Any training class is a considerable investment in terms of cost and your time. You can’t afford to waste any of your precious time and you need to attend something that is useful and improves your productivity. After five years of presentation throughout the world, this workshop is well polished, practical and relevant.
The aim of this workshop is to help you identify, design, prevent and fix common EMI/EMC problems with a focus on earthing and shielding techniques. Learning how to fix earthing and shielding problems on the job can be very expensive and frustrating. Although it must be noted that most of the principles involved are simple, this workshop will give you the tools to approach earthing and shielding issues in a logical and systematic way.
This workshop focuses on the issues of interest to you if you are working in design, operation or maintenance of analog or digital systems involving sensors, data acquisition, process control, cables, signal processing, programmable logic controllers, power distribution, high speed logic etc.
The circuit board layout section concentrates on design and layout of circuits and components on a printed circuit board. The overall focus is on useful design and systems issues; not about regulations and standards. The idea is that you will take this material back with you to your work and apply the key principles immediately to your design and troubleshooting challenges.
WHO SHOULD ATTEND?
Building service designers
CAD managers
Consulting engineers
Data systems planners and managers
Design engineers
Electrical and instrumentation technicians
Electrical contractors
Electrical engineers
Electrical inspectors
Electricians
EMC specialists
Electronics and systems engineers and technicians
Instrumentation and control engineers
Logic designers
Maintenance engineers
Mechanical engineers
Power system protection and control engineers
Printed circuit board designers
Project engineers
Safety professionals
Signal integrity specialists
Technical managers
Test engineers
MORE INFORMATION: http://www.idc-online.com/content/practical-shielding-emcemi-noise-reduction-earthing-and-circuit-board-layout-66
2. Coupling Paths: Sources & Victims
Source Equipment
Radiated, cable to cable
case to case
Conducted through
common earth
impedance
Victim Equipment
Peripheral
Radiated,
Input
Radiated, case
to mains cable
Conducted via
common mains
impedance
External mains interference
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
7. Receptors
RF, Communication, Radar, Telemetry Receivers etc.
(Anything intended for RF reception or using tuned circuits)
Digital Electronics, Software
(Anything that can be upset by shifting logic levels, timing or clock
disturbances, memory or data line toggling etc.)
Analog Electronics
(Any sensitive circuit that can amplify, rectify, saturate, shift levels etc.)
Sensitive Materials - Ammunition, Fuel
(Anything at risk of burning, exploding)
Human Beings - biological hazard
(Anything living)
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
9. Conductive Connection
(Common Impedance Coupling)
System B
Load Input
Vin
V Connection has inductance, L
System B input = (Vin+V)
where V~ -L.d IL /dt
System A
IL
Input
Vin
Load
System A System B
IL
Problem
Solution
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
10. Magnetic Induction
Load
System A
IL
System B
Vin
Rs
Zin
Vn
Mutual Inductance, M
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
11. Electrostatic Coupling
Vin
System B
Load
System A
IL
Rs
Zin
Vn
Stray or parasitic
capacitance
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
12. Real World Coupling
Noise Source
Magnetic
Induction
Victim
Electrostatic
(Capacitive)
Coupling
Posible Ground Loop or
Common Impedance Coupling
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
13. Mutual C & L vs Lead Spacing
0,25 1,25
0,20
0,15
0,10
0,05
1,00
0,75
0,5
0,25
D D
1 mm
1,6 mm
C
Mutual
Capacitance
(pF/cm) M
(nH/cm)
Mutual Inductance
1 2 4 8 10 20 40 80 100
D (mm)
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
14. Coupling via the supply network
50
ohms 50 μH
SOURCE VICTIM
Attenuation30
dB/km
20
10
Distribution system
Cable only
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
15. Electromagnetic fields
V
D (m)
E-field I
R (m)
H-field
Propagation
V
E-field
H-field
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
16. Rayleigh/Maxwell near/far fields
E a1/r3, H a1/r2
Electric field
predominates
Near field impedance
anywhere in this region
H a1/r3, E a1/r2
Magnetic field
predominates
Plane wave
