Presentation on theme: "M.PEGORARO Grounding Workshop 24th Jan 08 DT GROUNDING & SHIELDING Presented by A. BENVENUTI."— Presentation transcript:
M.PEGORARO Grounding Workshop 24th Jan 08 DT GROUNDING & SHIELDING Presented by A. BENVENUTI
M.PEGORARO Grounding Workshop 24th Jan 08 Analog FE Electronics is inside gas volume of each Superlayer (that is actually a shielding case). Signal connections (data & control) go to minicrate onboard the chamber. Power (5V & 2.5V) for Analog FE arrives to the Splitter Board whose copper heatsink is strongly connected to Superlayers’ enclosures on FE side. The heatsink acts also as common point for the independent returns of supplies. Most of ReadOut & Trigger Electronics are housed in the Minicrate. Power (5V & 3.3V) arrives independently from FE one and the common point for returns is the Al case tightly connected to the Superlayers’s enclosures and to the heatsink of the splitter board. On the other side of Superlayers there are HV boards inside gas volume with GND connection provided by inner Al plates of the layers. 2 HV cables per Superlayer carry voltages and returns; these latter are connected to inner Al plates and decoupled using resistors. Low & High Voltages are obviously filtered at chamber input wrt common GND and with distributed capacitance where loads are applied. All internal connections of the chamber are done through shielded cables except for short ending lengths. Grounding & Shielding Superlayers & Chambers
M.PEGORARO Grounding Workshop 24th Jan 08 shield of HV cable HV ref Sig ref LV ref Input node Inside Superlayer Al Plates
M.PEGORARO Grounding Workshop 24th Jan 08 HONEYCOMB Splitter Board Vcc & Vdd NO RETURN to HV Junction Boxes Splitter Board Heatsink MINI CRATE Inside Chamber Copper Braid to Magnet Iron FE LV Cable Supporting Al frame
M.PEGORARO Grounding Workshop 24th Jan 08 Grounding & Shielding Cables & Braids The enclosures of Superlayers are connected each other and to supporting frame on enclosures with copper braids. Every chamber is a case electrically insulated from magnet iron with supply returns & GND concentrated on the heatsink of the Splitter Board. The Reference Ground (Splitter Board) of the Detector is also Safety Earth; this has no consequence on LVDS signals from Frontend that end inside the Minicrate. A short (600 mm) copper braid connects this point to magnet iron. RPC detector is close, but insulated, to external Superlayers, and is connected to the same point. All cables to/from chamber are shielded with shields connected on detector side. HV and Minicrate LV cables have junctions inside metallic boxes located on iron where cable shields can be decoupled. Connection with DAQ and TRG acquisition on tower racks is done via LVDS AC coupled; DCS communication is done through fibers or floating copper. All of above cables go to Tower Racks at nearest floor (all floors are concerned, with X2 near housing also Acquisition & Trigger crates)
M.PEGORARO Grounding Workshop 24th Jan 08 Grounding & Shielding Tower Racks HV crates in X3 & X4 racks contain floating Voltage Regulators; Voltage Generators are in USC racks and feed (and control) these crates through long cables. So reference and shielding must be shifted from Earth of USC racks at the input to detector GND at the output and we have to take care of common mode noise. Trigger and Acquisition crates in X2 near receive Low Voltage Differential Signals with input compliance of about 1V at high frequencies. Communication with USC is made through fiber optic and they receive power supply from nearby Easy LV crate that feeds also chambers: they are practically insulated. EASY LV system is on X2 and X4 racks and includes AC/DC converters (MAO) and DC/DC converters in cascade: the latters are insulated (with certain limits) from the case while the formers have Safety Earth, and thus chassis, connected to Earth coming from USC S4F zone; moreover their 48V output is also referred to case and so to USC. As a result of not ideal isolation of each DC/DC module from case and rack and direct connection of USC safety Earth to Tower Racks (via MAO’s case) there could be some interference to delicate items like HV and LVDS common mode at the input of acquisition modules; also LV could be affected. We have to consider that Tower Racks contain electronics from several detectors. Also some tests have shown that shielding of cables is of the maximum importance to prevent noise entering that way (the welding machine was an example confirmed by further tests)
M.PEGORARO Grounding Workshop 24th Jan 08 Grounding & Shielding Conclusions (?) We have to prevent as much as possible problems that could arise when the whole detector, including magnet and all power supplies, will be on. One uncertainty is given by Safety Earth that comes from USC S4F to Tower Racks: we ask for some kind of decoupling at high frequencies. The other idea is to have a strong connection from Magnet Iron to Tower Racks at all floors; it should be particularly effective for high frequencies. In this way, connecting to it modules in Tower Racks, we could override the interferences due to the shift of GND reference from USC to detector. The idea is to have a short copper braid with large surface to reduce radio frequency impedance going from magnet iron to a copper panel placed on bottom of each Tower Rack. Also the input reference of DAQ & Trigger modules can use this low impedance connection to iron. Then we could use the strong ground from Magnet Iron to reinforce and test different options for connection of cable shields and Low & High Voltage modules.