ATLAS EMC Technical Note

ATLAS EMC Policy
EDMS NUMBER: ATC-TE-IP-0001 Date:
04 August 2004
EDMS ID:
476490 Georges Blanchot
VERSION:
2 Georges.Blanchot@cern.ch

Abstract
Electromagnetic compatibility of ATLAS electronic equipments must be insured toachieve the expected level of performance of the experiment. The ATLAS EMC Policy covers
the electrical safety aspects of the front end and racked installations, and aims the proper
operation of the experiment in the electromagnetic environment that it creates. For this, thepolicy defines a set of procedures to document and approve the installations from the safety,
compatibility and maintenance points of view.

Contents
1.

INTRODUCTION ................................................................................................ 4
1.1. SCOPE OF THE POLICY. ........................................................................................ 4
1.2. INTERNATIONAL STANDARDS. ............................................................................. 4
1.3. POLICY IMPLEMENTATION. .................................................................................. 4
1.3.1. System Installation Report.......................................................................... 5
1.3.2. Electromagnetic Compatibility Report....................................................... 5
1.3.3. Commissioning Report. .............................................................................. 6
1.3.4. Measurements and Support at CERN......................................................... 7
1.4. ATLAS POLICY ON GROUNDING AND POWER DISTRIBUTION. ............................ 7

2.

ELECTRICAL SAFETY..................................................................................... 8
2.1. VOLTAGE DOMAINS. ........................................................................................... 8
2.2. EQUIPMENT. ........................................................................................................ 8
2.3. INSTALLATIONS................................................................................................... 8
2.3.1. Power Distribution. .................................................................................... 9
2.3.2. Cable trays. .............................................................................................. 11
2.3.3. Services..................................................................................................... 11
2.3.4. Supports.................................................................................................... 11
2.3.5. Earth connections in UX15. ..................................................................... 122.4. INSTALLATION VERIFICATION............................................................................ 122.5. SAFETY PROCEDURES. ....................................................................................... 123.

ELECTROMAGNETIC COMPATIBILITY.................................................. 13
3.1. ELECTROMAGNETIC ENVIRONMENT................................................................... 13
3.2. USE OF RADIO EMITTERS. .................................................................................. 15
3.3. COMPATIBILITY LIMITS. .................................................................................... 15
3.4. BASIC MEASUREMENT INSTRUMENTATION. ....................................................... 16
3.5. USE OF GROUND PLANES. .................................................................................. 16
3.6. LINE IMPEDANCE STABILIZATION NETWORKS. ................................................... 16
3.7. SHIELDING AND INSTALLATION OF CABLES....................................................... 17
3.7.1. Shields. ..................................................................................................... 17
3.7.2. Installation of cables. ............................................................................... 18
3.8. EMISSIONS TESTS AND MITIGATION. .................................................................. 19
3.9. IMMUNITY TESTS. .............................................................................................. 20
3.10.
ELECTROMAGNETIC SURVEY. ........................................................................ 21

4.

REFERENCES ................................................................................................... 225.

ANNEX 2. ABOUT INTERNATIONAL STANDARDS................................ 25

Index of Tables
TABLE 1: SYSTEM INSTALLATION REPORT .............................................................................. 5
TABLE 2: ELECTROMAGNETIC COMPATIBILITY REPORT........................................................ 6
TABLE 3: COMMISSIONING REPORT ......................................................................................... 6
TABLE 4: COMPATIBILITY LIMITS .......................................................................................... 15
TABLE 5: INSTRUMENTATION FOR CONDUCTED AND RADIATED NOISE TESTS. ..................... 16
2

Index of Figures
FIGURE 1: AC TN-S CONFIGURATION. ........................................................................................ 9
FIGURE 2: DC TN-S CONFIGURATION......................................................................................... 9
FIGURE 3: DC TN-C CONFIGURATION. ..................................................................................... 10
FIGURE 4: VARIANT OF THE DC TN-C CONFIGURATION ............................................................ 10
FIGURE 5: DC IT CONFIGURATION............................................................................................ 10

History of Changes
Version Date
DRAFT.3
1

14 June 04
21 July 04

Page
7
9-10

11

22
2

04 August 04

18

Description of Changes
First draft. Submitted at EB in July 04.
Edited section 1.4.
Edited section 2.3.1. on power distribution
schemes to accommodate grounding close to thedetectors, in agreement with SC rules.
Added sections 2.3.1.5 and 2.3.1.6 about sense
wires and common grounds.
Edited section 2.3.2 about cable trays.
Added reference number 21.
Added section 3.7.2 about installation of cables
and power/data separation.

3

1.

Introduction

1.1.

Scope of the Policy.
To achieve the expected level of performance of the ATLAS experiment, theelectromagnetic compatibility (EMC) of the electronic installations must be insured. Three
topics must be covered:Compliance to electrical safety rules applicable at CERN.
Immunity against conducted and radiated emissions present in the experimental area.
Measurement of conducted and radiated emissions of each installation in theexperimental area.

