Re: CDC Interconnect Concepts

[Gerard Visser <gvisser@indiana.edu>]

Hi Yves, Fernando,
	I cc to list, this should be on list I think... The referenced drawings 
could perhaps be posted?
	Anyway, some comments below -->

Yves Van Haarlem wrote:
> Hi Fernando,
> 
> Thanks a lot for your drawings. I agree that a meeting would be very
> useful, Wednesday/Thursday would be best for me. I like the Al shield and
> the grounding rods. I still have to think about the two options but I have
> some questions/comments already, see below:
> 
> 
> On Tue, 10 Jun 2008, Fernando J. Barbosa wrote:
> 
>> In particular, I find the cable length from the straws to the preamp card of
>> about 8" to be excessive and with limited shielding, from outside and between
>> channels. 

Me too. This is an issue not of ease of construction, but of performance 
(EMI sensitivity). Yves, maybe it is in fact impossible to do better, 
but it should at least be recognized as risky and cannot be lightly 
dismissed just because "it only has to be connected once." This is _not_ 
Fernando's main point, I believe.

The task of connecting the cables between the straws and the
>> connectors seems also very difficult.
> True, but in principle it needs to be done only once.
> 
> 
>> Also, the EDAC connectors (series 341) are rated at 1200 VAC rms which is not
>> safe.
> It was proposed by Gerard, maybe he has a comment :-) We also need to test
> how easy it is to make the connector gas tight. I looked for alternative
> connectors (not specified for vacuum because too expensive) but I was not
> very successfull.

Not sure exactly what you mean by "not safe," Fernando. In case we in 
the end use a connector rated at 1200 VAC rms ie. 1700 VDC, it could be 
necessary to get special approval from your safety committee. A high-pot 
test at 200% of our working voltage would probably be passed, and 
considering the very low power level here I would think that is quite 
enough.

But, on the other hand, what part number are you looking at 
specifically, Yves. I just now checked EDAC website, for instance this 
connector looks fairly suitable: 
http://www.edac.net/downloads/306-316-356%20Series%20Spec%20Sheet.pdf
It has a rating of 2545 VDC between adjacent contacts! It comes with 
card guides as an option. Looks good to me.

[Disclaimer: I've not searched exhaustively for all available "old 
style" card edge connectors to find the one I think is best. The above 
is just an example of what should probably work well.]

> 
> 
>> Presently, according to Yves' drawings, the 26 contact connector
>> connects 24 straws and 2 contacts are used for grounding the preamp carrier
>> PCB to some ground point, presumably the end plate.
> Maybe I did it wrong in the drawing but we do not plan to use the two
> remaining contacts for grounding for the reason you mention.

No, Yves, I think you do... Or at least, I think you should. The preamp 
ground to the end plate is as critical, more critical than the anode 
wires connection.

A connector of 26 pins, single row, 0.156" would work well, use the two 
end pins for the ground and use the middle 24 for your signals. Or, 
perhaps better for reliability, if it fits which I imagine will not be a 
big problem, use a 28 pin connector, 24 signals in middle, skip one pin 
on each end (let it float on connector, have no/minimal contact pad on 
pcb, not connected), and one ground pin on each end. This will give some 
extra clearance against surface leakage or breakdown on the pcb board.

> 
>> The HV to a group of 24
>> straws  may still be operational even if a wire breaks in a straw and this
>> may create a condition where there is a 3 kV difference between adjacent
>> cables and adjacent contacts on the EDAC connector.
> I agree, but how do you get to 3~kV, I can only think of <2~kV?

I'm also a bit confused on your point, Fernando - the straw bias 
resistors are not being sized to withstand 3kV constinuously... So, this 
must not be an issue, or there are wider implications.

	- Gerard

> 
> 
> Cheers,
>         Yves