Support
At
Doty Scientific, “commitment to service” is not an empty slogan. Years
ago it was determined that service needed top
level
direction. Indeed, our Vice President,
George Entzminger, has service as his first priority.
FAQ
(Frequently Asked Questions)
General
Information
1.
Do you have international sales or service offices?
2.
Whom can I talk to with questions about probe or coil operation or about
problems I am having?
3.
Whom should I call to Clarify Specifications on an order I have placed?
4.
What should I do if I want to send my probe or coil back for service?
5.
What information should I send with the probe?
6.
Is there anything special I should do for return of an item from outside
the United States?
7.
What is your shipping address?
8.
Do I need a Return Authorization Number?
Technical
Information / Troubleshooting
1.
What do I check if my MAS probe will not spin up to specification?
2.
I have spikes in my FID. What is causing this?
3.
What is the best procedure to use to spin an MAS rotor to avoid problems?
4.
My MRI RF coil does not have the homogeneity I expect, what
should I do?
5.
How can I spin a liquid or semi-liquid in a rotor without leaks?
6.
What turbine caps do I use for extended VT?
FAQ
General
Information
1. Do
you have international sales or service offices?
The
answer is yes. We are proud that Greg Coumbarides and Goss
Scientific have provided a European Sales and Service office
for Doty Scientific for many years. Greg has provided excellent sales
and service for our European customers.
Within
the last year, we have added an authorized service center in Germany.
Dave Cross and ROTOTEC SPINTEC will be able to help
with service of Doty products in that area.
We
have had sales representation in Japan for several years but are happy
to report that LA Systems is now providing service
as well as sales for Doty products in Japan.
Check
out our Contact Us page
for the information you need on these sales and service representatives.
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2. Whom
can I talk to with questions about probe or coil operation or about
problems I am having?
You
can call us at (803) 788-6497. If you select service from
the menu, you will probably talk to George Entzminger or
Jim Jenkins. Sometimes
Laura Holte our sales manager, or Jim Gravel, or John Staab
will help you. If you prefer
email,
service@dotynmr.com
or george@dotynmr.com .
If you need to send a fax, (803) 736-5495.
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3. Whom
should I call to Clarify Specifications on an order I have placed?
If
you have specifications you need to give us for a new order, you
can call us at (803) 788-6497. It is best to ask for Dave McCree
or John Staab, head of engineering, with specifications (but George,
Laura, or Jim will be glad to take your call as well).
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4. What
should I do if I want to send my probe or coil back for service?
First,
contact us about the problem. Call or email us with a description
of the problem. It is important to provide the name of your institute,
and the Doty probe or coil serial number. (The
serial number starts with “DSI-“ and is usually located on our probes
where shown below.) The serial number can be found on the cover
of your manual. If the probe needs to return to Doty for repair,
we will allot a RMA (return material authorization) number for
it.
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5. What
information should I send with the probe?
Enclose
a letter with the probe detailing the problem, the associated RMA number,
and contact information including a contact person and phone, email,
address. Please also send all tuning elements of the
probe back so that tuning for all nuclei can be checked during repair.
It saves time later if you also enclose the address for return of the
item after
repair.
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6. Is
there anything special I should do for return of an item from outside
the United States?
It
is important to check with your country’s customs office or your
customs broker. Sometimes there are special forms that you need
to fill out before returning an item. (It may be helpful to have
one of our international service representatives help you with
the customs, even if the probe has to come back to the United States.)
It
is very important to write on your waybill, commercial invoice and
on any other paper work: " Goods made in the United States being
returned to manufacturer for service or repair. No Duties or Taxes
are due."
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7. What
is your shipping address?
Our
shipping address is:
Doty
Scientific, Inc,
700
Clemson Rd.
Columbia,
SC 29229
USA
(if outside the US)
8. Do
I need a Return Authorization Number?
Yes,
we do require prior authorization. Please contact us for a RMA number
before shipping the probe and tuning elements to us for repair. Also,
be sure to include full contact information, Doty probe (or coil) serial
number information and a complete description of problems
on paper
in the box with the product to avoid unnecessary delays.
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Technical
Information / Troubleshooting
1. What
do I check if my MAS probe will not spin up to specification?
The
most common problem with spinning is poorly packed or balanced samples. Samples
should be finely powdered to avoid more massive lumps positioned asymmetrically
on the inside circumference of the rotor. Add the sample to the rotor
as evenly as possible and then spin the sample slowly for a couple
of minutes to let it “spin pack” before gradually increasing the speed.
Also
fairly common with probes that have been in the field for a while is
excessive turbine cap wear. Turbine caps wear both from spinning
and handling during the loading process. The photographs below show
examples of good turbine caps and completely worn-out caps that need
to be replaced.
Good
Turbine Cap Worn-out
Turbine Cap
Much
less common but still possible in some extremes is excessive rotor
wear usually caused by spinning an unbalanced sample for a significant
period of time. This usually also causes stator wear and may require
a trip to the factory for service of the probe.
If
you try to spin an empty rotor and still have problems with a new set
of turbine caps then there may be a problem with the probe that will
require factory service.
