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Hi,<br>
<br>
Below I discuss issues concerning how to proceed with the quench
detector for the Hall D solenoid.<br>
<br>
Recall the concern is that we currently do not know the coil
inductances in the final configuration, and the Danfysik QD only
works if the sections being compared have a good inductance match.
I am not sure how well they have to match, but Fernando thinks that
10% differences can be handled easily. <br>
<br>
Note that the main problem, as I understand it, is that if you have
to bias the Danfysik a lot so it does not trip during a normal
ramp-up, and you want to maintain good sensitivity, it will likely
trip and cause a fast dump during a normal ramp-down (Fernando or
Mark can elaborate if needed).<br>
<br>
Floyd is quite busy with other things and it probably will be a few
months before he can work on the coil inductances. My worry is that
by the time we find out about the inductances it might be too late
to do something about it before we need to start commissioning the
solenoid.<br>
<br>
After talking with Fernando and Ben I've learned the following
concerning the situation where the Danfysik QD will not work
(Fernando and Ben...please correct me if I misunderstood
something): <br>
<br>
<br>
- For various reasons Fernando does not think we should try to
modify the Danfysik QD to handle large inductance imbalances.<br>
<br>
- If we need to build another QD, Fernando and Ben think the best
strategy is to use a micro-controller based design, rather than an
FPGA-based or an analog design. This is because of the wide variety
of micro-controller boards available, including many with suitable
A/D's build into their front-ends. <br>
<br>
- A new design should easily handle large inductance imbalances.<br>
<br>
- Both believe micro-controllers are robust and reliable from a
safety standpoint as they are used in many safety-related
applications.<br>
<br>
- If we go with a micro-controller, time to
design/procure/build/test is 4 months, EE manpower needed is 1
man-month. <br>
<br>
- More time and manpower would be required if we went with and
FPGA-based or analog design.<br>
<br>
- I don't know whether our safety reviewers will accept a
micro-controller based QD (or even if they'd accept a home-built one
at all!).<br>
<br>
- Fernando is a little dubious about contracting with Danfysik to
have them build us a custom QD matched to our solenoid.<br>
<br>
- I have no idea if there are other companies who build or can
design/build QD's.<br>
<br>
<br>
Finally, from past experience Floyd's simulations have proven to be
accurate at the 10% level or so (Josh...please verify), which means
there is a risk that even if the simulations say the Danfysik QD
will work, in practice it may not.<br>
<br>
<br>
If I take 1-Jun-2012 as the required date for a new QD (leaving time
for commissioning before we begin solenoid testing), then the latest
possible time to know about the inductances is 1-Feb-2012. This
assumes the 4 month estimate is accurate, and that we can get one
man-month of EE time from an experienced designer starting
1-Feb-2012. Building in some float gives 1-Jan-2012, which of
course is just around the corner. If we can wait until 1-Aug to get
the new QD then the simulations need to be completed perhaps as late
as 1-Apr-2012.<br>
<br>
<br>
<u>Options</u><br>
<br>
1. Do nothing yet, hope Floyd completes the simulations in time to
build another QD and that EE manpower is available if and when
needed.<br>
<br>
2. Plan to design and build another QD. In this case we do not
need Floyd to simulate the inductances since we can measure them in
situ and adjust the new QD appropriately. Also, there is plenty of
time to do the work if we get going now.<br>
<br>
3. Do nothing, accept fast dump trips during normal ramp-downs.<br>
<br>
<br>
Comments, criticisms, corrections, alternate strategies...?<br>
<br>
Thanks,<br>
<br>
<pre class="moz-signature" cols="72">--
Sincerely,
Elliott
================================================================================
Those raised in a morally relative or neutral environment will hold
no truths to be self-evident.
Elliott Wolin
Staff Physicist, Jefferson Lab
12000 Jefferson Ave
Suite 8 MS 12A1
Newport News, VA 23606
757-269-7365
================================================================================
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