Re: SIM vs QN

marat@CC.UManitoba.CA
Wed, 15 Dec 93 14:18:38 CST

> One good reason: On the Aspect 3000, SIM does not work with
> 16 bit digitizer resolution (DR=16) --- this is related to the fact
> that
> the A3000 uses a 24-bit word in memory, and you need two 16 bit spots
> in
> memory simultaneously to run SIM mode (if my non-digital memory serves
> me right, and my math that 2*16 > 24 :) ). From local word of mouth

Couldn't they use 2 consecutive 24 bit words for this? since this is the
way the data would be stored anyway? Perhaps it is some other technical
detail related to the digitizer?

Our AM300 only has a 12 bit digitizer, and we often run in sim mode with no
problems. Dynamic range seems the same in both modes. Sometimes baseline
is flatter in sim, though.

Anyone at Bruker care to comment?

> tech support folks, SIM apparently works fine with DR=12 although this
> puts a fair number of interesting experiments needing high DR out of
> reach (e.g. nat'l abundance 13C/15N expts, looking at 1H spectra in
> H2O, etc). I wholeheartedly sympathize with your concerns, on both
> practical and theoretical grounds --- does anyone know if this has been
> cured in the more recent generations of machines/computers from
> Bruker?

Our AMX500 has a 16 bit digitizer, and we routinely use it in the
"qsim" mode, rather than "qseq". I am gradually changing out stock
parameter sets all over to "qsim". Dynamic range is the same (excellent)
in both modes.

The 2D/3D processing software allows all combinations (I think) of
detection modes in the different dimensions. eg. qsim in F2, TPPI in F1;
qseq in F2, States in F1, etc.

-- 
Kirk Marat
NMR Facility Manager
Dept of Chemistry / Prairie Regional NMR Centre
University of Manitoba, Winnipeg, MB, CANADA, R3T 2N2

... Criminal Lawyer (n): redundant term, see WEASEL