Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 1 Design, Manufacture, Transport and Integration on-site in Chile of ALMA Antennas EMC ANALYSIS PM#03 Torino - April 5th- 6th, 2006

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 2 EMC Self-compatibility ALMA ANTENNA ARCHITECTURE ACU communicates with ABM and El. & Az. Motors by CAN BUS CAN BUS Characteristics The CAN bus is a balanced (differential) 2-wire interface running over either a Twisted Shielded Pair (TSP), Twisted Pair (TP), or Ribbon cable; Impedance: 124Ohm termination (between + and – terminals) ACU CAN Bus El. & Az Motors Encoders 1kHz CAN Bus ABM

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 3 EMC Self-compatibility IEC Standard ( Radiated Radio-Frequency Electromagnetic Field Immunity Test ) The EMC Standard defines the radiated immunity test for ALMA electric / electronic equipments. The incident Electric Field Level is of 10V/m on the Equipment Under Test (EUT). EMC Model (COMMON MODE) INPUTS A ribbon wire on ground plane AWG24 cable, length 10m Parametric analysis: h=1cm and 5cm (W.C.) An incident electromagnetic wave with the electric field of amplitude 20 V/m Zs=10 Ohm//50nF Zload=124 Ohm + common mode impedance

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 4 EMC Self-compatibility EMC Model (COMMON MODE) Results A maximum of 1.4V is expected from our analysis as differential voltage on Zload impedance. The ISO 11898−2 specification (CAN spec.) lists a common mode voltage specification of −2.0 V (on CAN_L) to +7.0 V (on CAN_H) for the data lines. Conclusion The estimated coupled voltage is of the same order of magnitude of common mode noise that the CAN BUS can manage. It is better to reduce the coupled voltage using TP or TSP cable.

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 5 EMC Self-compatibility CABIN RECIVE SHIELDING – ALMA REQUIREMENTS The measured shielding effectiveness shall be 20dB at 12GHz. Proposal Design The shielding of the receiver cabin is achieved through: -Walls (aluminum on CFRP); -Roof (aluminum on CFRP); -Floor (steel on CFRP); -Cabin door (aluminum on CFRP); The inner walls of the receiver cabin shall be an effective continuous metal surface for RFI shielding and RFI shielding continuity shall be provided on the door. Considerations Electric field coupling is often insignificant when well-shielded enclosures are used. Magnetic field coupling is more serious problem: it can penetrate by diffusion, apertures and conductive penetrations.

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 6 EMC Self-compatibility Current Diffusion Definition of “skin depth -  ”: it is the point where these fields are reduced by a factor of 1/e (~ 0.37) In table is reported the SE considering a metallic barrier with thickness T= 10μm and an infinite surface. Material  - 1MHzSE–1MHz T.=10μm SE-12GHz T.=10μm Copper66μm1.3dB150dB Aluminum85μm1dB112.6dB Steel430μm0.2dB59.8dB Carbon3mm0.03dB3.2dB Conductive Penetrations (only for information) Wires and Tubing have not to enter inside the enclosure in order to avoid Antenna effects, as for picture on the right. The shield has to be connected on the external face of the case.

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 7 EMC Self-compatibility SUMMARY The CAN BUS (but it could be generalized of each lines) has to use TP if is important to prevent coupling with magnetic field but it is better to use a TSP if a shielded barrier must be crossed. Each wire, which has to cross a shield, has to present an overall shield if a consistent shielding effectiveness is required. A pig-tail connection must be avoid. The shield has to connected to the ground on both sides of the terminations. Shields have not to be used intentionally as return lines for power and signal with exception of the RF coax lines.

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 8 EMC - LEMP Analysis Reference Standard:IEC The IEC Standard considers two stroke: first and subsequent stroke. For both currents the following parameter are provided: Parametersfirst strokesubsequent stroke I200kA50kA h 11 19μ0.454μ 22 485μ143μ The subsequent stroke is the quickest but the first stroke have a more important energy. EMC MODEL – BIOT-SAVART LAW The Biot-Savart law permits to calculate the magnetic field produced by a steady state current at a distant s (0.5m in our analysis) from the straight wire. A shielding effectiveness of 40dB was considered for Receiver Cabin.

Reproduction interdite © ALMA EUROPEAN CONSORTIUM Reproduction forbidden Design, Manufacture, Transport and Integration in Chile of ALMA Antennas Page 9 EMC - LEMP Analysis Conclusion: In figure is reported the estimated magnetic field at 50cm from the straight wire, produced by a lightning event (with a shield effectiveness of 40dB) it is mandatory that each electric/electronic supplier provides an accurate analysis/assessment/test which confirms that no problems are encountered when the equipment is subjected to the magnetic field reported in figure.