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AIDA GELINA BRIKEN nToF CRIB ISOLDE CIRCE nTOFCapture DESPEC DTAS EDI_PSA 179Ta CARME StellarModelling DCF K40

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Entry time:	Sat Mar 29 11:26:16 2025
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> > During investigations into the noise today by NH and OH a couple of findings were made on the grounding of the FEEs and Adaptor boards. > > > > - The adaptor boards have no connection to the FEE ground over the ERNI connector > > - Currently we are providing one via a ground cable between the FEE Al cooling and the Lemo ground on the adaptor board > > - The Al cooling plate is not electrically isolated from the copper plate on the ASIC and both are connected to the electrical ground on the FEE > > - Verified with 0 resistance between plate and HDMI ground shield > > - The FEE is electrically isolated from the frame but when cabling is connected they show 0 resistance > > - With electrics disconnected but water still connected they show 200kOhm > > - With the bias core going to FEE14 and the braid going to FEE8 better performance in FEE14 is obtained by disconnecting FEE8 adaptor board from the ground > > - The cost of this is the rate of FEE8 goes up to 300k > > - It is essential to have the adaptor board ground on the FEE ground but unsure why having both adaptor boards connected to their respective grounds makes one worse > > - The resistance between all FEEs is not zero. Some show a 5Ohm and some show a 35Ohm resistance between each other > > > > The adapter boards have ERNI ground pins, and the FEE64 has a grounded plane on its ERNI connector, unfortunately the orientation means the ground pins do not touch the plane on the FEE64 and hence no contact is made > Would require installing board "upside down" but then the ASIC connections would be wrong. A new adapter board layout would be necessary to correct this > > Tomorrow will investigate direct connection of all FEE64s to mechanical ground via dedicated copper cable. > Currently FEE64s get ground via Pulser(->NIM) ((weak ground)), HDMI(->NIM) ((possibly?)) and Power(->PSU) (primary grounding) > HV Bias is floating at NIM side and so does not provide ground path (intentional) > TD may have ideas to isolate pulser from AIDA FEE ground > Unsure if HDMI ground is a problem > > The ground quality via the power may not be ideal over long cables of relatively thin wire. (5 * 20 AWG) and then unsure how ground of PSU connects to mechanical ground > Explicit grounding may help keep resistance between FEEs < 1 Ohm. > > Will also mount a DSSD and see situation without pulser, with/without mechanical grounding and maybe with various LK jumpers. Encoding: HTML ELCode plain Suppress Email notification

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