The compliance to electrical safety rules is mandatory at CERN and is insured by the
Safety Commission. The characterisation of emissions and immunity of each system isnecessary in order to identify EMC hot areas or incompatibilities between neighbouring
equipments. The main reference documents of this policy are the ATLAS Policy on
Grounding and Power Distrubution [1], the IEC 61000-5-2 technical report on EMC [2], the
LHC Technical Note “Liaisons equipotentielles et protections electromagnetiques” [3] and theFrench Low Voltage Code NF C 15-100 [4]. The information relevant to this policy can befound at the ATLAS EMC site:
http://atlas.web.cern.ch/Atlas/GROUPS/FRONTEND/EMC/

1.2.

International standards.
Pieces of equipment acquired from industrial vendors shall comply with theinternational standards for industrial environment, in particular EN 61000-6-2 and EN 610006-4. The level of immunity required (immunity criterion) shall be established on a case bycase basis. Compliance to international standards isn’t required for custom made equipment,
however their EMC performance must be evaluated.

1.3.

Policy implementation.
The EMC policy is implemented as a set of three procedures that target the approvaland proper documentation of the installations from a safety, compatibility and maintenancepoints of view. The systems targetted by this policy are described in Annex 1. The documents
associated with it are stored in EDMS and are available at the ATLAS EMC web site.
SystemInstallation
ReportElectromagnetic
Compatibility
Report4

Commissioning
Report1.3.1. System Installation Report.
The systems and associated front-end and racked electronics which form an
installation must comply with mandatory electrical safety regulations of CERN. This first
document, whose content is detailed in Table 1 is required for:

Approval of the installation by the Safety Commission
Documentation of the installation.

System Installation Report.










Identification of contact person for safety and EMC procedures.
Description of equipments, parts and components that compose the installation.
Identification of commercial CE marked equipment and report of theirconformance to international standards.
Identification of non CE marked and custom made equipment to be approved by
the Safety Commission.
Description of how the equipments must be installed and interconnected to be
operated safely, including grounding aspects.
Description of the fault conditions and protection systems.
Description of the cables routing paths and identification of the next neighbours on
this path.
Definition of a checklist that allows to crosscheck that the installation is done
properly.
Definition of a procedure to clear electrical faults.

Approval of this document by the ATLAS EMC coordinator and by the Safety Commission
is mandatory.

Table 1: System Installation Report
1.3.2. Electromagnetic Compatibility Report.
The equipments, components and parts that form a system installation as described in
the System Installation Document, do not require to comply to any specific international EMC
standard because of the particular EMC environment of the experiment. However, their EMC
behaviour must be known. Therefore, measurements shall be carried out and an EMC Report
is still necessary:To understand and define the limits of good operation of the system.
To identify the levels of emissions of the system.
To draft afterwards a map of emissions in the cavern that will allow to set theelectromagnetic compatibility level of the system at its location.

5Electromagnetic Compatibility Report.






Definition of working and non working limits of the system and the parameters toevaluate the margin to these limits.
Identification of key parameters such as operating frequencies, bandwidths,
transmission methods, thresholds, power supplies topologies, cables lengths andproperties, electronic noise.
Measurement of conducted emissions in cables and ground straps.
Measurement of CM susceptibility through power supply cables.
Definition of a check procedure that allows to cross check at installation theperformance of the system according to the EMC Report.

Approval of this document by the ATLAS EMC coordinator is mandatory.

Table 2: Electromagnetic Compatibility Report.
The type and quality of cables shields shall be explicitely defined. The ways shields are
terminated shall be defined, together with the type of backshells, connectors and frontpanels
selected. Grounding of shields at one or both sides of the cable shall be explained.
The type and quality of enclosures that are used for the electronic boards shall bedefined. Enclosures are susceptible to resonate at given frequencies. When possible, thosemodal frequencies shall be defined.

1.3.3. Commissioning Report.
Once installed in the experimental area, a final crosscheck must be carried out :To insure the compliance of the system to its System installation Document.
To insure the compliance of the system to its EMC Report.

The crosschecks should be made according to the check procedures established in the
installation document and in the EMC Report.

Commissioning Report.
Electrical safety crosscheck report.
EMC compliance report.
Measurement of final performance of the system: working limits parameters andmargin to non working limit.

Approval of this document by the ATLAS EMC coordinator is mandatory.

Table 3: Commissioning Report61.3.4. Measurements and Support at CERN.
The following measurements are mandatory and will be carried out with the support of
the CERN Safety Commission and/or the ATLAS EMC responsible:

Grounding scheme conformity for each installed equipment and system.
Emissions and immunity of installed front end electronics and their associatedpower supplies.

Assesment on good EMC practices at board design level and system integration isavailable through the ATLAS EMC coordinator.
Technical support, in form of standard equipment and expertise to carry out specificmeasurements is available through the ATLAS EMC coordinator.

1.4.

ATLAS Policy on Grounding and Power Distribution.
The preliminary guidelines for grounding and power distribution in ATLAS are defined by the
ATLAS Policy on grounding and power distribution [1]. The systems shall be designed inorder to be electrically isolated between them and from ground.At installation time, thedetectors are to be grounded to the safety network of the cavern in a controlled manner andaccording to the power distribution schemes defined in section 2.3 of this document.

7

2.

Electrical Safety.
The applicable standard at CERN is the CERN Electrical Code C1 [5], which refers to
the french national code, known as NFC 15-100 [4].

2.1.

