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Transcript
Overview of the ATLAS Electromagnetic Compatibility Policy 10th Workshop on Electronics for LHC and future Experiments 13 - 17 September 2004, BOSTON, USA G. BLANCHOT CERN, CH-1211 Geneva 23, Switzerland [email protected] ATLAS EMC Policy EMC in TC Quality Insurance TC to insure the application of good EMC practices at design, production, installation and operation levels. Risk Management TC to identify potential risks of malfunctions and degraded performance . Required Performance Reference document is available at: https://edms.cern.ch/file/476490/1/ATLAS-EMC-POLICY.pdf Additional Information is available at: http://atlas.web.cern.ch/Atlas/GROUPS/FRONTEND/EMC/ Addressed issues: 1. Compliance to CERN electrical safety rules. 2. Immunity against conducted and radiated electromagnetic interferences. 3. Control of interferences down to a level compatible with the required performance of ATLAS. LECC 2004 G. Blanchot, CERN 2 EMC Implementation in ATLAS 1 Setup definition: 2 EMC Conformance: Contact person for safety and EMC. How the system must be installed and connected to be operated safely. Fault conditions and protections. Neighbors and the routing of cables. Compatibility Limits. Key parameters: clock frequency, bandwidth, thresholds, intrinsic noise, etc… Conducted noise in cables. CM susceptibility via LVPS cabling. Cable shields requirements. 3 LECC 2004 Commissioning: Cross check compliance to safety rule. Cross check conducted noise levels. G. Blanchot, CERN 3 Grounding Configurations In compliance with the CERN electrical codes TN-S AC Scheme: separation of neutral and PE. Requires ground fault interruptor. L1 L2 L3 N P E L + TN-S DC Scheme: separation of return and PE. Requires over current protection. L P E TN-C DC Scheme: return and PE are common at source. Requires over current protection. L + PEN TN-C DC Scheme: return and PE are common at load. Requires over current protection. L+ PEN L + L - LECC 2004 P E G. Blanchot, CERN IT DC Scheme: floating. Permanent isolation controller (CPI) and over current protection. 4 Electromagnetic Environment Systems Muons Detector Liquid Argon Calorimeter Inner Detector Tile Calorimeter Large dimension shielded systems. Tight gaps between systems over large surfaces. 25 m No interconnect between systems. Presence of magnetic field. Difficult grounding with long cables. Power demanding (4MW) with DC/DC converters. System clock 40 MHz. Toroid Magnet LECC 2004 Solenoid G. Blanchot, CERN 5 Electromagnetic Environment Cabling Very dense cabling into grounded cable trays. High density of trays. Long cables (> 100 m). Trays contain power and data cables, not always possible to separate them. LECC 2004 G. Blanchot, CERN 6 Electromagnetic Compatibility EMI sources Radiated Noise from system is small because at f=40MHz λ=7.5m that is easily shielded by the system faraday cages and enclosures. Radiated Noise from cables comes mainly from CM noise (far field* from electrically short cables). L L ID S Need to control the sources of CM noise in ATLAS: IC S ID d Switched power circuits and converters. IC d Digital circuitry. CM coupling across cables. ED Differential Mode: the far fields are opposed and cancel each other EC Common Mode: the far fields add up. The contribution of CM current to EMI is typically more than 3 orders of magnitude stronger than the contribution of the same DM current. LECC 2004 * Far field region starts at a distance d = λ/6, i.e. 1 m at 40 MHz. G. Blanchot, CERN 7 Electromagnetic Compatibility Near Field in Cable Trays The near field is mainly contributed by the CM noise. Coupling across cables happens inside cable trays in the near field region. The near field dominant component is function of the wave impedance. H field dominates for low impedance loads and decreases at rate 1/d 3. Power circuits, DC/DC converters, 50Ω and 120Ω terminated lines, CANBus. E field dominates for high impedance loads and decreases at rate 1/d3. Unterminated lines, sensors and TTL signals. Non dominant field decreases at rate 1/d2. iStray LM Need to provide separation between cables to reduce their exposure to EMI fields CStray V1 ICM1 V2 ICM2 H fields couple through mutual inductance LECC 2004 Need to shield the cables to contain the EMI fields and to provide some level of protection against it. E fields couple through stray capacitance G. Blanchot, CERN 8 Electromagnetic Compatibility Long Cables The cables in ATLAS are electrically long: L >> λ. They behave as antennas for wavelengths above λ/10 (>300 kHz for 100 m cables) Cables to be modelized as Multiconductor Transmission Lines (MTL). Current and voltage depend of the per unit length parameters. Noise and current get amplified or attenuated at the load for given frequencies. CM turn into DM and vice versa. Power loads usually are unmatched to their power cable. ICM1 RL(N) ICM2 RS(N) ICMn Multiconductor Transmission Line R0 LECC 2004 MTL CM DM I CM 1 I CM 2 I CMn V1 Vcm V1 Vn VCM Vn Need to