When designing electronics especially for sensing and control, preventing EMI noise due to Grounding is important to ensure reliable quality signals

1. Analyzing the Basics of EMC &
EMI using Current Signal Flows
and Grounding
&
Case Studies
Dr Tan Guan Hong
1 December 2020
1

2. Kirchoff’s Law
Σ = 0 , this applies for both DC and
AC currents at various
frequencies
Analyse DC currents differently from AC
Analyse AC currents at 1 MHz is different from
AC currents at 100 MHz ! Split the Currents in its
individual Frequency Spectrum and then Analyse
I2
I1
I3
I4
I1-4
Fundamental
2

3. Kirchoff’s Law for AC Current
For AC currents, the Fun begins !
I1
I3
I2
Fundamental
3
Σ Send out I1 = 1 A, Return back I2 = - 1 A
I1-2
=0
If sends out I1 = 1 A, Return back I2 = - 0.9 A
means there I3 = -0.1 A back somewhere !
If sends out I1 = Sin(ωt), only return I2 = - Sin(ωt + ϕ) with a Phase shift.
Means this is not balanced already.
There is an I3 which is I3 = -I1 -I2 = - Sin(ωt) + Sin(ωt + ϕ)
Send out I1 = Sin(ωt), Must return I2 = - Sin(ωt)
- Sin(ωt) + Sin(ωt+ϕ) = - Sin(ωt) + Sin(ωt) Cos(ϕ) + Cos(ωt) Sin (ϕ)
I3 =0 , only if ϕ = 0 . This means the Waveform must be in Anti-Phase to
cancel each other out. If not, then there is still a leakage coming else
where

4. Simple DC Voltage and Resistor
Simple DC + AC Voltage and Resistor
DC
DC
AC
DC
AC Simple DC + AC Voltage, Series Resistor
& Inductor, Parallel Resistor & Capacitor
Fundamental
4
Signal from DC to DC + AC with Resistive Load
Resistive with Capacitive and Inductive Loads
Moving from a Simple Wire to a High Frequencies Transmission Line

5. Time to Frequency Domain Transformation
A Spike Voltage when analyze in Frequency Domain
is a Wide Band of Many Sine Wave Frequencies !
Multiple
Sine
Waves
Fundamental
5
Time Frequency

6. 50Hz
150Hz
1 MHz
100 MHz
Time to Frequency Domain
0Hz
Time to Frequency
Time to Frequency
Fundamental
6

7. Need to Analyse the DC and AC Current paths
Fundamental
240 Vac 12 Vac
Pre
Amp
Power
Amp
= DC AC
+
Need to keep the High Ripple Currents return path earlier
7
= DC + AC
100 Hz
50 Hz

8. Equivalent circuit of a DC Motor
The Motor is not a simple DC device. It has
Resistance (R) , Inductance (L) and Back EMF Voltage Ec from by the Rotating Mass
Hence the Current I a is NO longer a simple DC current one way flow device !
Motor

9. Chassis Grounding
Using the Metal Chassis as a return current path is
actually is an indeterminate current return path !
Analyse a Motor power by a Power Supply with
Metal Chassis as a return current path
EMI
Approved
Device
EMI
Approved
Device
Fundamental
9
With different metals, Galvanic corrosion will occur over time !
Cable

10. Motor power by a Power Supply with a well define
return current path
Chassis as shield against external interference is better
Motor Carbon Brush Arcing is a
Current Pulsing Source Generator !
EMI
Approved
Device
EMI
Approved
Device
Fundamental
10
Cable
Cable

11. https://www.thoughtco.com/table-of-electrical-resistivity-conductivity-608499
Material Ohm – meter (x10 -8)
Copper 1.68
Aluminum 2.82
Iron 10.0
Lead 22.0
Titanium 42.0
Stainless Steel 69.0
Resistance / meter of Metals
Assuming L=100 , A= 1, same diameter cable
carrying 100 A,
If both cables are Copper, then the Electric Field
will cross to each other, means no leakages
0V
-0.168 mV 0V
+0.168mV
0V
0V
+0.168mV
-69.0 mV
Fundamental
11
-0.168mV
For Copper, Voltage Drops is 0.168 mV
Stainless Steel is 6.9 mV (41x of Cu !). Means it
leaks to elsewhere !