Voltage Domains.
The voltage domains for installations as defined by the IEC are described in the Safety
Instruction 33 [6].
Equipment and installations in ATLAS are not provided with double or reinforced
insulation, and therefore they must be grounded to a protective earth conductor. In general,
equipment and installations shall be implemented in a way that provides protection against
direct and indirect contacts when the involved voltages are above 50VAC(rms) or 120VDC :



2.2.

Protection against direct contact with live conductors. This is achieved withinsulated active parts or enclosures.
Protection against indirect contacts, that is contacts with conductive parts
that might become active under fault condition. The protection is in form ofground fault interruptor and/or overcurrent interruptor.

Equipment.
Electrical and electronic equipment that provide a direct function which is CE marked
shows conformance to the applicable EU Directives, including the Low Voltage Directive
89/336/EEC on which is based the french code. Components and equipment with no directfunction do not require to be CE marked.
Electrical and electronic equipment that provide a direct function which isn’t CEmarked or is custom made may be authorised to operate on CERN premises by the Safety
Commission. The assessment is on low voltage electrical safety, fire risk and nuisance to theimmediate neighbours. A documentation folder must be submitted to the Safety Commission
for approval, containing:






2.3.

Schematics including power and earth paths;
Cable lengths and sections;
Possibilities of direct contact;
Protections (fuses or others);
Capability of power sources involved;

Installations.
The ATLAS electrical and electronic installations are combinations of front end
detectors with their supports, services (pipes for gases and fluids), cables and cable trays,
racks and crates with electrical, electronic, computing and communication equipment. These
installations must be built with pieces of equipment which are either CE marked or approvedby the Safety Commission. The overall setup must comply with the CERN Electrical Safety
Code C1.

8

2.3.1. Power Distribution.
2.3.1.1. AC TN-S configuration
The AC network that distributes the power to the ATLAS experiment is in TN-S
configuration (Figure 1): the neutral is earthed at the secondary star point of the maintransformer, the earth conductor is routed separately from the neutral conductor, and the casesof the equipments are connected to the earth (PE) conductor. A ground fault differential
interruptor is to be placed at the power input of each installation and will open the circuit withthe first ground fault. The fault current rating has to be specified according to the load.
L1
L2
L3
N
PE

Figure 1: AC TN-S configuration.
The power distribution of the ATLAS front end systems is done in DC. It must be noted thatground fault differential interruptors are not required on DC networks, and protection isinsured with overcurrent protection devices or fuses. The power supplies that deliver the DC
power from the AC power network are located in racks off-detector and are either regulated or
switched-mode power supplies. Specific international standards apply to these units (seeannex 2). The DC distribution network can be implemented in TN-S, TN-C or IT
configurations:2.3.1.2. DC TN-S configuration.
In a DC TN-S configuration, a protective earth conductor PE is routed parallel to thepower return line. The PE conductor is earthed at the rack and connects to the front end cases.
A fault between L+ and PE or L- will cause a short circuit condition. The protection can be
implemented as trip down feature of the power supply or an overcurrent protection device(fuse or equivalent).

L+
LPE

Figure 2: DC TN-S Configuration.

92.3.1.3. DC TN-C configuration.
In a DC TN-C configuration, the power return is earthed at the rack level and connects to thefront end cases; here, the case is the return conductor of the front end equipment. The power
return is the protective earth conductor (PEN). A fault will cause a short circuit condition. The
protection can be implemented as trip down feature of the power supply or an overcurrent
protection device (fuse or equivalent).
L+
PEN

Figure 3: DC TN-C Configuration.
A variant of the TN-C configuration, with the grounding connection made close to the load
rather than close to the source, is accepted (Figure 4). If a ground fault between the power
return and the ground appears at the source, an alternative short circuit return path throughground is provided, but difficutly detected. In this configuration, the ground connection (wirecross section, connectors and mechanical links) must be able to sustain the short circuit
currrent if a ground fault appears at the load too.
L+
PEN

Figure 4: variant of the DC TN-C configuration

2.3.1.4. DC IT configuration.
In a DC IT configuration, the outputs are left floating. However, the front end case has
to be earthed. The first ground fault condition will not create a hazard by itself (a leak current
will be created through stray capacitances only), however provisions must be made to prevent
hazards in case of a second ground fault. The protection must be implemented in form of
permanent isolation controler (CPI) that will monitor the impedance between L+- and earth at
the source, together with a safety procedure to clear the fault. The first ground fault must be
detected and an alarm must be raised in the DCS system so that the fault can be identified andcleared. The second ground fault can cause a short circuit condition: for this, overcurrent
protections are required in form of fuse or trip down.

