EMC: Electronics system integration for HEP experiments

Transcription

1 EMC: Electronics system integration for HEP experiments (Grounding & Shielding) F. Arteche

2 OUTLINE 1. EMC integration strategy 2. Grounding 3. Block diagram (EMC map) 4. EMC unit analysis Noise emissions Noise immunity Coupling path Cables PCB 5. Conclusions 1 de 54 Meeting on Power Supplies, Services and Grounding

3 1. EMC integration strategy The main goal is to ensure the correct performance of HEP detectors or experiments. Ensure the compatibility in each sub-system Ensure the compatibility between units sub-systems It establishes a safety margin EMC integration strategy is carried out in three stages: Grounding issues (strategy) Block diagram (EMC map) EMC unit analysis Compatibility Compatibility Compatibility SUB1 SUB2 2 de 35 Meeting on Power Supplies, Services and Grounding

4 1. EMC integration strategy It applies TOP-BOTTON-BOTTON-TOP approach Detector-Sub-system-EMC unit EMC unit identification Minimum unit that represents each sub- system EMC unit analysis is carried out by Identification & evaluation of noise sources Identification & evaluation of noise immunity at FEE level Identification & evaluation of coupling paths The identification & evaluation are based on : Standardized measurements Non- standardized measurements Electromagnetic models (simulation) 3 de 35 Meeting on Power Supplies, Services and Grounding

5 2. Grounding What is a ground? It is a reference Uniform reference voltage at any frequency It is a structure to bypass currents Fault (short circuits it..) Noise Reasons for Grounding Safety Equipment protection Equipment performance Golden rule: Make the system safe and then make it work 4 de 35 Meeting on Power Supplies, Services and Grounding

6 2. Grounding Recommendation for good grounding designs: Selection of reference ( grid 3D or plane ) Detector & Experiment level Reinforcement structure Any metal structure t It should have low impedance from DC to High frequency Safety ground & Equipment protection Laboratory codes and European directives. Metal parts that can be energized should be grounded Ground connections - Bonding and straps Ground path should be free of operational currents 5 de 35 Meeting on Power Supplies, Services and Grounding

7 2. Grounding Recommendation for good grounding g designs: Ground to improve the equipment performance Multipoint ground topology is the preferred option Multiple ground connection to ground Digital and analog has to be grounded separate and later connected to common point at board level Electronics, hardware and power parts should be grounded separately at module level and then connected together Ground connection has to be short It has to present low impedance path at high frequency 6 de 35 Meeting on Power Supplies, Services and Grounding

8 2. Grounding One single connection a few cm It resonates 14 MHz Multiple connections It resonates above 50 MHz Main characteristics of multiple ground connections They should be connected to: Opposite corners of the equipment The nearest points on the signal reference grids. Very special cases it can be done via capacitors Several 7 de 35 Meeting on Power Supplies, Services and Grounding

9 2. Grounding Recommendation for good grounding designs: Ground designs to improve the equipment performance At LF Avoid ground loops Detector is a kind of resistor divider where currents flows everywhere At HF Avoid noise currents pass through sensitive parts Everything is connected (real or parasitic impedance) and designing a low impedance paths for these currents All experiment subsystems has to present the same ground topology. They have to be coordinated It is recommended to have an schematic ground design first and later mechanical ground design 8 de 35 Meeting on Power Supplies, Services and Grounding

10 2. Grounding Experiment level 9 de 35 Meeting on Power Supplies, Services and Grounding

11 2. Grounding Courtesy : Dr. Rivetta (SLAC) Plug-in HV Module 12 kv & 200 V power voltages for HPD. Cable length 500 ft Shield Grounding 1G 200 M 10 M 100K 4 CH. FILTER 1M Electrical Backplane Floating low voltage power supplies 1G QIE HV Backplane System level Signal pixel Guard ring 10K 10K QIE Photocathod -High Voltage HPD +Bias Voltage Global & System grounding policy have to be coordinated d 10 de 35 Meeting on Power Supplies, Services and Grounding 80 nf Metal fixture Interface card Equivalent to pixel capacitance V- V+ 0 DPMT card Differential current amplifier

12 3. Block diagram (EMC map) The block diagram is used to : Identify sub-systems Power levels Noise sources and victims Coupling phenomena It helps to define the EMC unit All studies and analysis will be focused on this unit to ensure the correct electronics integration 11 de 35 Meeting on Power Supplies, Services and Grounding

13 3. Block diagram (EMC map) Distribution Bus (AC) Harmonics Radiation Noise AC-DC Transients SMPS Radiation Noise Slow control Conductive Noise Radiation Noise Tracker 25V 2.5V, 125V V Radiation Noise FEE (dc) Radiation Noise AC-DC SMPS Radiation Noise CMS EMC map Block diagram Conductive Noise HCAL 6.5 V, 4.5V 7 kv 12 de 35 Meeting on Power Supplies, Services and Grounding FEE (dc) Slow control Conductive Noise Shielding

