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Re: CDC Connectors
Hi Yves,
I will provide a drawing and I think I added to much detail in my email,
but I don't think it is that complicated. However, labor is always a big
part of any cabling.
Earlier, I considered a PCB to attach the cables to and soldered to the
connector, I think that's what you are referring to. The problem is that
the cables are then perpendicular to the connector/PCB plane and need to
be bent 90 degrees towards the straws. I think the space between
connectors is very limited.
The copper plate with 24 holes that I mentioned is a way of connecting
all the braids to the HV and is similar in function to the second PCB
with the advantage that the cables are oriented properly. The labor is
still the same for both - soldering the cables with braids.
Most importantly, this installation technique, with either a copper
plate or PCB, allows us to have a minimum space between the straws and
the electronics, perhaps 1-2 inches, instead of 8 inches.
As for ground connections, the shorter the better. After primary
ionization, electrons drift towards the anode and + ions drift towards
the straw. The anode is connected to the preamp and the circuit is
closed through the ground connection to the straw. So, we must provide a
low impedance (direct) connection from the preamp ground to the straw
for the return current. Relying on the Al-plate attachment is not good
enough because of the higher impedance. The Al-plate must be connected
to ground and the endplate of course, but the signal return current to
the straw must be made with a thick, short wire from each of the
connectors to the endplate in the vicinity of the straw. Because there
are 24 straws connected to the HVB card, this ground connection must be
made to a location enclosing these 24 straws. Another consideration is
that we need a thick wire jumper(s) to actually make the connection from
the endplate to the Al-plate because electrical connections through
screws and bolts are not reliable enough. I will include this into the
drawing.
Thanks for your comments. Regards,
Fernando
Yves Van Haarlem wrote:
> Hi Fernando,
>
> Thank you very much for all the info. I forwarded your mail to Gary
> Wilkin.
>
> I believe I can more or less picture it and things on the connector
> side look pretty complicated to me. I was wondering if we could not
> make a second pcb (a very simple one) where we solder all the (24)
> signal cables, grounding, shield braids to on one side. This pcb is
> being fed through the end cover and on the other side it has the
> connector soldered to it which could be sealed. Also Gary had some
> ideas but he is not in this week.
>
> Couldn't we connect the HVB ground to the end-plate via the Al-plate?
>
>
> Cheers,
> Yves
>
> /--------------------------------
> / Yves Van Haarlem
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>
> On Sat, 2 Aug 2008, Fernando J. Barbosa wrote:
>
>> Hello everyone,
>>
>> I have attached a pdf describing the edge card connector from EDAC.
>> This is similar to the one Gerard suggested but in 0.156" contact
>> spacing. The connector part number is 307-030-500-202, which is a 30
>> contacts on dual row with a HV rating of 1800 V AC rms,
>> Thermoplastic Polyester insulator and $3.05. I searched for similar
>> connectors and Sullins also has a similar one rated at 1800 V DC but
>> with a different insulator (PPS Ryton). However, the cost for the
>> Sullins part is five times higher at ~$15. The EDAC connector is
>> stocked at Newark.
>>
>> Now for the assembly details which are based on Slava's drawings.
>> Slava, I would appreciate if you could email your drawings to those
>> on this distribution list.
>>
>> The assembly attempts to minimize the cable length from the straw to
>> the connector:
>>
>> 1. 24 RG-174 cables are prepared as follows:
>> a. Strip both ends so that there is the center conductor for
>> soldering, insulation of center conductor, braid and outer
>> insulation. Each is about .125 long so there are steps (different
>> diameters).
>> b. On the straw side, prepare as is now planned with solder ball and
>> conductive rubber. Maybe a heat shrink piece could be applied to
>> secure the conductive rubber cylinder and cover the shield in one step.
>> c. On the connector side, slide each of the 24 cables into a small
>> copper plate (perhaps a bit less than .125 thick) with 24 holes and
>> solder the shield braids at the exit of the holes. The shields will
>> all be connected together to the shield HV and to 2 connector pins.
>> Solder each of the 24 center conductors to the connector.
>>
>> 2. The connector has 24 pins connected as in 1.c above, the next 2
>> adjacent pins connect to the copper plate to the shield HV, as in 1.c
>> above. The next two pins are left unconnected and insulated or cut.
>> the final 2 pins are soldered to a cable to attach to the endplate
>> for grounding (ground on card is connected to endplate in this way.
>>
>> 3. The back side (soldered connections) is sealed with the proper
>> viscosity sealer and with low out-gassing characteristics (no
>> silicone here). The finished part forms the connector assembly.
>>
>> 4. Connect all the cables from all the cable assemblies to the straws
>> and endplate (grounds).
>>
>> 5. Attach dummy boards with straps to the edge card connectors on
>> each of the cable assemblies.
>>
>> 6. Position the gas plenum Plexiglass cover and feed all the straps
>> through their respective holes on the Plexiglass cover. Slide this
>> cover while pulling or straightening the straps until the cover
>> touches the connectors. Attach the connectors with screws, washer and
>> neoprene seal washer.
>>
>> 7. Rotate CDC so that connector side is at top.
>>
>> 8. Apply sealer (see 3 above) around each of the
>> connectors/plexiglass holes.
>>
>> In this way, we only need a short distance between the straws and the
>> gas plenum cover. This is not very elaborate but I can provide a
>> drawing if necessary to better explain this technique. Please note
>> that if one of the wires in the straws brakes and shorts tripping the
>> HV, all the 24 channels in the group will be off. This is required
>> because the shields are also at HV and the RG-174 is not rated for
>> this level of HV. So, this is inherently safe.
>>
>> There will also be an aluminum plate or aluminized mylar cover over
>> the whole gas plenum and grounded for shielding.
>>
>> Please provide feedback so we can finish the design of the HVB PCB.
>> The HVB PCB will have the HV distribution network, the connections to
>> the preamp card connector, grounding, etc. The preamp card, as in the
>> FDC, is removable from the HVB.
>>
>> Regards,
>> Fernando
>>
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