L+
L-

PE

Figure 5: DC IT Configuration.
10

2.3.1.5. Sense wires.
In agreement with Safety Instruction IS48 [21], the sense wires used to regulate at thesource the voltage delivered at a remote load must be provided with current limiting devices
such as resistors or fuses, in order to limit the eventual fault currents. The current limiting
devices shall be installed on both wires, as close as possible to the sense connections at theload.
2.3.1.6. Common returns.
Power supplies providing mulltiple outputs with a single common return line are notallowed, unless provisions are made so that the cabling is capable to handle the full shortcircuit current.
The derivation of a power supply output from an equipment such as a crate to power aremote load is not allowed, as a short circuit condition might create a fire hazard in the
remote load and its cable. In these cases, auxiliary power supplies shall always be used.
2.3.2. Cable trays.
All cable trays are earthed with a PE conductor bonded inside the tray and must be
installed in agreement with Safety Instruction IS48 [21]. Multiple levels of trays are bonded
together at regular intervals. The racks supplying the cables to the tray must be earthed to thattray . Meshed trays by themselves cannot be used as PE conductors.
In order to reduce the electromagnetic emissions of cables, they shall be laid as close
as possible to the tray surface [3]. Cables shall be grouped in terms of power and sensitivity to
disturbances, and appropriate separation between those groups shall be provided [3]. Power
cables shall be routed on the tray surface and as close as possible to the PE conductor.
From the EMC point of view, cable trays act as a ground plane for the system.
2.3.3. Services.
Pipes for gases and fluids are to be earthed for safety purposes. However, they cannot
be used as protective earth PE conductors.
2.3.4. Supports.
The structural conductive parts are to be earthed to the nearest ground connection forsafety reasons. However, they cannot be used as protective earth PE conductors. The front end
systems installed on these structures must be earthed by means of an adequate PE conductor.
Grounding all conductive parts will provide a meshed ground structure that will
improve the EMC proformance of the front end systems [2,3]. Cables shall be laid on
grounded structures and trays to reduce emissions.
Aluminium structures that are bolted shall be connected to the safety ground meshwith a dedicated copper wire. Electrical continuity across bolted aluminium parts shall bechecked at installation for EMI control purposes.

112.3.5. Earth connections in UX15.
Earth connections are provided exclusively by means of 120 mm2 copper wires,directly bonded to the electrical distribution PE conductor. All safety ground connections
require a specific ground wire. For EMI control purposes, passive structural elements shall bebonded to the grounding network, but cannot be used as safety ground connection point.
The steelwork and beams of the UX15 experimental area building are grounded atsurface. A meshed ground network is welded to the cavern steelwork. This network is
grounded to the USA15 grounding network through the TE galleries, and is directly bonded
to the secondary star point of the transformer. The HO and HS structures are grounded as wellto the cavern grounding network.
The HO and HS structures located inside UX15 are made of painted beams that areeither soldered or bolted together. Because of this, the ground continuity cannot be insured as
is. The main beams of those structures are bonded to the safety ground mesh. The other beamsof the structure will be indirectly grounded through the bolts; when the quality of theconnection is iinsufficient, ground starps shall be added.

2.4.

Installation verification.
The installation must be done in a way that it allows to cross check its safety
grounding. The verification method must be documented in the System Installation
Document.
Specific and independent measurements to insure the proper grounding of metallic
structures and installations will be carried out by the Safety Commission. Additional
measurements shall be requested to the ATLAS EMC responsible.

2.5.

Safety procedures.
To clear the ground faults in any of the configurations described above, a proceduremust be documented in the System Installation Document. This is particularly important in the
IT configuration.

12

3.

Electromagnetic Compatibility.

3.1.

Electromagnetic environment.
As an underground facility, the ATLAS experimental area is up to some extent
shielded against electromagnetic fields that are usually present at surface: broadcast radio, TV
signals, and satellite radio signals. The fields present underground will be contributed mostly
by the CERN radio services and by the experiment itself. Some radio signals are however
broadcasted inside the cavern:

Voice radio bands (151MHz, 155MHz, 161-169MHz, 174MHz, 451-462MHz).
Radiocontrol for the UX15 cranes, occupying the 433MHz and 869MHz bands.
GSM radio (886-942 MHz) is broadcasted by two antennas. .
Wireless LAN occupying the 2.4-2.484 GHz band.

The EMC Policy aims to insure the proper operation of the experiment in theelectromagnetic environment that it creates. Because of this specific statement, thecompliance with international EMC standards that are applicable for industrial andcommercial equipment do not represent a guarantee of proper operation for the experiment,
and might set too stringent or to loosy constrains on the front end electronics. However, insake of consistency, the parameters for immunity and emissions measurements have to be
defined for the ATLAS environment, and the measurement methods must be specified. A
front end system must be implemented so that it is immune to the fields created by its
neighbours; on the other hand, each front end system must limit its emissions at a level that iscompatible with the operation of its direct neighbours. The reference to international standards
is useful to settle down the measurements methods, but a full compliance for undergroundequipment is not mandatory in ATLAS.
On the other hand, equipment located at the surface will be exposed to the full
spectrum of electromagnetic fields, and therefore the compliance to the EMC international
standards for the equipment installed at this level is strongly encouraged. The basic EMC
standard applicable in ATLAS is the IEC-61000 standard. The measurement techniques andinstrumentation is contained in the IEC harmonized standard CISPR 16; for information
technology equipment, the measurement techniques and instrumentation is contained in theharmonized standard CISPR 22.
The electromagnetic disturbances are conducted through cables and are radiated to theenvironment in form of electrical and magnetic fields. The nature of those disturbances
depend of the involved coupling paths and frequencies. Several groups are identified that willcontribute to most of the electromagnetic environment in the ATLAS experimental area:

13












Switched mode power supplies, with switching frequencies from few kHz up to
few MHz. Taking into account the frequency content of the transient switching
waveforms, the SMPS will contribute to noise up to few MHz. At thesefrequencies, conducted noise will dominate.
Fieldbus links, with baud rates up to 1 Msps and taking into account harmonics
of digital waveforms, will contribute to conducted noise in the range of few
kHz up to few MHz.
LHC clock driven systems, will contribute to conducted and radiated noise infrequency ranges from few hundreds of kHz (for systems running at lower
frequencies derived from the main 40MHz clock) up to few hundreds of MHz
for harmonics of digital waveforms running at the main 40MHz clock. As
those systems use mainly optical links for the transmission of information,
radiated noise from the front end systems and from the readout crates will
dominate.
RF frequency of the LHC machine (400 MHz) might show up in theexperimental area.
Gigabit links: the data links drive the optical signals in the Gbps range. The
SerDes chips of these links operate in the GHz range and are susceptible toradiate locally high frequency noise.
Magnetic field fluctuations at startup and shutdown of magnets, speciallyduring quenching.
50 Hz and harmonics of AC power rectification circuits, for instance ofmagnets power supplies (LHC magnets, toroid magnets, solenoid).
Particle showers are themselves noise sources in the RF spectrum [12].

LHC clock driven systems

Gbit drivers

Fieldbus

kHz

Conducted

1 GHz

500 MHz

40 MHz10 MHzPower

Radiated

GHz

Because the analog front end electronics bandwidth is limited to a maximum of 40
MHz, it can be seen that the conducted noise from power and fieldbus systems will be themost critical one because it is susceptible to impact directly on the resolution of physics data.
LHC clock driven systems and Gigabit links drivers, usually located in crates or in front end
faraday cages, will radiated locally and can be at the origin of unexpected error rates orintermittent failures. The LHC clock driven systems will be at the origin of coherent noise
all over the experiment. A gap in the range of hundreds of MHz will exist due to the lack ofsystems operating in this range of frequencies.
14

The conducted noise dominates and will take the form of common mode noise, that iscurrent flowing in the same direction toward a system, with the return path being the ground(conductor or surrounding conductive elements). This common mode current can be at theorigin of electromagnetic fields if the circuit loop is large, and contribute in this way to theradiated EM environment of the experimental area.
To control the electromagnetic environment of the experiment, the Policy focuses on
two major work lines:



3.2.

Measurement and mitigation of conducted emissions of systems and equipment.
Survey of radiated emissions in the experimental area.

Use of radio emitters.
The usage of radio controlled equipment is regulated at CERN. The installation of radiotransmitters in the experimental area must be autorized by the ATLAS EMC responsible andby the IT division, who maintain a database of emitters to avoid interferences between
systems.

3.3.

Compatibility limits.
A system is considered to be working in its environment if it is able to resolve thesmallest signal with the minimally required resolution. A loss of resolution is interpreted as adegradation in the RMS value of the measurement, or as the inability to digitze and/ortransmit the result through the data links. A system is disturbed through cables (conductedsusceptibility) and through interferences (radiated suscpetibility). The compatibility limits
must be defined for a complete system, that is with its power supply and DAQ system
connected, under power and taking data. The evaluation of the RMS values of pedestals anderror rates of data links are usually sufficient to set the compatibility limit condition. Other
specific parameters can be defined for each system if needed.

Compatibility limits parameters: analog circuitryAnalogue variable to monitor:
Intrinsic noise:
Compatibility limit:

X
∆X
∆XMAX

Compatibility limits parameters: data links
Intrinsic error rate:
Compatibility limit error rate:εεMAX

Compatibility limits parameters: specific parameters

Other specific parameters and limits may be defined if needed.

Table 4: Compatibility Limits

15

3.4.

Basic measurement instrumentation.
The EMC measurement must be carried out with appropriate instrumentation as
described in Table 5. The ATLAS EMC Policy is mainly focused onto the dominantconducted emissions in the range comprised between 10kHz and 500MHz.
Instrumentation for conducted and radiated noise tests











EMI receiver 9kHz-1.5GHz minimum, or:Spectrum analyzer with quasi peak detector and appropriate IF input filters.
Current probes for conducted emissions measurement , up to 100MHz minimum.
Injection current probe for immunity test, up to 100MHz minimum.
RF Generator and amplifier, for immunity test.
Line Impedance Stabilization Network (LISN) for AC powerline emissions.
Loop antenna for magnetic field emissions, up to 30MHz.
Monopole antenna for electric field emissions, up to 30MHz.
Dipole antenna for electric field emission, above 30Mz and up to 1GHz.
Ground plane.

Table 5: Instrumentation for conducted and radiated noise tests.

3.5.

Use of ground planes.
Cables in ATLAS are routed in grounded cable trays that act as a ground plane for the
installation. The use of grounded cable trays is of great importance for EMI control because it
provides the return path for common mode currents in a contained loop. Therefore, emissions
measurements in lab or at testbeams shall always be done with cables either laying on a
grounded copper plane when trays are not used, or alternatiivelly with cables routed ingrounded trays or structures. In all cases, and in particular for measurements done at testbeam
areas, the equivalent ground plane shall be provided.
For large installations such as testbeams or the ATLAS experimental area where aground plane cannot be inserted, the cabling shall be done in grounded cable trays or along
grounded strautures. Structures and cable trays shall be interconnected. In this configuration,
the CM currents follow a controlled least inductive path.

3.6.