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2. I
have spikes in my FID. What is causing this?
“Spikes” in
the FID are asynchronous noise bursts at the observe frequency being
generated somewhere in the NMR system. There are several possible
sources for this noise including arcing in the probe or sample coil. A
bad cable or poor quality cable that has recently been put into the
system could cause the problem. Devices external to the probe or
sample coil can arc causing the noise. Frequently we find that high
power filters in-line before the Doty probe or coil are the source
of troublesome noise spikes. To isolate the cause it is a good idea
to switch out parts to see if eliminating one part also eliminates
the problem. To check the Doty probe or coil for high level arcing
an inline directional coupler, which will allow you to see the reflected
pulse envelope on an oscilloscope, is very useful. If the probe
is arcing then you will see a sudden large jump in reflected power
during the pulse at the point of initiation of the arc. The probe
can be the source of the noise even if there is no high level arc visible
in the reflected pulse envelope. This noise can be caused by a defective
ground contact inside the probe and generate no other signs of arcing. If
you are convinced after checking the system that the probe is the source
of the noise then the best thing to do is send it back to us for evaluation
and repair.
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3. What
is the best procedure to use to spin an MAS rotor to avoid problems?
There
are normally instructions in the user manual for the correct method
for your probe. However, some general instructions are:
• Start
with about 10 psi of bearing gas pressure.
• Add
a couple of psi of drive pressure to get the rotor spinning.
• Gradually
increase bearing and drive together keeping bearing 10 to 15 psi higher
than drive up to about 40 psi on the bearing.
• After
this the drive can be increased faster than the bearing until the drive
is equal to or slightly greater than the bearing up to the maximum
spinning speed. This should be achievable with less than 60 psi on
both drive and bearing gas lines.
• Regardless
of the above instructions always listen carefully to the sound of the
spinner. If there is a change in pitch quality, this may indicate
that more bearing pressure is required.
The
user should be aware that there are spinning speed limits that are
different depending on the type of rotor, turbine cap and sample
being used. Never exceed the speed rating of the slowest
component in the spinner system. The speed ratings for various
components are given in the user manual and on the MAS
Spinning Speed Page .
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4.
My MRI RF coil does not have the homogeneity
I expect. What should I do?
Homogeneity
is sometimes hard to evaluate on the bench and we need to have a quantitative
indication to use. Look at the discussion on Coil
Lengths for guidelines on what typical
field profile to expect in small coils. We
recommend a spin-echo mapping method (see S. Crozier, K. Luescher,
L.K. Forbes,
and D.M. Doddrell, "Optimized Small-Bore, High-Pass Resonator
Designs," J. Magn. Reson. Ser. B , 1995, 109 ,
1-11) in which a series of slice-selective spin-echo images are acquired
with varying pre-pulse lengths. The pre-pulse lengths should be (2*n*π )
where n is 0,1,2, and possibly 3. The resulting images will have
varying degrees of inhomogeneity with rings of light and dark that
can be used to quantitatively evaluate B1. Quantitative
B1 mapping
can also be done using a gradient-echo image, preferably with a flip
angle under 60°, if an accurately
calibrated grey scale or color scale can be supplied with the
image.
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5. How
can I spin a liquid or semi-liquid in a rotor without leaks?
First
some liquids can be very challenging to spin without leaks and there
will be a limit for most methods to the speed that can be achieved
before leaks occur. The Doty MAS sealing cells for XC type spinners
are the best starting point for these types of samples. We have a
variety of sample volumes available and while some volume is always
lost in the use of these cells, they will seal for most liquids and
keep the sample centered in the RF coil. There are also two material
types that will provide a reasonable susceptibility match to most solvents.
Many
aqueous samples where sample volume is not limited and B1 homogeneity
is not an issue can be spun with normal Kel-f or even Aurum turbine
caps up to about 20% of the maximum rated speed for the rotor.
O-ring
caps are another possible option and will provide a larger sample volume. These
caps will usually not stay in very well when used with oily samples.
In
some extreme cases in may be necessary to use normal turbine caps and
glue them into the rotor with super glue. Boiling the rotor in water
afterward will usually cause the glue to release but there is a high
probability of damage to the turbine caps, so this should be a last
resort used with the expectation of throwing away the caps after use.
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6. What
turbine caps do I use for extended VT?
Most
of our turbine caps are not rated for the full VT range of the probe. To
achieve spinning at the extreme limits it is necessary to use an
axial screw turbine cap in most cases. This is a set of turbine
caps with a screw running through the center of the rotor from one
turbine cap to the other. This screw is glued into one of the turbine
caps and put into the rotor. The other cap threads onto the screw
and is pulled tightly into the rotor at the same time. With this
arrangement the caps can not get loose and come out of the rotor
while it is spinning.
Another
extreme possibility is gluing the caps into the rotor with a good high
temperature epoxy. The caps will then have to be drilled out to remove
from the rotor so they would definitely be one-time use.
Please refer to
the MAS Spinner Assembly Materials page
for more details concerning rotor and cap choices.
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