Hi All,
Many thanks for your replies - I've got them here for you. Some
centre on ingenious ways to relieve the stress and strain on the connector,
and a few have replaced the connector themselves.
No-one likes the setup, and this seems to be another example where
Varian stubbornly refuses to make a common problem go away. One colleague
noted that the faulty connector can cause the probe temperature to increase
out of control, and that should be reason enough to re-engineer the device.
If you DIY then checking against the VT standard may be a good idea.
See:
http://www.spectroscopynow.com/Spy/tools/temperature.html
Many thanks,
Mike
PS I asked the Varian UK Service Dept for an engineering comment but had no
response.
PPS My apologies for restarting a thread.
=================================================================
I have replaced the shells and connectors on Varian VT connectors
with no problems. Two of the wires are the thermocouple connections with
copper-constantan connectors but replacing them with standard copper
connectors simply adds comparable junctions on both sides. I used crimp
connectors to avoid solder junctions. As long as you check the sample
temperature with an external thermocouple there should be no error.
=================================================================
For a few dollars (pounds) you can get the parts for the serial
connection, and in about 30 min. you can re-solder the connector and
make it more robust than the ones Varian sells. I've done a couple here
and been very pleased.
=================================================================
We have the same problems, both with console communications and VT cables.
The VT cable problem crops up occasionally due to a flaky cable. After
futzing with it for a while and then taping it stationary, I can usually get
it going again for a few more weeks. Because the connector is standard, the
end can be replaced rather than the entire cable. After replacing the cable
once, I then had a spare to repair and be ready for the next time.
==================================================================
I feel your pain. We have also had a few issues that turned out to be a VT
connector at the probe that went wonky. I think that it is the dumbest way
to connect the cable that I could come up with. Perhaps we should send them
an old Bruker probe to study. Best of luck with your quest, I for one would
like to see it changed for something that is a bit more sturdy.
==================================================================
There was a thread on this not long ago in AMMRL, with an agreement that the
design of the VT connector is terrible, and a strong recommendation from the
folks involved to Varian that they change it (it all started with one user
wondering why Varian didn't change the design with the new probe body
design).
Of course, none of that helps you with your current problems (other than to
know that you are not alone). I suggest you put something in place that
will remove most of the strain from the cable weight when it's connected to
the probe, if you haven't already done this. We use a simple cable tie loop
to feed the cable through that take most of the weight off the connector.
That helps a lot.
==================================================================
I had been under the impression that problems also arose from pinching and
bending the thermocouple cable. Our solution has been to make little
stainless hooks that we've then bolted to the bottoms of the magnet cans,
aligned radially with the standard position of the VT jack on the probe (to
the extent that this is possible given the few bolt holes in the bottom of
the can and the constraint on probe orientation from the VT gas line or what
have you). The VT cable then rests on this hook and goes straight to the
probe: no bending at the connector.
==================================================================
You can slightly distort the male pins in the DB-9 connector by squeezing
them (away from the field) with a pair of needlenose pliers. Be gentle.
You can also save the rubber bands off your brocolli or celery and use them
to keep the cable snugly attached to the probe - this will help eliminate
the gradual opening up of the individual pin sockets as the weight of the
cable stresses the connector. I know, I know, such a high-tech solution.
If you are in a real pinch, carefully insert small pieces of aluminum foil
into the pin sockets to fill the void with a conductive material. This
will make any true engineer shake his or her head in disgust.
But the above solutions may help get you back up and running until your new
cable comes in.
==================================================================
I was having a similar problem, although not as serious as you describe. I
average around three probe changes a week, do solids, a lot of high and low
VT and not all the liquids probes have the connectors on the same side of
the probe. VT errors were common. Fortunately, in our case the solution was
a lot easier than I'd expected. It wasn't that our cable or connector had
suffered any permanent damage from our "mistreatment" of it, but there was
quite a lot of play in the connection from the frequent reconnections and
the weight of the assembly was readily facilitating partial disconnection,
particularly if contractors slammed external doors or users bumped the cable
when tuning and so on. But at least for us the solution has been simple, as
I said. Given no actual damage to the cable, I found that if I simply drew
out more cable (ours had been very neatly restrained when the new console
was commissioned - which was otherwise great I hasten to add - our
engineer's excellent to work with) and looped it out and around/above our VT
support arm (a large Al cross bar attached near the top of the magnet legs -
which you may or may not have on your system) and then brought it back down
to the connection/s our problems went away. Attached in this manner the
cable is no longer in the elbow space used for tuning so it never gets
brushed against and, more importantly, gravity and cable tension work for us
as I can ensure the cable is pushing into the connector ensuring consistent
snugness of fit for the duration.
If your cable end currently occupies more "near floor" space than "near
magnet" space you may want to try a new feed strategy.
==================================================================
We also make frequent probe changes on our spectrometers so there is
a lot of wear and tear.
We have modified the cables on all of our Inova-class spectrometers
because of continuing problems with VT, some dangerous (read-back
wrong and the heater goes ballistic...that's happened twice and
damaged one probe, fried $5K worth of protein).
Our solution is not perfect and so perhaps the user group will have a
better plan: my electronics guru replaces the entire cable assembly,
including pins, solder, etc. and reinforces it (with a 90 degree bend
to accommodate the way some of our probes fit around other stuff in
the way). This has made a HUGE difference. Not one of these
modified cables has failed. EVERY Varian cable has failed in one way
or another.
One idea that I had originally but did not follow through on was to
make a short leader that would attach to each probe "permanently".
Then the console-VT cable would attach to the leader in a more rugged
way.
==================================================================
Personally, I find it amazing that Varian has taken so long to do something
about this VT connector. They do seem to deteriorate, and the process of
detaching ours can vary from infuriating to equipment-endangering.
My understanding is that Varian is aware of the issue, but hasn't chosen to
take action on it yet, either bacause they don't realize what a problem it
is, or because they haven't figured out what to do about backward
compatibility. But I don't have any official word from anyone there.
==================================================================
You can save money by ordering the connector kit. Varian doesn't like to
sell them but they do have them in stock and they use them to repair
returned cables that go into service part stock. If you didn't know already
service stock is separate from those parts found in new consoles and is all
basically reconditioned so for future reference on new installs that need
parts make sure they aren't from service stock.
You can use a normal db9 connector set for everything but the thermocouple
matching pins (copper and constantan.) Whether it is for the probe or for
the cable these are the frailties of the setup.
If you are handy there are tools that may be purchased from electronics
suppliers to remove the pins from any DB connector. If the copper and
constantan pins are serviceable they can be replaced into a new connector.
I think it uses normal electronics grade solder.
Something you can try, if you have soldering expertise is to hit all of the
connectors on solder side with a tiny amount of flux and heat each
connection until it is pooled and shiny. A good little vise and well tinned
solder iron is the key.
As far as general comments on the connections to Varian probes. Pathetic!
We pay $10K-50K for some of these probes. The parts that connect to the
instrument are subject to constant use and cost less than $50 for VT,
signals and PFG total. I would like to see gold plated BNC for the signals
and sealed cannon plugs for VT, spin and PFG all with gold connectors
(except TC). It would perhaps add $200 more per system.
Received on Mon Nov 29 2004 - 09:56:46 MST