Hi All,
Kirk is correct. These connectors are a PITA and it is worse if you have
a dual solids/liquids instrument.
I share the concern about introducing a jumper inline. It will introduce
errors in temperature. At a minimum one should recalibrate the VT system.
There is a source for these pins. We purchased a slug of both genders
for both the Cu and the constantan leads. However, in our experience it
is the Cu one that fails repeatably. Omega sells these
(
http://www.omega.com/pptst/SM_SUB-D_CONN.html). Part # SMTC-CU-S for
the female and SMTC-CU-P for the male, replace "CU" with "CO" for the
constantan.
While having a source of spares is nice the repair is a much bigger
pain, especially for those like me with big, klutzy fingers. Ideally one
would like these not to fail in the first place. To this end I have,
over the years, adapted our setup to minimize this.
Take off the stupid clips on the D-shell connector that "secure" the
cable to the probe. I have found that this is a source of unnecessary
flexing. Then incorporate either Sara's or Wei Li's suggestion to secure
the cable to something nearby to minimize the droop on the connection.
After spending an obscene amount on a new cable I decided to put a
splint on the connector. This is the land of disposable chop sticks so
mine are made of wood and are about 15 cm long. I would suspect that the
handles off of a plastic knife would work just as well. I start at the
connector and use electrical tape to wrap it securely to the connector
and run it up the cable. This will *NOT* flex. I have not had issues since.
I guess one could make a right-angle adapter so that the cable hangs
straight down. our Nalorac probe has the 9-pin D-shell on the bottom of
the probe which accomplishes this. The old Varian probes are difficult
to modify.
Walt
On 3/21/13 9:49 AM, Kirk Marat wrote:
> Continuing the Varian/Agilent VT cable thread...
>
> Like many others, we have had our share of difficulties with these cables. Since our INOVA system runs both solids and liquids, our VT cable is actually for the Chemmagnetics VT upper stack, and we need an adapter cable to go between the 15 pin Chemmagnetics cable and the 9 pin connector on the Varian liquids probes. This effectively doubles the number of connections that can fail. Since the cable has to be moved back and forth between the two positions, the "lash it to the magnet leg" option is not really workable. Anyone who has replaced these cables will know that they are not cheap.
>
> The reason that these cables fail, I think, is that the normal pins in the connectors have been replaced with pins made out of thermocouple material: copper and constantan. These pins are more prone to oxidation than the regular gold-plated pins, and are not as mechanically robust as regular pins. A few flexes back and forth will distort the pins so that they no longer make reliable contact. Anyone who has looked at the thermocouple connections on, say, an Omega digital thermometer or even on the back of the Oxford VT (or a Bruker BVT) unit will see that they are very large and fit very tightly in the socket. A potential problem with using a regular serial cable as an extension (to reduce flexing at the pins) is that you now have junctions of dissimilar metals, which may introduce stray thermocouple potentials that will have an effect on temperature accuracy and stability. This is likely the reason that they changed the pins in the first place.
>
> Has anyone found a reliable permanent fix to this problem? I guess periodically replacing the pins might be an option if there is a source for them. Has anyone retrofitted a different thermocouple connector to a Varian probe? I am thinking of a LEMO or Omega type connector.
>
> Cheers!
> Kirk
>
> Kirk Marat, Ph. D. NMR Facility Manager
> Dept. of Chemistry, University of Manitoba
> Winnipeg, Manitoba (Where this winter is never going to end! -25C yesterday! last year: +22 C!)
> R3T 2N2, Canada
>
> Ph: (204) 474-6259 FAX: (204) 474-7608
>
>
>> -----Original Message-----
>> From: Li, Wei [mailto:wli_at_uthsc.edu]
>> Sent: March 20, 2013 1:55 PM
>> To: kunz_at_brandeis.edu; Stolowich,Neal J.