Z = 377 ohms
Far field
Transition area
0,1 1 10
10 k
1 k
Zwave
100
10
Distance from source, normalised to l/ 2p
Frequency Max dimension
D (m)
Rayleigh
d = 2D2/l (m)
Maxwell
d = l/2p (m)
10 MHz
30 MHz
2
2
2
0,5
0,5
2
0,5
100 MHz
300 MHz
1 GHz
0,267 4,77
0,8
0,167
2,67
0,5
8,0
1,67
1,59
0,477
0,477
0,159
0,159
0,0477
Rayleigh & Maxwell
distances for
transition to
far field
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
18. Radiated Emissions from PCB
(Differential Mode)
Signal current
Loop of area ‘A’
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
20. Coupling Paths - Conducted Emissions
SMPS L
N
E
Signal cable
CIRCUIT
ICME
0 V
CC
VNsupply
CS CS
IDM
Measurement
Measurement
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
21. Susceptibility to Radiated Field Coupling
E
Victim
Field coupling to cable
induces common mode
current at input
Possible standing wave in enclosure:
creates susceptibility/emission peaks
Field coupling to
PCB induces
differential mode
currents in circuit
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
24. Transient Frequency
Type of
area
Transients/
hour
Industrial
Commercial
Domestic
Laboratory
17,5
2,8
0,6
2,3
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
25. Electrostatic Discharge
Coupling paths likely to be:
• Stray capacitance
• Case bonding
• Track or wiring inductance due to magnetic fields
generated in the discharge
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
26. Automotive Transients
Alternator load dump
100 ms 200 ms 300 ms
Inductive switching
10 μs 20 μs 30 μs
5 ms 10 ms 15 ms
Alternator field decay
80 V
14 V
VP
-0,2.VP
14 V
-80 V
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
27. Supply Voltage Phenomena
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
28. Supply voltage phenomena - important?
1 ms 3 ms 20 ms 500 ms 10 s
500%
400%
300%
200%
140%
120%
70%
40%
0,2 ms
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
29. DO YOU WANT TO KNOW MORE?
If you are interested in further training or information,
please visit:
http://idc-online.com/slideshare
Technology www.idc-online.com/slideshare Technology TTrraaiinniinngg tthhaatt Wwoorrkkss
Editor's Notes
Electromagnetic Interference requires two parties: a source, and a victim. Any electronic device has the potential to radiate or conduct emissions, and at the same time be susceptible to them itself. Some problems may exist where the victim is also the source.
Understanding of the mechanisms by which this takes place is essential to solving EMC problems.
To ensure compatibility between one item of equipment and any other in a given electromagnetic environment requires a comprehensive understanding of the ways in which this source to victim coupling is possible. The slide above outlines the ways in which this can happen.
Keep in mind that some of the paths only exist because of the parameters which are not taken into account - the inductance and capacitance of cables, for example.
EMI works like this. Always a noise source, a coupling path and a receptor.
The solution for reducing interference can be at the source, path or receptor.
Noise sources are everywhere.
Above is a list of considerations when changing the coupling between source and victim.
Receptors everywhere!
Any EMI problem will involve any or a combination of the above coupling mechanisms.
A minor re-routing can often eliminate a problem by removing a common conductor, which we are inclined to forget has resistance, inductance and capacitance whether we like it or not.
AC current in a conductor creates a magnetic field. This can couple with a nearby conductor and induce a current in that conductor. This usually happens where there are large and/or fast variations in current (i.e. high di/dt).
Note that there is no need for a common ground for this to take place - it can happen between isolated circuits.
One conductor can be affected by a changing voltage on another. The extent of this depends on the ratio of impedances between the load and the source.
The source impedance will be determined by the distance between conductors, their effective areas and the composition of whatever is between them (dielectric).
Electrostatic (capacitive) coupling usually happens where there are large and/or fast variations in voltage (i.e. high dv/dt).
A combination of coupling mechanisms exist in the real world. One type of coupling can dominate, but sometimes a combination is present.
This graph shows the effects of the spacing between conductors on their ability to couple from one circuit to another.
