[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Preamp tests
Hello everyone,
Yves has a good plan in trying to get the detector working under the
present conditions. I would suggest he concentrates on his step 1 in
trying to remove the oscillations with the new setup.
For a great short summary and guidelines on HV filtering, component
values, etc., I suggest GlueX-doc-753 by Dan Carman. Although this note
was written for the FDC, it applies equally well to the CDC.
I also recently placed a document on the portal (GlueX-doc-927) that
outlines the HV distribution and grounding for the FDC. This also
applies well to the CDC. I will circulate, hopefully before the
holidays, a document outlining the global HV, LV and grounding
distribution philosophy for Hall D - all detectors.
Best regards,
Fernando
Mitch Newcomer wrote:
> Hall D Electronics:
>
> I agree the 33pf cap to shield is pretty small. I'd be inclined to
> hook a 50ohm resistor Shield to the back of the preamp assembly and a
> capacitor on the other end in series with a similar
> resistor. Hopefully this trades off current in the shield with large
> voltage excursions. We also break the copper connection on the HV
> return line using a 1k resistor in series
> with the return to the supply. The filter cap on the HV should be on
> the detector side. The HV supply then has no copper connection to the
> detector HV lines or filtering direct to the supply.
> The potentially noisy HV cable is decoupled at its entrance to the
> detector, not inside the RF shield. -- Mitch
>
>
> Gerard Visser wrote:
>> Hall D Electronics:
>>
>> Hi Yves,
>> I have here 20 capacitors, 330 pF 2.5 kV NP0-type ceramic in an
>> 1808 size surface mount package, Kemet P/N C1808C331JZGACTU. This (or
>> equivalent from AVX or Johanson) is the type I would strongly
>> recommend to use in any new design. It _may_ be possible to use
>> X7R-type ceramic but it is usually not a good idea from a noise point
>> of view.
>> The above capacitors can be ordered from Digi-Key, stock number
>> is 399-4832-1-ND for cut tape packaging. They have stock. The price
>> is rather high if you only buy a small quantity... So my mind was to
>> try them out when I come visit you and then you can buy a large
>> quantity on a reel, suitable for production of some new HV boards.
>> But if you want to try some real soon, order some from DigiKey you
>> can have them in ~2days usually.
>> The coupling capacitor being too small should (I expect) make
>> _absolutely_ no difference to any noise pickup or oscillation
>> problems. So, no need to change the coupling capacitor with a view to
>> fixing that.
>> On the other hand the bypass caps should also be larger, for
>> these I have ordered and received 3.3 nF 3 kV X7R-type ceramic in an
>> 1812 size surface mount package, Johanson P/N 302S43W332KV4E, DigiKey
>> stock number 709-1056-1-ND. Again this is probably what I would
>> recommend to use in any new design. (But a larger value might be
>> dictated by test results.)
>> Surface mount high-voltage ceramic capacitors are much smaller
>> for the same capacitance, primarily because leaded high voltage
>> ceramic capacitors usually use a traditional single-layer
>> construction, whereas the surface mount capacitors are usually
>> multilayer. They are quite reliable and easy to work with when
>> professionally reflow soldered and properly cleaned, but you do have
>> to use extreme care when hand soldering. Certainly they cannot be
>> hand soldered as a production method.
>> About the signal connecting cable, I do believe still that coax
>> is unnecessary _if_ the connections are short. At present your
>> connections are not short. The coax shields should be AC grounded -
>> but of course it needs to be a low impedance ground or else this will
>> just be a source of massive crosstalk. [In particular I think just
>> the 33pF bypass cap on that line is not low enough impedance, but you
>> can try it. The line itself may be too skinny, we'll have to see.
>> Either can be corrected by some hacks to the existing HV board design.]
>> A 2-layer board should probably be just fine for the new HV
>> coupling board design.
>> I suggest as step 1.5 route the input signals directly away from
>> the preamp output cable. This is probably best done my modifications
>> to the way the preamp interposer board connects to your existing HV
>> board. Also improve the ground connection from HV board to the
>> endplate (it should be as short as the signal connections, both
>> running together, and should be as short as possible, and preferably
>> of somewhat low impedance at up to ~10MHz, i.e., use a copper strip,
>> braid, or at least wire gauge 16 or less.)
>> Thanks,
>>
>> Gerard
>>
>> Yves Van Haarlem wrote:
>>> Hi Gerard,
>>>
>>> I asked McCracken how we came to this design: the plan of CMU was to
>>> use
>>> coax cable to bring the signal from the sense wire to the HV board, the
>>> plan was to connect the cable shield to the HV board ground. There
>>> was a
>>> electronics meeting in Indiana where Paul Smith suggested to connect
>>> the
>>> cable shielding to the HV and not to the ground. Gerard opposed the
>>> idea
>>> of using coax cable. The decision on which capacitors to use came
>>> after a
>>> small calculation done at CMU.
>>>
>>> I decided not to connect the cable shielding to ground when bringing
>>> the
>>> HV board outside the CDC end plenum because we saw no difference (using
>>> the old preAMP) with/without connection.
>>>
>>> Plan:
>>> step 1: I just started (together with Mike) to collect the
>>> material to connect the cable shielding to the HV line on the HV board.
>>> After that we will test this.
>>>
>>> step 2: Change the capacitors on the board with the ones Gerard
>>> proposes and test -> Gerard, what type/value do you propose; i remember
>>> you saying we should also using a different type.
>>>
>>> -- My hope is that this can be done in a short period of
>>> time and
>>> that we can take data afterwards --
>>>
>>> step 3: first iteration in redisigning the board (shrink it,
>>> new
>>> orientation preAMp, maybe two ground planes, ...)
>>>
>>>
>>> Cheers,
>>> Yves
>
begin:vcard
fn:Fernando J. Barbosa
n:Barbosa;Fernando J.
org:Jefferson Lab
adr:Suite #10, 12B3;;12000 Jefferson Ave.;Newport News;VA;23606;USA
tel;work:757-269-7433
version:2.1
end:vcard