Download TN-C DC Scheme

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