Although the picture above of the supply system impedance, this is in an ideal world. In reality, the impedance is determined very largely by whatever is connected to the supply. This is shown by the graph above, and makes predictions of coupling difficult.
Any conductor with an applied voltage and current will generate an electric and a magnetic field as shown.
The way in which these fields develop will be determined by the physical layout. Whether the electric or magnetic field will dominate depends on whether the current or voltage is predominant.
Radiated emissions can be divided into ‘near field’ and ‘far field’. In the near field, separate electric and magnetic fields exist. Which one will predominate depends on the source impedance as shown above. It is important to understand this, because they are measured differently and different measures are used to counteract a magnetic or electric field.
In the far field, the two merge into a composite electromagnetic plane wave. This is often considered to take place at about one sixth of a wavelength (/2), mainly because of Maxwell. This is true of point sources, but is substantially affected by the source dimensions as shown by Rayleigh, and illustrated in the chart above.
In most cases, the wanted signal is produced in differential mode. It is also possible to have interfering signals which are induced into a conductor in differential mode, and can in turn be radiated in differential mode. Ground plays no part in this case.
The cable can also carry signals in common mode, usually interfering signals they could also be internally generated). These are referenced to ground, very often by stray capacitances and inductances and can of course be radiated as common mode signals. Common mode signals become a problem when they are converted into differential mode, and get confused with the wanted signal.
In antenna mode, currents are equally induced in the signal conductors, and in the reference plane (often happens in aircraft travelling through magnetic fields). Becomes a problem if converted to differential mode.
Although depicted as happening between two separate modules, it is very possible for this to take place on a PCB.
The circuit drawn above shows a ‘small loop antenna’ smaller than /4 at the frequency of interest. (All PCB tracks are ‘small loop antennae’ up to a few hundred MHz).
The field varies with the square of the frequency, and is directly proportional to the signal current and the loop area, and can be substantial. Keep the area small.
Cable radiation is generally common mode, which is generally far worse than differential mode.
These common mode voltages can easily arise due to poor termination, as we will see in the module on cables and connectors.
The loop area is uncontrolled, hence unpredictable. Common mode current generally needs to be under 5 µA to meet cable emission standards!
As in the drawing above, where there are high switch-mode frequencies, capacitance to ground plays a major part. This allows large common-mode voltages to develop relative to ground.
In addition, differential mode signals can appear on the supply line or the signal cable as a result of SMPS noise being getting through to the signal cable from the supply lines, or directly onto the Live and Neutral from the switching oscillator.
Coupling can take place either directly to the circuitry, or via I/O or mains lines. Common mode interference eventually translates into differential mode, and resonance within an enclosure must be regarded as a possibility.
Transients and spikes are different from continuously generated EMI. Above is a list of likely sources.
Virtually all transient wave-forms are classified in this way. There is some variation in where the second time period, T2, starts from. In this slide it is shown as being from almost the start of the rise of the wave. However, as both of these times are specified as being + or - 30% in most cases, it is difficult to see why anyone bothers!
The graph above shows the results of a study carried out on mains supply and telecom lines to record the number and amplitude of transient voltages.
These figures obviously depend on the lightning strike density in various parts of the world, and the degree of heavy load switching in the vicinity of a particular site. Particularly with lightning (but also with switching surges) the mains connection density plays a part.
This slide shows different transients that can exist in a 12V automotive system. If not designed for, 12V components will fail at these high voltages.
The supply voltage can exhibit a variety of disturbances.
The ITIC (Information Technology Industries Council) curve shown above, demonstrates the fluctuation levels and time periods which are likely to upset a PC. From this it is obvious that short-duration voltage variations can definitely affect electronic equipment.
It is just as necessary to ensure that mains-powered equipment doesn’t introduce any of these phenomena which are
voltage dips (short-duration reductions in voltage)
interruptions (complete absence of power for longer than ~ 3 s)
harmonics
unbalance (voltage differences between phases)
flicker (rapid voltage variations which are annoying as they affect incandescent lighting)
transients