[Halld-controls] Options for Hall D solenoid quench detector

[Elliott Wolin]

Hi,

Below I discuss issues concerning how to proceed with the quench 
detector for the Hall D solenoid.

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.

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).

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.

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):


- For various reasons Fernando does not think we should try to modify 
the Danfysik QD to handle large inductance imbalances.

- 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.

- A new design should easily handle large inductance imbalances.

- Both believe micro-controllers are robust and reliable from a safety 
standpoint as they are used in many safety-related applications.

- If we go with a micro-controller, time to design/procure/build/test is 
4 months, EE manpower needed is 1 man-month.

- More time and manpower would be required if we went with and 
FPGA-based or analog design.

- 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!).

- Fernando is a little dubious about contracting with Danfysik to have 
them build us a custom QD matched to our solenoid.

- I have no idea if there are other companies who build or can 
design/build QD's.


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.


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.


_Options_

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.

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.

3.  Do nothing, accept fast dump trips during normal ramp-downs.


Comments, criticisms, corrections, alternate strategies...?

Thanks,

-- 

				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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