epc oscillation

[chromtech]

I have a 5890 series 2 that has been upgraded with an epc system. With the purge valve off it controls column head pressure fine. When the valve is opened for split injection the pressure oscillates above and below the set point. Is this a symtom of an eprom mismatch?

col. head pres: 12.6
split flow: 120ml/min

[Peter Apps]

Check that the pressure feeding the GC is high enough, and that there are no restrictions in the lines.

Peter

[chromtech]

carrier pres. is @85 psi to the gc regulator, no kinks or obstructions.

[bhuvfe]

what is the spread of the oscillation?

Maybe check for leaks at the inlet (starting from the septum).

[Peter Apps]

If you have a trap between the inlet and the back pressure regulator (I am assuming that you have the usual kind of plumbing for a split splitless inlet) it may be blocked or significantly restricted.

Peter

[chromtech]

I have been all over the gc with a sniffer, can't find any leaks. Also the oscillation doesn't seem to start until the instrument is connected via HPIB to chemstation software. There is no trap, don't ask me why.

Thanks for any help in this forum, it is greatly appreciated

[Peter Apps]

Check that all the settings in Chemstation match reality; column dimensions, carrier gas, pressure units, septum purge flow and anything else that I have forgotten. Also it can't do any harm to measure the actual flows with an independent flow meter.

Peter

[chromtech]

after substition found that the septum purge regulator was faulty.

thanks again

[Peter Apps]

Thanks for the feedback

Peter