measure the system sensibility to CM currents in a systematic way. G. Blanchot, CERN 9 Electromagnetic Compatibility Common Mode Return Paths CM currents can return through other cables shields. On large systems, beyond few MHz, the equipotentiallity cannot exist. HVPS Coaxial cable CM currents return to less inductive path: stray capacitances, shields, ground straps. ICM Same tray CStray ICM LVPS Shielded cable ICM VCM ICM Shielded cable VCM ICM dL = 1uH/m dL = 1uH/m CM currents can return through other systems, capacitively coupled, in particular if cables lack of shields to provide the return path. LECC 2004 G. Blanchot, CERN 10 Electromagnetic Compatibility Routing paths Systems must be designed so that: They emit as low CM as possible. They tolerate CM from couplings. Cables must be routed so that: The coupling between systems is minimized. Systems that are sensitive to CM must have their cables away from near magnetic field sources (power): separation of power and data inside a tray. The circuit loop follows the same path. Cables must contain the return conductor: separation of power and data inside a tray. Even DC conductors carry high frequency noise, whose emissions must be minimized. The circuit loops are contained inside a grounded tray. LECC 2004 Preferred with covers. G. Blanchot, CERN 11 Electromagnetic Compatibility Shields Cables are closely packed inside trays: Shield required to minimize emissions. Shield required as a protection against EMI. Shields in ATLAS: effective up to 10 MHz maximum. Aluminium foil. Poor mechanical strength , difficult to connect, high DC resistance: addition of drain wire. Typical transfer impedance = 100 mΩ/m. Good at high frequencies. Copper braid. Mechanically strong, easy to terminate, sometimes combined with Al foil. Typical transfer impedance = 10 mΩ/m. Good at low frequencies. How to connect: One end to ground: Electric field shielding. Both ends to ground: Magnetic and electric field shielding. Allowing cuurent to flow in the shield cancels out the H field inside the affected cable. LECC 2004 G. Blanchot, CERN 12 Electromagnetic Compatibility Compatibility limit CM Noise Current [mA] at a given frequency System S(f) The correlation between CM and system noise must be evaluated. Injected by means of a calibrated injection probe. RF Generator, injection probe, current probe, EMI receiver. LECC 2004 System Noise System dependent parameter. System noise limit sets the input CM noise limit. Note that the system is also a source of CM noise sent outwards. Measured by physics DAQ. G. Blanchot, CERN 13 Measurements: emissions Probe AC Power Link LVPS System Under Test CM Noise DAQ Link 10kHz-100MHz DAQ/DCS Ground plane or on site trays. EMI receiver Att 10 dB dBµV RBW 9 kHz MT 100 ms Marker 1 [T1 ] PREAMP OFF 55.66 dBµV 4.642000000 MHz 1 MHz 100 Example 10 MHz 90 SGL 1 PK CLRWR 70 60 dBμV Voltage computed back to CM current with the current probe calibration curve. Typical values sit in few tens of μA. Peak 80 1 PRN 50 40 30 In lab, a ground plane substitutes the structures and trays that provide the CM return path in ATLAS. 20 10 0 150 kHz Date: LECC 2004 CM noise is contributed by the LVPS and the System under test. Both must configure the ATLAS real setup (no lab devices). 11.AUG.2004 30 MHz 11:25:10 f G. Blanchot, CERN Measurements shall strictly be done with appropriate equipment as described in the policy. 14 Measurements: Immunity Probe AC LVPS Power Link System Under Test DAQ Link DAQ/DCS CM Noise Ground plane Injected current is monitored with the current probe.Typical values up to few tens of mA (up to system failure). RF Generator RF Amplifier EMI receiver Example Normalised System Noise vs CM current 250% Sweep frequency to find worst case peaks. At worst case peaks, modulate amplification up to reach compatibility limit. System Noise increae 200% In lab, a ground plane substitutes the structures and trays that provide the CM return path in ATLAS. 150% 100% 50% 0% 0 1000 2000 3000 4000 5000 6000 7000 1 MHz Injected Common Mode Current [uA] LECC 2004 CM noise affects both LVPS and System: both must be representative of the ATLAS setup and appropriate cabling must be used. G. Blanchot, CERN 8000 9000 Measurements shall strictly be done with appropriate equipment as described in the policy. 15 Conclusion ATLAS EMC Policy: Quality and risk management issue. Establishes methods and procedures to insure the systems electromagnetic compatibility in the experiment environment. Compliance requirements specific to the ATLAS and CERN environments. Procedures: Clear description of the setup: To insuire compliance with safety rules. To define the valid configuration for EMC measurements. EMC Measurements: Specific for each system. Aims to understand how noise couples into a system and affects its performance, within the established compatibility limit. Guidelines: On cgrounding configurations, coupling modes, cable shields, shield terminations routing paths, test methods, tools. LECC 2004 G. Blanchot, CERN 16