12. Identify :-
Modules for Sensing, Control and Power
Know Internal Module Grounding of Inputs, Outputs and Power Supplies
Wiring flow diagram for Analog and Digital Sensors with +V and GND return
wires
Wiring flow diagram for Power Modules, Motor Drivers, DC-DC Converters for
+V and GND
Work out Wiring clustering within the Analog signal paths and Power & GND
paths
Work out Wiring clustering within the Digital signal paths and Power & GND
paths
Work out Wiring clustering within the Power Modules. Motor Drivers and DC-DC
Converters Supply & GND
Only then you decide how to interconnect the GNDs
between wiring clusters 12
Design Process

13. Wiring of AC
Current flow
Wiring of DC
Current flow
Wiring of High
power DC
current flow
Wiring of Low
power DC
current flow
Wiring of High
Frequency AC Signal
flow
Wiring of Analog
Signal flow
Wiring of Digital
Signal flow
Wiring
Diagram for
Electrical
Connectivity
Electrically
inter-connected
Electrically
inter-connected
13
Design Process

14. Controller
Module
with
Analog,
Digital with
Power
input
Start from identifying each module for inter-connections and their pin Inputs / outputs
Vs
GND
Analog Sensor
input
Digital Control
Output
48 V DC
to 12V DC
Converter
Is
Is
Power On
Surge
Steady
State
Peak
Operation
12 A 3A 6A
2 sec Continuous 60 sec
Power On
Surge
Steady
State
Peak
Operation
12 A 3A 6A
2 sec Continuous 60 sec
Analog
Sensor
Output
module
Digital
Controller
Power
Driver
2 uA
1 uA
1 uA
1 uA
2 uA
High
Power
Motor
48 V DC
Power
Pack
Which GND Connect ? 14

15. Controller
Module
with
Analog,
Digital with
Power
input
Strip other components out and start analyzing Analog Signals from basic for clarity
Vs
GND 0V
Analog Sensor
input
48 V DC
to 12V DC
Converter
Is
IX
Power On
Surge
Steady
State
Peak
Operation
12 A 3A 6A
2 sec Continuous 60 sec
Analog
Sensor
Output
module
2 uA
2 uA
0.01 Ω
0.01 Ω
0.01 Ω V5-4= - 3A x 0.01
Use GND as True 0 V
Is
Is
1
2
3
4
Sensor output = 100 mV
Sensor Analog Input is read at
V1-4 =
V1-2
+ V2-3 + V3-4
5
V1-4 = V1-2 + V2-3 + V3-5 + V5-4
Grounding via 3 to 4
a) If now GROUNDING via 3 to 5
= - 30 mV
V1-4 = V2-3 + V5-4
= 100 + (- 30) = 70 mV for 3A
= 100 mV
100 + (- 60) = 40 mV for 6A
=
For 6 As
This means that when the Current goes
up, the sensor readings goes down !
V1-4
V2-3
15
=
V1-4
V2-3
As V1-2
V3-4 =
As - V1-2
V3-5 =
=
0.02 uV
0.02 uV Negligible
=

16. Analog
Controller
Module
with
Power
input
Internally
Grounding
Vs
GND
Analog
Control Output
48 V DC
to 12V DC
Converter
Is
Is
Analog Controller
Internal Grounding
1 uA
1 uA
1 uA
0.01 Ω / 6A
1
2
3
4 5
6
V1-4 = V1-2 + V2-3 + V3-5
Grounding via 3 to 5 , if we already 6 to 5 as Power Ground
=
100 mV
- V5-4 (Direction of Current is – ve)
V2-3
- 60 mV , V2-3 = 160 mV
16
Strip other components out and
start analyzing Analog Signals
from basic for clarity
Do not use software compensation for
hardware offset as Hardware problems
must be solve by hardware solutions !
Can be non-linear

17. Voltage
Speed
Speed Sensor gives 100 mV @ 25 km/hr
Comparison of Analog and Digital Devices
Physical World
is Analog
Amplifier
Analog
Speed
Sensor If now due to DC Off-set voltage of +20 mV due
to GROUNDING noise, the computer now
thinks that AV is traveling at 30 km/ hr !
Speed Sensor
Calibration
Curve Depending on the DC Off-set current direction,
the it can also cause – 20 mV , i.e. 20 km / hr
instead
With A Digital Speed Sensor 25 km/hr is
now in Binary Data
1
0
DC Off-set affect the Logic voltage
also, but DOES NOT affect output
due to Digital Rising-Falling Edge
Logic Detection method 17