14 4. EMC unit analysis HEP experiments are very complex The idea is to define general rules emerging from particular sub-systems systems (TOP-BOTTON-BOTTON-TOP approach) HEP sub-detectors can be considered as isolated system Power Supply & Slow control system only galvanic connection. A reduced model of the sub-system is considered for EMC study of HEP experiment Noise sources PS Victim Coupling path - Cables Victim-FEE P.S. Voltage Distribution FEE Detector Noise source Coupling path Optical Link 13 de 35 Meeting on Power Supplies, Services and Grounding

15 4. EMC unit analysis TEC FEE unit 1 Petal Petal divided in Rings & Modules ICB- Inter Circuit Board HCAL EMC FEE unit 1 RBX Two boards connected PCB 14 de 35 Meeting on Power Supplies, Services and Grounding

16 4.1 EMC unit analysis: Noise emissions Switching converters generates conducted noise At the input & output Two modes of noise emissions (from khz to MHz range) Common mode Differential mode Power switching converter Power switching converter Switching devices Filter Switching devices Filter CM Filter Idm Load Icm Parasitic capacitance of heat sink 15 de 35 DM Gnd Meeting on Power Supplies, Services and Grounding CM Gnd

17 4.1 EMC unit analysis: Noise emissions Common mode (CM) Group of conductors and ground or other conductors Origin in DC/DC converters Magnetic ( di/dt high ) Electric field (dv/dt high) Path - Parasitic capacitive or inductive coupling Differential mode (DM) Conductor pairs (Negative-Positive or Phase-Neutral) Origin direct result of fundamental operation of the device Path Normal electrical l circuit it Abundant energy exchange between modes CM to DM conversion 16 de 35 Meeting on Power Supplies, Services and Grounding

18 4.1 EMC unit analysis: Noise emissions VICOR - HCAL I+ Id Cd Cm + - Icmmeas Icm/2 Icm/2 Output currents (ref. = 50 ohms) 17 de 35 Meeting on Power Supplies, Services and Grounding

19 4.1 EMC unit analysis: Noise emissions 1 unit Vs 50 units Multiple PS units may increase the noise level Design issue - Filtering 18 de 35 Meeting on Power Supplies, Services and Grounding

20 4.2 EMC unit analysis: Noise immunity But..Are the PS noise emission compatible with the FEE?? Do we have enough safety margin? Noise sources that deteriorates the FEE performance are: Intrinsic i thermal noise EM noise picked-up by the connection detector - FEE EM noise picked-up by the connection FEE - Power supply n a (t) = n (t) + n (t) + n (t) th in This noise defines the minimum signal level that the FEE can process Thermal noise dominant effect Design Minimize Thermal noise Characterize the EMI contributions and decrease its effects The characterization of EMI contributions Modeling and simulation of system Robust designs & coupling mechanism Immunity tests on prototypes Weak points & Noise characterization Compatibility 19 de 35 Meeting on Power Supplies, Services and Grounding ps + K

21 4.2 EMC unit analysis: Immunity- Test The main goal is to define the immunity of the FEE to RF disturbances Diagnosis Detection of sensitive areas FEE frequency response to noise Evaluate solutions Noise emission specification from PS Inject a perturbing signal to the FEE and evaluate the FEE performance Frequency range (khz up to 50 MHz or more) Test layout ( EMC unit) as similar as possible to the final configuration Many test configurations may be studied Shield currents CM and DM currents Power lines & slow control lines Test performed on the FEE: EMC unit i ( ) pert t V ( t ) FEE FEE V out 20 de 35 Meeting on Power Supplies, Services and Grounding

22 4.2 EMC unit analysis: Immunity- Test HCAL Reference 8 MHz 20 [RMS Coun nts] Pre-shower Channel number Diagnosis & Sensitive areas HCAL Ground connection photodiodes-board Pre-shower - Ground connections between paths 21 de 35 Meeting on Power Supplies, Services and Grounding

23 4.2 EMC unit analysis: Immunity- Test Frequency enc response It is the noise transfer function (TF) of FEE To quantify the sensibility of the FEE to noise currents Icm External Noise TF Vout (RMS) TF ( ω ) = V I 1out 1cm ( ω ) ( ω ) 22 de 35 Meeting on Power Supplies, Services and Grounding

24 sponse y res ency eque Fre 4.2 EMC unit analysis: Immunity- Test CMS Tracker APV chip PACE chip CMS Presh Tracker FEE Pre-shower FEE 23 de 35 Meeting on Power Supplies, Services and Grounding