>> Cc: ammrl_at_ammrl.org
>> Subject: RE: AMMRL: VT controller has no gas flow
>>
>> I thought this might be another solution to consider for people who encountered this
>> problem: Similar to Sara and others, I had the exact same problem with our Inova-500 a few
>> years ago. I just bought a serial cable used for computer devices and made the connection
>> between the probe and the original VT cable. I then fixed the end portion of the original VT
>> cable and its connection to the serial cable to the magnet leg using a few cable ties to
>> prevent any movement or stain to the VT cable. The computer serial cable is very flexible,
>> and as far as I know, we never had VT problems since then. I initially worried about possible
>> issues with shielding in using the computer serial cable under the magnet, but the spectra
>> seem to be perfectly fine, so I guess that is not a problem.
>>
>> Best regards,
>>
>> Wei Li
>> --------------------------------
>> Wei Li, Ph.D.
>> Associate Professor/Faculty Director of Instrument Facility
>> University of Tennessee Health Science Center
>> 847 Monroe Avenue, room 327
>> Memphis, TN 38163
>> 901-448-7532 (PH)
>> http://www.uthsc.edu/pharmacy/pharmsci/faculty/wli/
>> Email: wli_at_uthsc.edu
>>
>>
>> -----Original Message-----
>> From: Sara D Kunz [mailto:kunz_at_brandeis.edu]
>> Sent: Tuesday, March 19, 2013 1:44 PM
>> To: Stolowich,Neal J.
>> Cc: ammrl_at_ammrl.org
>> Subject: Re: AMMRL: VT controller has no gas flow
>>
>>
>> Several years ago, after a lot of frustration with Varian VT cables, I decided to support the
>> VT cable so that it would not hang down putting stress on the connector and to keep it out
>> harm's way. I wrapped a bungee cord around one of the magnet legs and arranged the VT
>> cable under the cord on the inside of the magnet leg and then connected it to the probe.
>> There was no longer any stress on the connector and the cable is was out of the way. I no
>> longer get calls that are related to the VT controller.
>>
>> Sara Kunz
>> Brandeis
>>
>> On 3/18/2013 2:16 PM, Stolowich,Neal J. wrote:
>>> I have noticed this a couple of times on my VNMRS 700 as well. A few
>>> cycles of resetting the VT and pneumatics, perhaps with rebooting the
>>> console in between does fix it, but I'm curious as well if there is a
>>> specific fix, rather than randomly resetting things.
>>>
>>> Regards,
>>>
>>> Neal
>>>
>>> Neal J Stolowich, PhD
>>>
>>> NMR Facilities Manager
>>>
>>> Department of Chemistry
>>>
>>> University of Louisville
>>>
>>> *From:*Xuemei Huang [mailto:xhuang_at_ucsd.edu]
>>> *Sent:* Friday, March 15, 2013 7:26 PM
>>> *To:* ammrl_at_ammrl.org
>>> *Subject:* AMMRL: VT controller has no gas flow
>>>
>>>
>>> Hi, Everyone,
>>>
>>> We have a 800MHz Varian VNMRS spectrometer equipped with cold probe.
>>> Recently I am running into a problem where I can not regulate the
>>> temperature. After I set the temperature, I see the VT starts
>>> flashing, indicating it's trying to change the temperature. But the
>>> temperature never changes. I tried to reset the VT controller, the
>>> pneumatics, as well as resetting the console. None of them seemed to
>>> solve the problem. The error message I am getting is that : VT
>>> controller has no gas flow. But I checked that there is sufficient air
>>> flow. Has anyone seen similar problem on this system? Any suggestions
>>> would really be appreciated.
>>>
>>> Thanks,
>>>
>>> Xuemei
>>>
>>> ***************************************************
>>>
>>> Xuemei Huang
>>> Department of Chemistry and Biochemistry University of California, San
>>> Diego
>>> 9500 Gilman Dr.
>>> La Jolla, CA 92093
>>> xhuang_at_ucsd.edu <mailto:xhuang_at_ucsd.edu>
>>> (858)-822-2307
>>> ***************************************************
>>>
>>>
>>>
>>>
>
--
Walter P. Niemczura
NMR/Mass Spec. Facility Director
Department of Chemistry
2545 McCarthy Mall
University of Hawaii
Honolulu, HI 96822
Ph: 808-956-3113
FAX: 808-956-5908
Email: walt_at_hawaii.edu
Received on Fri Mar 22 2013 - 08:59:52 MST