18. Analog
Controller
Module
with
Power
input
Internally
Grounding
Vs
GND
Analog
Control Output
48 V DC
to 12V DC
Converter
Is
Is
Analog Controller
Internal Grounding
1 uA
0.01 Ω / 6A
1
2
3
4 5
6
Use of Isolator Modules for Input and Output
18

19. 19
Internally
Grounding
Internally
Grounding
Error in Diagram ! Is it
connected or Not ?
Case Study:Paravan

20. 20
@ Full throttle Bus2 paddle is 4280 mV
( Near to +5000 mV supply)
@ Full Throttle Error Difference is small, Compare to when Idle. Other additional Ground Voltages ?
159mV -55 mV
-78mV
324 mV
Simulated such that Output = Input Voltages ?
Case Study:Paravan

21. 21
+5V
+5V
GND
GND
Gas Pedal
Sensor has 2
potentiometers
Internally
Grounding Use ohm meter to
check for GND as all
are connected
Power GND is NOT Signal
GND ! Signal GND is for
Voltage Referencing,
Power GND is for Power
Current Return
Isolated
DC-DC
Converter
Internally
Grounding
Use DC-DC Converter
to isolate Power
supply and Power
GND
Case Study:Paravan

22. 22
+5V
+5V
GND
GND
Gas Pedal
Sensor has 2
potentiometers
Internally
Grounding
Power GND is NOT Signal
GND ! Signal GND is for
Voltage Referencing,
Power GND is for Power
Current Return
A
mA
mA
A
Internally
Grounding
10 Ω
Case Study:Paravan

23. 23
Internally
Grounding
Internally
Grounding
Case Study:Paravan
Analyze the GND
Wiring Loop

24. OEM Engine
Control Unit
24
Paravan
Gas
Interface
GND
GND
GND
GND
5A
2A 1A
Using Kirchoff’s current Law to analyze possible current flows
Gas Pedal
potentiometer
7A
0.01 Ω
0.01 Ω
1A
1A
6A
Ground Loop in the Original Paravan Proposal
Re-trace current flow to its basic current flow diagram
0.01 Ω
This 1 A flowing through 0.01 Ω is now 10 mV
Case Study:Paravan
GND

25. OEM Engine
Control Unit
25
Paravan
Gas
Interface
GND
GND
GND
GND
6A
2A
1A
1 mA
10 Ω
If the potentiometer current is taking 1 mA, @ 10 Ω, the voltage drop is only 10 mV
The lowest voltage @ Idle is 400 mV, the Error is only 2.5 %
Gas Pedal
potentiometer
7A
2 A across 10 Ω is 20 V ! , the 2A will take the path of least resistance of 0.01 Ω
0.01 Ω
0.01 Ω
0.01 Ω
+
1A
2A
1A
1 mA
Case Study:Paravan
5A
5A

26. Case Study 1
Vehicle Intercom System Noise
• Intercom System, Government Furbished Equipment (GFE) Item
• Engine noise pick up through CVC helmet when engine operating
• Noise level increase when engine rpm increase
• Intercom boxes’ mechanical mounting points not painted (suspect grounding of
signal through body fastening points)
• Alternator ground connected to chassis return
• Noise at CVC helmet reduce significantly when Intercom boxes are electrically
isolated from vehicle chassis.
Master
Control
Station
Power
Distribution
Box
Power
and
chassis
return
FFCS
VHF
Radio
Audio
signal
CVC
Helmet
Antenna
• Alternator Return Ground
is always Noisy Chassis
Ground
• Use Ohm meter to check
if Audio Ground
connected to Intercom
Box mechanical
mounting points
• Use Teflon isolators
• Try using 10 ohm to
divert noisy current away
Case Study:IntercomNoise
26

27. Power
Distribution
Box
Noisy Power and Chassis return
Audio Signal
Headphone
Audio GND
Amplifier
Power GND
Microphone
Metal
Shielding
Box
In
In
Another
Current
Return path
using
Enclosure as
a Noisy
current return
path
The metal chassis now is a
Radiation Antenna surface !
To the high gain circuits
Possible Cause and Effect due to
Grounding and Chassis Metal
Case Study:IntercomNoise
27

28. 28
Following Case Studies are related to Grounding for
Electrical Voltage Spike Discharge
Functionality
Performance
Reliability
Convenience
Price
Noise
Spike Voltages
Cabling
Isolators

