Chromatography Forum

We have an Agilent 5977b MSD that suddenly started reading an unbelievably low vacuum (1.00x10E-10 Torr), but not an error. These use a different vacuum ion gauge sender from the 5973 and 5975 series (Just a tubular unit with a connector (no box. It is marked with a barcode and 'FABU').

I suspect a failure of the hi-vacuum ion gauge sending sending unit. - Can anyone confirm this is the vacuum reading when they fail?

I don't know what the specific failure mode is, but that definitely looks like a faulty readback to me. There's no way that's a real vacuum readback (generally can't get lower than 10-5 Torr on those systems). The gauge is almost certainly gone. I don't think they throw up an actual error when the gauge fails, you just get the bizarrely low vac reading as you are currently seeing.

I would suspect the gauge, maybe the gauge filament is burnt out. You should be able to operate the 5977B without a hivac gauge plugged in though (I think).

Just out of curiosity, is it fitted with a turbopump or a diffusion pump?

It has a turbopump installed.

The nitrogen/water check and turbo speed are normal, so definitely a gauge readout problem.

We have a new gauge unit on the way. I just wasn't sure if there was a way to troubleshoot bad cable or gauge power supply vs. the all-in-one gauge unit by the reading.

Usually it is the cathode inside the ion gauge that is failing, the powersupply/cabeling is highly unlikely the issue.

When you get the replacement, disassemble the old ion gauge (unscrew the four screws closest to the chamber connection and pull the housing off), read the item number on the cathode and next time simply order the cathode itself.