LIGO-G040XXX-00-D

EMC Upgrade Progress Overview

M. Zucker

30 July 2004

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Recap of 11/22/02 EMC Review

Approved/funded: Phase I (power, grounding, digital containment)o Replace switching power supplies w/linears (L1, H1, H2)o Segregate digital (+ telcom, video) from analog by rack (L1, H1, H2)o Reform DC power, signal and safety grounding* (L1 Ex, L1 Ey)o Shielded VME crates, EMI filters, cabling (L1 Ex, L1 Ey)o Shielded EMC racks, cabling, feedthroughs (L1 Ex, L1 Ey)o Shielded/alternative/new wave cross-connects* (L1 Ex, L1 Ey)o Ancillary resolutions (all implemented)

– Improved analog protocols for new designs (HEPI, FSS, ISS, RFPD, etc.) – EMC planning and testing integrated in design & prototype process– EMC testing part of commissioning at observatories

o Incorporate lessons learned while propagating to H1, H2 Evaluate results before designing Phase II (analog

shielding/repackaging, sensor & driver isolation) LATER ADDITION: Move to separate room for acoustic isolation

*Substantial design evolution since 11/02

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Cross-connect Interim Solution

Replicate existing open terminal block setup inside separate EMI-sealed enclosure with filtered I/O

Pro: o Pin-compatible upgrade path, minimum

downtime to convert existing system o VERY FAST switchover!o Retains rework flexibility, no new

infrastructure required

Con: o Doubling of cables and connectors

(reliability, loading)o Minimal improvement in intra-rack

crosstalk immunity (TBD)

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Grounding system

Recall our dilemma: o RF shielding demands contiguous grounding, no gapso 60 Hz & audio ground loops require ground isolation, “star” grounding; but inductance

makes ground useless for RFo Isolation transformers help but introduce safety grounding issueo MZ proposed frequency-dependent “hybrid grounding”

2003 electrical code permits balanced powero 60 Hz power for instrumentation supplied through balanced transformer; ground is

defined at center tap of secondary (connected to technical earth grid)o No induced currents in ground => no “ground” potentialso Now used widely in audio studios

Pro: o Signal and shield grounds can generally be connected without interference, forming

good RF shield coverage without ground loops (but breaking loops is now safe too) o Extreme isolation from power grid noise, facilities, vacuum equipment, etc.

Con:o MUST power ALL loads, test instruments etc. from balanced power; random wall plug

not just a ground loop any more, but DAMAGE

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Balanced power transformer/breaker; tech power drop

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HEPI @ corner sta., feedthru panel @ Ey

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Rack I/O filter panel

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Shielded/enclosed VME crates & feedthrough back panels

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Parting shots

Work is about 6 months behind schedule; limited by both available manpower & opportunities (commissioning gaps)

Switchover speed has been optimized to limit downtimeo Offline building and wiring as much as possibleo Moving to a separate space decouples build from ongoing commissioning

Some issues/concerns still in work:o Circuit loading by RFI feedthrough capacitanceso Connector reliabilityo Opto-isolated Ethernet links

Evaluation still in progress (some prelim. results to show) Corner station move scheduled week of LSC, shakedown

expected to take the rest of August