25 4.2 EMC unit analysis: Immunity- Test A B Evaluate solutions (HCAL) Ground connection of the shield 3 configurations Length strap & Routing path GND1 - Plot A GND 2 Plot B without cooper sheet GND3 Plot B 24 de 35 Meeting on Power Supplies, Services and Grounding

26 4.2 EMC unit analysis: Immunity- Test 25 de 35 Meeting on Power Supplies, Services and Grounding

27 4.2 EMC unit analysis: Immunity- Test HCAL CM TF - PK APV CM FILTER CM TF - PK APV 632 TF - [ Counts / ma] Frequency y[ [Hz] Tracker Evaluate solutions CM filter performance 26 de 35 Meeting on Power Supplies, Services and Grounding

28 5.2 EMC unit analysis: Immunity- Test Noise emission specification HCAL 3 Topologies (GND, FILTER,NO EXTRA) Very different from standards 27 de 35 Meeting on Power Supplies, Services and Grounding

29 4.3 EMC unit analysis: Coupling path PS units & FEE are connected through power networks Long cables Long PCBs It s very important to study the effect of these power networks in the noise propagation and radiation. It helps to define the EMC environment It helps to established the safety margin among noise emissions & susceptibilities It helps to improve the susceptibility of the FEE (only a very early stage of the design) The analysis can be carried out using: Numerical simulation programs Real measurements 28 de 35 Meeting on Power Supplies, Services and Grounding

30 4.3 EMC unit analysis: Coupling path - Cables Noise propagation effects of long cables in HEP power system The specific configuration of FEE (input capacitors) Attenuates CM & DM voltages I out ( f ) Gain ( f ) = Amplifies CM & DM currents I in ( f ) Cable radiation ICM V V (0)& I, I (0) dm, cm dm cm EMI Filter V dm Cable, V ( L )& I, I ( L ) cm dm cm IDM VDM FEE ICM PS Unit V Gnd 29 de 35 Meeting on Power Supplies, Services and Grounding

31 4.3 EMC unit analysis: Coupling path - Cables Radiation emission from cables may be studied with a simple test Several configurations may be analyzed TSP cable Near field probe (H) BCI probe Current probe PS circuit Load circuit 30 de 35 Meeting on Power Supplies, Services and Grounding

32 4.3 EMC unit analysis: Coupling path - Cables 20 db 30 db The best solution to reduce the effects on the FEE and vicinity of currents flowing through the cable : Connect the shields at BOTH ENDS (at HF) Reduce the ability of cables to radiates One side via capacitor to avoid ground loops at LF 31 de 35 Meeting on Power Supplies, Services and Grounding

33 4.3 EMC unit analysis: Coupling path Cables HF currents flows through h the shield and cable tray Generated by Near and Far fields as well as HF ground currents It couples an small amount of energy in the inner conductors This coupling mechanism is characterized in cables by the surface transfer impedance Its impact is easy to evaluate In case the shield is not present or it is connected only at one end, noise currents are induced directly in the central conductors by external magnetic field Because the low impedance of the circuit associated with those cables 32 de 35 Meeting on Power Supplies, Services and Grounding

34 4.3 EMC unit analysis: Coupling path - PCB Also PCB may radiate and decrease the performance of the FEE As an example CMS Tracker system The main noise source of CMS tracker system is the radiated emission of Power Network (ICB) Radiated noise generated mainly by CM currents injected by Power Supplies Noise currents on power network Magnetic field Not uniform B A C D E 33 de 35 Meeting on Power Supplies, Services and Grounding

35 4.3 EMC unit analysis: Coupling path PCB Bx By dbµv Hx (at 10 MHz) Hx (at 1MHz) 20 A B C D E A B C D E E field Uniform Mod/ Rod E E (at 10 MHz) E (at 1 MHz) 0 A B C D E 34 de 35 Meeting on Power Supplies, Services and Grounding H field Not uniform Mod / Rod

36 5 CONCLUSIONS EMC integration strategy for HEP experiments has been presented They have analyzed the noise sources, coupling path and victim They have presented some design criteria, Grounding policy & EMC requirements & EMC test EMC studies should start at design level It should involves all disciplines Mechanical, electrical All disciplines i has to be coordinated d UNIQUE ENTITY It saves money, time and discussions between groups. CMS upgrade has seriously considered these issues 9.04 : EMC studies for CMS tracker upgrade - Approved EMC requires a systematic analysis to obtain good results It very important to start with simple models (T-B-B-T approach) Extend conclusions for the final system EMC studies requires time & manpower. 35 de 35 Meeting on Power Supplies, Services and Grounding