most likely a software glitch. Additionally, merely restarting the software resolved the 'cold' status issue, whereupon quads and source heat to setpoints and everything is good to go. The software still posts the foreline pressure at 60 torr (with 'pressure ok' status), but it certainly looks like this isn't going to be causing problems, unless someone comes along and doesn't see the note I left and freaks out at the high value as I had last night.

Thanks to all of you! I'll keep this thread updated with further complications (if any) for someone who finds themselves in a similar situation.

[MSCHemist]

I had the same bloody thing in March when I bought a 6890/5973. The chemist there called me frustrated as heck because she couldn't get the instrument to pump down. After an hour or so checking everything I tried to pump it down and it still wouldn't. Then I notice the foreline pressure on the MSD instrument screen is 70 mTorr and on Chemstation on the PC it says 70 Torr. I call Agilent and it pumps right down from the MSD controls with Chemstation closed. They said they have cateloged the problem with E.02.02 and will fix it with the next service pack.

Another oddity with E.02.02 is when I pump my 6890-5975b down from chemstation the High_vac sensor will not come on automatically as it should and I have to cycle it manually from the tuning and vacuum control menu.

[James_Ball]

I had the same bloody thing in March when I bought a 6890/5973. The chemist there called me frustrated as heck because she couldn't get the instrument to pump down. After an hour or so checking everything I tried to pump it down and it still wouldn't. Then I notice the foreline pressure on the MSD instrument screen is 70 mTorr and on Chemstation on the PC it says 70 Torr. I call Agilent and it pumps right down from the MSD controls with Chemstation closed. They said they have cateloged the problem with E.02.02 and will fix it with the next service pack.

Another oddity with E.02.02 is when I pump my 6890-5975b down from chemstation the High_vac sensor will not come on automatically as it should and I have to cycle it manually from the tuning and vacuum control menu.

I have a very early 5973 that was upgraded from HPIB to LAN which has not front display and uses a diffusion pump. I had very similar problems, the diffusion pump not giving the at temp signal soon enough and the system entering shutdown before it finished pumpdown yet the vacuum reading was showing it was ready. It also shows the high vacuum as turbo speed instead of as a diffusion pump. It is running the E.02.02 software.

What I have found is that if you turn on the MS and let it set for about 30 minutes and it is good and pumped down, then start MSChemstation it reads the vacuum as being ready and works perfectly. Just another bug in the newer versions I guess.