Line impedance stabilization networks.
Measurements of conducted emissions on power lines done in laboratories require theusage of line impedance stabilization networks (LISN) to normalize the measurements.
However, measurements done in situ (i.e. at testbeam areas or in the experimental area), do
not require the usage of LISN as the setup is the final one.

16

3.7.

Shielding and Installation of Cables.

3.7.1. Shields.
Because of the cabling density of the experiment, all copper links (power and signal) areclosely packed together inside grounded cable trays. The length of the links can be rather
long. All cables are to be considered as potential electromagnetic radiators and at the sametime as antennas. As radiators, the near field will depend on the cable topology andtransported energy. As antennas, the induced voltage will be a function of the near field and of
the cable topology. To minimize the coupling between closely packed cables, shields shall be
used. There are several types of shields, of coupling mechanisms and of ways to connect theshields: this subject is extensively covered in the litterature [13]. The performance of a shieldis evaluated by its transfer impedance. In ATLAS, shielded cables shall always be used.
The most commonly used shields are the aluminium foil and the tin plated copper
braid. The shielding effectiveness is a function of the frequency but also of the way the shieldis connected at its ends. Aluminium foils are usually laminated on polyesther foils to improvetheir mechanical strength. The aluminium layer is usually very thin, and this results in a low
mechanical strength and high DC resistance. The resulting transfer impedance is usually about
100 mΩ/m. This type of shield is however close to the ideal tubular shield, which is of interest
at high frequencies. In order to improve the DC resistance, a drain wire is usually supplied.
Because of its fragility, when bended and stretched during installation, some gaps can becreated in the foil, and affect the resulting shielding effectiveness.
The braided shield is mechanically much stronger, and it offers better transfer
impedance, around 10mΩ/m. The shielding effectiveness is limited at high frequencies by theshield topology. Typically, the transfer impedance start to degrade at around 1MHz. The
cutoff frequency is a function of the optical coverage, which shall not be less than 85%. To
improve the performance at higher frequencies, aluminium foils can be wrapped inside thebraid, and a drain wire issually added.
The shield is an electromagnetic barrier. When grounded on one side, it forms anequipotential that protects the circuits against electric field couplings. Because the current
cannot flow, it does not provide any protection against magnetic field couplings. In order toprovide some degree of protection against near magnetic fields, both ends of the shield shallbe grounded, allowing current to flow [13]. In all cases, a shield will only behave properly if
no impedance is added in series to ground; at most, a capacitive connection to ground can be
tolerated at expense of DC shielding effectiveness. Resistive connections shall be avoided,
because they will develop voltages in the shield and impeach the energy to flow to ground,and therefore it will flow through sensitive circuits.
The shielding effectiveness is vastly affected by the way it is grounded at its ends.
Metallic backshells, with 360 degree contact around the shield shall be used with theconnectors. It is demonstrated that pigtails limit the shielding effectiveness to few kHz.

17

3.7.2. Installation of cables.
In addition to the rules defined in section 2 about cables trays, services, supports andearth connections, the routing of cables shall be made in order to minimize couplings acrossthem. The rules that apply to the installation of cables are detailed in the IEC 61000-5-2
technical report on EMC [2]. The coupling between cables is proportional to the coupling path
length they share, to the current they carry (magnetic field surrounding the cable), to thevoltage they carry (electric field coupling), to the transients speeds, and is inversely
proportional to the separation between them. The shields are effective against electric field
couplings if properly grounded; they are however of limited effect against magnetic field
couplings, which is particularly important in power circuits. The most effective technique tominimize magnetic couplings between cables is the distance. The guidelines are summarized
as follows:
•

•

•

•

The cables must be grouped (and bundled) in terms of their sensitivity to interferences andcontribution to noise:o Very sensitive: sensors, front end and trigger signals.
o Sensitive: slow control signals, low speed serial and parallel links, for voltages
below 24VDC.
o Noisy: 220VAC lines, relay and switch lines without protection.
o Very noisy: lines that feed AC and DC motors, switched power supplies,
frequency variators for AC motors.
Separate the different groups and bundles of cables:o Noisy bundles and sensitive bundles should be routed in separated, grounded
metallic trays, and when possible on different paths.
o When noisy and sensitive cables share the same tray, the distance between them inthe tray must be maximized.
o When power and noise sensitive cables have to share a common tray overdistances greater than 15 meters without separation between them, both cables
shall be shielded and grounded at both ends.
Minimize the circuit’s loop area:o The coupling is proportionnal to the area exposed to magnetic fields, therefore thereturn lines shall follow the same path as the live lines of a given circuit.
o The insertion of switches and interlocks in a control line must be done so that it
does no increase significantly the loop area of the circuit.
Minimize the length of antennas:o Circuits provided with switches at the source and normally opened form antennas
that feed the detector with picked up interferences. Therefore, those circuits shallbe provided with common mode filters at the interface to the detector.
o When possible, the switches should be located close to the detector to reduce theantenna length when disconnnected.

In practice, power equipment should be grouped in a given area, and the asssociatedcables are bundled together and routed on power trays, far away from sensitive equipment,
which is usually installed in a separated area, with the associated sensitive cables bundled
together and routed on signal trays. Both trays and sets of cables will come together close to
the detector (less than 15m). In this way, the coupling length is minimized and the volume of
the trays is efficiently used.

