[Halld-tracking-hw] CDC feedthrus and end plate

[Gerard Visser]

Hi Tim,
	Yes, I know. This (152 direct lines) is what I had in mind. Maybe it is 
too much to ask for. Your question whether we can live without it is a 
good one, wish that I (or Fernando) knew the answer 100% for sure. 
*Perhaps* the answer is yes. If I had to guess, I'd say better than even 
odds.
	One the other hand if you could for instance add the 152 features (4-40 
blind taped hole? or a blind hole to fit a Mill-Max press-fit pin 
socket? or something like this?) to the endplate, then if the eventual 
answer turns out to be no, it does not mean the finished, and I imagine 
rather expensive, endplate is unusable.
	It was the absence of any such features as far as I could understand in 
your drawing, that stimulated this discussion.
	If it is simply impossible to have 152, or even 152/2 or 152/3 or 152/4 
by some sharing scheme, then we must risk doing without it. If it is 
possible, my opinion is the features should be added, they can always be 
left unused if it turns out that we don't need them, i.e., if grounds 
around the outside will not suffice.
	By the way, the boards will (I really hope) be sitting on a ground 
plane, e.g., the upstream plenum is a sheet of thin aluminum, right? 
Because I can pretty much guarantee you that 152 preamp boards with each 
a skinny 40 cm ground wire between the preamp and the endplate, this 
will not work. If the connection is through a common sheet of 
(preferably plated) aluminum, it stands a good chance but I would still 
be nervous that the direct (152 5cm lines) plan might prove to be necessary.
	Well, I think we should consider this more and you'll have to tell what 
you can really do. But the shorter, wider, more distributed the ground 
connections are, the lower the risk and potentially the better the 
performance. We must not forget this :)
	Sincerely,

		Gerard

p.s. Seems this email thread should maybe pop back onto the list to 
involve more discussion, so I did that.

Tim Whitlatch wrote:
> Hi Gerard,
> 
> 5cm (which is really more like 10cm for the longest wires) is not 
> feasible unless you have 152 direct lines (1 for each preamp card) 
> through the gas plenum. Will 40cm long ground wires cause problems?
> 
> Tim
> 
> Gerard Visser wrote:
>> Hi Tim,
>>     I admit, I have not been following all the details... But, I seem 
>> to sense a contradiction here. What do you mean by "direct"? Going 
>> outside the gas volume is indirect (isn't it?). Direct (what I would 
>> like to see) means also ~5cm for the ground connection as you have 
>> achieved for the signal wire connection. Is *that* feasible?
>>
>>     - Gerard
>>
>> Tim Whitlatch wrote:
>>> We can still make direct ground connections to the endplate outside 
>>> of the gas volume.Is it important to be inside the gas volume?
>>>
>>> Tim
>>>
>>> Fernando J. Barbosa wrote:
>>>> Hi Gerard,
>>>>
>>>> Yes, this is a subject that makes me a bit nervous also. I am told 
>>>> this is all we can have due to the area occupied on the endplate, 
>>>> because of gas sealing and straw connections. I would have preferred 
>>>> to have direct connections to the endplate.
>>>>
>>>> Best regards,
>>>> Fernando
> 
>