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CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Noise Isolation
Keeping the Gremlins Out
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
How noise gets into your circuits
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Key Characteristics of the noise sourceVoltage
Current
Frequency
Distance from the victim
‘High’ voltage Strong electric field Capacitive coupling‘High dV/dt Capacitive coupling
‘High’ current Strong magnetic field Inductive coupling
‘High’ frequency Radiation Radiative coupling
Distance = 0 Direct contact Conductive couplingDistance > wavelength Probably Radiative
0 < Distance < Wavelength Capacitive or Inductive
dT
dVCI
Not For Us
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Key Characteristics of the noise sourceVoltage
Current
Frequency
Distance from the victim
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
What is the most likely coupling mechanism for
Fluorescent light noise
Arc welding noise
Digital clock noise
Capacitive
Capacitive
Inductive
High Voltage
High Current
High dv/dt
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
What is the most likely coupling mechanism for
Fluorescent light noise
Arc welding noise
Digital clock noise
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Conductive coupling
Motor
Sensor
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
More conductive coupling+12V +5V
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
How should I wire these up?
12V 7.5V
Motor
HC11
+G
G G
G
G+
+ +
+
Sensor
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Which waveform must be conductively coupled?
Why?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Identifying characteristics of conductive coupling
Metallic contact required
Unaffected by people or cable movement
Non-zero average value for the waveform
Techniques to reduce conductive coupling
Break the conductive contact
Use filtering
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Identifying characteristics of conductive coupling
Metallic contact required
Unaffected by people or cable movement
Techniques to reduce conductive coupling
Break the conductive contact
Use filtering
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Capacitively coupled noise
Simplified circuit
Coupling capacitance
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Physical Representation of capacitively coupled noise
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Equivalent circuit for capacitively coupled noise
1212
21212
)(/1
)]/([V
CCRj
CCCjV
G
GN
If
If)(
1
212 GCCjR
)(
1
212 GCCjR
1212
12
)(V
CC
CV
GN
112VRCjVN
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Reducing Capacitively coupled noise
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Reducing Capacitively coupled noiseShield
Connect the shield to return the noise current to the source
How many connections to the shield are required?
Position the shield to intercept the noise current
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Summary of capacitive noise reduction techniques
Reduce capacitive noise coupling by
1. Reducing coupling capacitance
2. Reducing circuit impedance
3. Using shielding
Capacitive shielding requires
1. Proper shield location
2. Correct shield connection
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Summary of capacitive noise reduction techniques
Reduce capacitive noise coupling by
Capacitive shielding requires
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Isolation
Why do you need it?
How do you get it?
Conductive noise
Large voltage differential
Provide fault isolation (Safety)
Minimize leakage currents
Magnetic coupling
Optical coupling
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Isolation
Why do you need it?
How do you get it?
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Isolation via magnetic coupling
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
PCB mount miniature relays
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Reed Relay construction
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
Optical Isolation
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS
68HC11 PS2501Opto-Isolator
L-298H-Bridge
Create a design to connect