29. Case Study 2
Temperature Sensor Failure
+VE (10V)
-VE (0V)
Analogue
Signal (0V to
5V)
Pin A
Pin B
Pin C
Temperature Sensor
• Multiple temperature sensor failures (out of range) have
occurred in vehicles in the field.
• The sensor manufacturer suspects that the cause of the faults
is latching related to voltage transients between the sensor
chassis (body) and the sensor common (-VE), or noise
voltage imposed on the analogue signal wire.
• Usually multiple failures
are Design issue. Trace
where the voltage
transients are coming from
• If there are Voltage
Transient between sensor
chassis body and Sensor
Common (-VE). Use a
Transient Voltage
Suppressor (Open if
Voltage is less than 15 V,
short if Voltage exceeds
20V).
Case Study:Transient
29

30. Case Study 3
Temperature Sensor Failure
• PDB provides power to Controller at 24V DC; the Controller
steps down to 10V DC to the temperature sensors mounted
on the Motor.
• The Motor is mounted to the vehicle chassis.
• PDB’s Battery negative and the generator negative is
connected to vehicle chassis.
• It was discovered 28V ground, Analogue sensor ground and
Vehicle chassis all connected together
GEN
(-) (+)
PDB
28V
0V
Controller
28V
0V
To other loads
10V
0V
Signal
DC/DC Sensor
Motor
• Usually Motors have Back
EMF transients and can
cause high voltage spikes
• 0V of Controller and
Sensor don’t need to
connect to Chassis at all.
As these are for Voltage
Referencing only.
• Add 10 ohm to reference
and still break the current
loop
Internally
Grounding
Internally
Grounding
Case Study:Transient
30

31. 31
PDB
https://www.ti.com/lit/an/snva681a/snva681a.pdf?ts=1597300868669&ref_url=https%253A%252F%252Fwww.google.co
m%252F#:~:text=A%20load%20dump%20occurs%20when,to%20400%20ms%20to%20decay%22.
A Load Dump occurs when the Load to
which a generator is delivering current is
abruptly disconnected. In Automotive
electronics, this applies to disconnecting
a battery while it is being charged by the
alternator. It can be "as high as 120 V
and may take up to 400 ms to decay".
Case Study:Transient

32. 32
Case Study:Transient
Motors do create Back EMF spikes
Use of Diode to
suppress Reverse
Voltage back EMF
spikes

33. 33
Case Study:Transient
Need to Analyze Current
Flows when using Current
shunts with Multiple GNDs,
Wire by Wire !

34. DC Power Supply
Computer
1
2
6
4
5
3
Vs
Is
Is
In this circuit, it is a resistive circuit
C: PDB Input V
B: ML PC Voltage
A: ML PC Current
Now the
Computer has
a switching AC
Generator !
Ia
Ia
Ib
Ic
Ic
Ia Ib
Ic
= +
Even current probe measurements can mis-lead you in the diagnostic of
current flow analysis as it depends on where you probe. Voltage is used
more often, as it is easier to understand, but no enough for trouble
shooting ! 34

35. Self Generated Internal
Surge Source
by a Motor
Motor

36. Equivalent circuit of a DC Motor
The Motor is not a simple DC device. It has
Resistance (R) , Inductance (L) and Back EMF Voltage Ec from by the Rotating Mass
Hence the Current I a is NO longer a simple DC current one way flow device !
Motor

37. A simple DC Supply powering an Inductor
When the Switch S1 is open, there is a Back Emf Generated by that Inductor
https://www.electronics-tutorials.ws/inductor/inductor.html
Inductive Load

38. Current and Voltage in an Inductor Inductive Load

39. • 4 Amp DC passes through a 0.5 H
solenoid coil.
• Switch is opened within 10 mS
• Solenoid current flowing through the
coil dropped to 0 Amp
V L = L di = 0.5 (4-0) = 200 Volts
dt 0.01
Why switching Inductor cause high voltage surge ?
Inductive Load

40. 40
Options for Over coming GROUNDING
Challenges by using more Isolation Modules
Considerations of using Isolation Modules due to Poor
Wiring and Grounding Design
Additional Expense
Mounting space
Extra cabling of Modules
More components to Fail !
Power consumption increase
Good Design to
Prevent having
such Challenges
is Best

41. Thank you for
your attention
Dr Tan Guan Hong
Email: tan.guanhong@stengg.com
Mobile: 97271973
After 31 December 2020
Email: drtangh@gmail.com
Confidential and Copyright