we're having a leaking H2 amp head on our 253 for a while now (seems to be the wire feed throughs for the ribbon cable, still looking for a way to reseal it w/o taking everything apart) and it definitely does affect linearity. For the time being, when we run hydrogen we have a second rough pump hooked up to it, pumping against the leak. Without pumping the standard deviations for the on/offs increase about fivefold. And that is with our ambient air typically being very dry around here.
We've had people telling us amp head vacuum wouldn't make much of a difference before. At least for our hydrogen that is not correct.
While we were looking for the leak we changed the O-ring. A weak point of the seal on some machines seem to be the four clamps tightening down the housing on the O-ring. If you can't get a new O-ring anytime soon try regreasing it a bit and potentially add two or four extra clamps from the hardware store for a better pressure distribution.
Dr. Veith Becker
Isotope Science Laboratory (ISL)
Department of Geoscience
University of Calgary
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> On Sep 6, 2019, at 3:20 , Melanie Gimpel <[log in to unmask]> wrote:
> Hi all,
> some time ago I've asked for help for my unstable MAT 253 (poor stability and no linearity). I got a lot of input of the community. Thanks a lot for it! But until now, I couldn't solve the problem.
> Embarrassingly I never had a look at the pumps. Otherwise, I would have found out, that the amplifier housing is not evacuated (knob on position "vent" instead of "HV") since we reinstalled the MAT 253. Evacuation has failed, probably due to a leaky O-ring in the amplifier housing or due to a defect pump valve? A service engineer left the IRMS in this condition and assumed that measurement will be possible without evacuation of the amplifier housing.
> Is it probable that my problems concerning the stability and linearity are caused by the amplifier housing? Has anyone experiences with this? Unfortunately it isn't easy to get a new O-ring. Otherwise, I would simply replace the O-ring.
> Best regards
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