As always many thanks to all those who replied to my question about air
dryers and how they affect NMR signals.
The problem I was having with a fluctuating lock signal correlated to
the cycle time of my desiccant air dryer has been observed by many of
you. The solution to the problem is to insert a ballast tank between
the output of the air dryer and the input to the supply air for the
spectrometer, the larger the tank the better. I found a 2 litre tank
kicking around our department and installed it. This eliminated the
problem. Those whose air dryers are far removed from the instrument may
not need to install such a tank as the volume of the air lines may be
large enough dampen the effect.
Thanks again.
Glenn Facey
__________________Here is my original post ____________
I have just installed a FTS AD-80 air drier with FTS AF-6 flow
regulator in my lab. The dry air is passed through a regulator and
used as the input for the "supply" air for a Varian INOVA 500
console used for spinning, bearing and VT gas. The VT gas (both
high and low) is sent through an FTS chiller and temperature
controller (supplied by Varian). Every 30 seconds when the AD-80
air drier cycles between desiccant columns, it make a loud hiss
(which is normal) however the 2H lock signal drops detectably every
time the unit cycles. This (of course) will adversely affect my NMR
measurements. I know that many of you have installed such
systems in your labs. Have you seen the same problem? Do I
have to install a buffer tank?
Here are pressures and flow rates I use:
Input to AD-80 = 80 psi
output from AF6 = 45 psi (as recommended by FTS)
output from regulator, input to "supply" = 30 psi
vt flow meter = 15 L/min
Glenn A. Facey, Ph.D.
NMR Facility Manager
University of Ottawa
mailto:gafacey_at_science.uottawa.ca
http://www.science.uottawa.ca/~nmr
Received on Mon Jun 28 2004 - 08:21:25 MST