18

3.8.

Emissions tests and mitigation.
Conducted emissions tests carried in laboratories shall be done on appropriate groundplanes, or at least with grounded cables trays or with cables laid on grounded structures, withcalibrated current probes and with an EMI receiver or spectrum analyzer equipped withquasipeak detector.
Data Links
Probe
AC

Power Link

LVPS

CM Noise

SystemUnder
Test

DAQ/DCS

Ground plane

Analyzer

Analyzer

The conducted emission measurement shall be done for spectrums comprised between
10kHz and 100MHz. The main peaks frequencies shall be recorded together with theiramplitude. The spectrum diagram shall be reported in the EMC Report.
Emission on AC powerline done in laboratories shall be carried out with anappropriate LISN to normalize the AC plug impedance and allow for repeatible measurements
independently of the plug used.
Emissions of commercial power supplies must comply with the standards and thesystems powered by those units must be capable to withstand the level of noise created bythem. Emissions of custom SMPS must comply with the compatibility level of the system it isintended to power.
Data Links
AC

LISN

LVPSPower Link

SystemCM Noise
Ground plane

Analyzer

19

DAQ/DCSWhenever possible, the systems should implement mitigation techniques to reduce asmuch as possible their conducted emissions. This is achieved with:







3.9.

Cables carried into grounded cable trays.
Structural and surrounding metallic elements grounded.
Control of power loops and common mode loops.
Addition of EMI filters and ferrites on cables to either filter out or block CM
noise.
Usage of isolation techniques on data links.
Usage of balanced transmission lines and differential signalling.

Immunity tests.
Conducted common mode (CM) noise is a fact in ATLAS: systems must be designed
to cope with it. The ways CM noise is converted into differential mode (DM) noise is widely
described in the litterature. The CM noise will enter a system through all the cables (power,
input and output) and returns to its source through ground. The immunity of systems withrespect to common mode noise must be checked to insure its compatibility with the specified
compatibility level.
Conducted emissions immunity tests carried out in laboratories shall be done on
appropriate ground planes, with the same setup as for emission tests with the addition of an
injection current probe driven by an RF amplifier.
Data Links
AC

LVPS

Probe
Power Link
CM Noise

SystemUnder
Test

DAQ/DCS

Ground plane

RF Generator
RF Amplifier

Analyzer

Analyzer

The immunity test shall be done for spectrums comprised between 10kHz and 100MHz.
The most sensitive CM frequencies must first be identified. For this the DAQ system must run
continous calibration runs and record the RMS values and error rates defined in the EMC
Report, for each frequency step at fixed amplitude. An automated test setup is strongly
recommended in order to cover as much as possible the whole spectrum. The CM injected
onto the cable shall be monitored to insure that a constant intensity is injected over the whole
spectrum. From this, a diagram of the RMS values or Error Rates versus frequency is
obtained. The most critical frequency is retained.
In a second phase, the RF generator is set at a fixed frequency corresponding to themost sensitive one, and amplitude is swept up until the compatibility limit of the system isreached.
20

The initial tracking spectrum, the most sensituve frequency, and the CM current
compatibility limit are reported in the EMC report.
Tests on AC powerline shall be carried out with an appropriate LISN to normalize theAC plug impedance and allow for repeatible measurements independently of the plug used.

3.10. Electromagnetic survey.
The electromagnetic environment of the experimental area will remain unknown until
the experiment is fully commissioned. Then, it is not possible to set radiated immunity limits
beforehand. On the other hand, it sounds unpractical to establish arbitrary radiated emissions
limits for systems whose immunity is difficult to measure due to its large dimensions: radiatedemissions and immunity tests shall be done in anechoic chambers, which is unrealistic. Also,
because shielded cables and faraday cages are extensively used, and because the frequency
range of emissions won’t exceed 500MHz (excepting gigabit link drivers and receivers withlimited radiated coverage), it can be stated that a system is subject to the radiated emissions it
creates.
Therefore, measurements carried out on testbeams can be assimilated to system level
radiated immunity tests. Emission measurements cannot be performed because of lack ofappropriate anechoic chambers.
Still, for longer term, it will result extremely useful to know the electromagnetic
environment of ATLAS, in particular for maintenance and upgrade of the systems, and for
future experiments. For this, an electromagnetic survey will be carried out at fixed places in
the cavern, with monopole and dipole antennas.

21

4.

References[1]

ATLAS Policy on Grounding and Power Distribution.
http://www.cern.ch/Atlas/GROUPS/FRONTEND/WWW/atlas_gn.pdf[2]

Technical Report – Electromagnetic Compatibility (EMC) – IEC 61000-5-2:1997
http://atlas.web.cern.ch/Atlas/GROUPS/FRONTEND/EMC/Archive/IEC%2061000-502%20{Ed1.0}.pdfhttp://atlas.web.cern.ch/Atlas/GROUPS/FRONTEND/EMC/Archive/IEC%2061000-502%20%7bEd1.0%7d.pdf[3]

Liaisons equipotentielles et Protections Electromagnetiques – LHC-E-EN-0001
https://edms.cern.ch/file/358369/1.0/LHC-E-EN-0001-10-00.pdf

[4]
[5]

Installation Electriques a Basse Tension – NFC 15-100.
CERN Electrical Code C1.
http://edms.cern.ch/file/335725/LAST_RELEASED/C1_E.pdf[6]

Safety Instruction 33.
http://edms.cern.ch/file/335799/LAST_RELEASED/IS33_E.pdf[7]

On Grounding as seen by TIS.
http://tis-server.cern.ch/tis/gs/Meetings/External/LHC_Safety/Safety_Topics/Docs/Grounding.pdf[8]

EMC at CERN.
http://szoncso.home.cern.ch/szoncso/EMC/[9]

Grounding and Shielding in Facilities
Ralph Morrison, Warren H. Lewis;WILEY & SONS 1990.

