CMPE 118 MECHATRONICS Noise Isolation Keeping the Gremlins Out.

CMPE 118 MECHATRONICSCMPE 118 MECHATRONICS

Noise Isolation

Keeping the Gremlins Out


How noise gets into your circuits


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


Key Characteristics of the noise sourceVoltage

Current

Frequency

Distance from the victim


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


What is the most likely coupling mechanism for

Fluorescent light noise

Arc welding noise

Digital clock noise


Conductive coupling

Motor

Sensor


More conductive coupling+12V +5V


How should I wire these up?

12V 7.5V

Motor

HC11

+G

G G

G

G+

+ +

+

Sensor


Which waveform must be conductively coupled?

Why?


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


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


Capacitively coupled noise

Simplified circuit

Coupling capacitance


Physical Representation of capacitively coupled noise


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


Reducing Capacitively coupled noise


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


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


Summary of capacitive noise reduction techniques

Reduce capacitive noise coupling by

Capacitive shielding requires


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


Isolation

Why do you need it?

How do you get it?


Isolation via magnetic coupling


PCB mount miniature relays


Reed Relay construction


Optical Isolation











68HC11 PS2501Opto-Isolator

L-298H-Bridge

Create a design to connect

CMPE 118 MECHATRONICS Noise Isolation Keeping the Gremlins Out.

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