[10]

Noise Reduction Techniques in Electronic Systems – Second Edition
Henry W. Ott; WILEY & SONS 1988.

[11]

Grounding and Shielding Techniques for Large Scale Experiments
Marvin Johnson, Fermilab
Proceedings of the 8th Workshop on Electronics for the LHC
http://lhc-electronics-workshop.web.cern.ch/LHC-electronics-workshop/2002/PLENARY.htm[12]

EMC in High Energy Physics
Fritz Szoncso, CERN
Proceedings of the 2nd Workshop on Electronics for the LHC
http://s.home.cern.ch/s/szoncso/www/EMC/EMC4proc961015.pdf[13]Cable Shielding for Electromagnetic Compatibility.
Anatolyy Tsaliovich, Chapman & Hall, 1995.

[14]

Comaptibilite Electromagnetique.
Deuxieme edition, Ecoles Polytechniques de Lausanne et de Zurich.
Presse Polytechnique Romande, 1985.

[15]“EMI Filter Design and Stability Assesment of DC Voltage Distribution based on
switched Converters”. Arteche et al., LEB Workshop 2001, pp.353-357.

22

[16]

“Electromagnetic Compatibility for CMS Experiment”. Arteche et al, LEB Workshop
2002, pp.191-196.

[17]“Effect of CM and DM Noise Propagation in LV Distribution Cables”. Arteche, F;
Rivettta, C. LEB Workshop 2003, pp.380-385.

[18]“Noise Immunity Analysis of the Forward Hadron Calorimeter Front End
Electronics”. Rivetta et al, LEB Workshop 2002, pp.197-202.

[19]“EMC Immunity Test Results of HCAL FEE”. Arteche et al, LECC 2003, pp.358-363.

[20]“Noise Susceptibility Analysis of the HF Front End Electronics for the CMS HighEnergy Experiment”. Arteche, F; Rivetta, C. IEEE International Symposium on
Electromagnetic Compatibility, 2003, pp. 718-723.

[21]

Safety Instruction 48.
http://ts-dep.web.cern.ch/ts-dep/groups/hdo/pdf/IS48.pdfhttp://ts-dep.web.cern.ch/ts-dep/groups/hdo/pdf/IS48.pdf

23

Annex 1: Systems.
1. Pixel detector.
2. Semiconductor Tracker (SCT).
3. Transition Radiation Tracker (TRT)
4. Central Solenoid.
5. Endcap Toroid.
6. Barrel Toroid.
7. Liquid Argon Barrel Calorimeter.
8. Liquid Argon Endcap Calorimeters.
9. Tile Calorimeter.
10. Muon Drift Tube Chambers.
11. Cathode Strip Chambers.
12. Resistive Plate Chambers.
13. Thin Gap Chambers.

24

5.

Annex 2. About international standards.
Equipment purchased within the EU shall be compliant to some of the following
standards depending on the type of equipment (non exhaustive list).
EN 50081-2
EN 50082-2
EN 55011
EN 55022
EN 61000-2-4
EN 61000-3-2
EN 61000-4-1
EN 61000-4-3
EN 61000-4-6
EN 61000-6-2
EN 61000-6-4
EN 60950
NF C 15-100

Electromagnetic Compatibility – Generic emissions standard - Part 2: industrial
environment. (superseeded by EN 61000-6-2).
Electromagnetic Compatibility – Generic immunity standard - Part 2: industrial
environment (superseeded by EN 61000-6-4).
Industrial, scientific and medical (ISM) radio-frequency equipment - Radio
disturbance characteristics - Limits and methods of measurement.
Information technology equipment – Radio disturbance characteristics - Limits andmethods of measurement.
Electromagnetic compatibility (EMC) -- Part 2-4: Environment - Compatibility levels
in industrial plants for low-frequency conducted disturbances.
Electromagnetic compatibility (EMC) -- Part 3-2: Limits - Limits for harmonic
current emissions (equipment input current up to and including 16 A per phase)
Electromagnetic compatibility (EMC) -- Part 4-1: Testing and measurement
techniques - Overview of IEC 61000-4 series
Electromagnetic compatibility (EMC) -- Part 4-3: Testing and measurement
techniques - Radiated, radio-frequency, electromagnetic field immunity test
Electromagnetic compatibility (EMC) -- Part 4-6: Testing and measurement
techniques - Immunity to conducted disturbances, induced by radio-frequency fields
Electromagnetic compatibility (EMC) -- Part 6-2: Generic standards - Immunity forindustrial environments
Electromagnetic compatibility (EMC) -- Part 6-4: Generic standards - Emission
standard for industrial environments
Safety of information technology equipment
Low voltage french standard.

25