Grounding Grounds Common reference for the circuit Safety

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Grounding • Grounds: – Common reference for the circuit – Safety Black White Green

Grounding • Grounds: – Common reference for the circuit – Safety Black White Green Add independent safety ground • What is the potential problem of grounding? – Improper grounding may induce noise on the transmission lines Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 1

Grounding • Problem: Faraday’s Law of Induction Avoid ground loops Ground loop current Winter

Grounding • Problem: Faraday’s Law of Induction Avoid ground loops Ground loop current Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 2

Spatial Dependence Within a cabinet vs. Between two buildings D Winter 2005 ECE 766

Spatial Dependence Within a cabinet vs. Between two buildings D Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 3

Shielding Techniques Metal Box Relative voltages inside the metal box are always equal Noise

Shielding Techniques Metal Box Relative voltages inside the metal box are always equal Noise Source C 3 C 1 C 2 Short this impedance Connect the shield to the signal ground to reduce feedback effects induced by the shield. Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 4

Where to Ground the Shield? AC loop through signal wire AC loop through shield

Where to Ground the Shield? AC loop through signal wire AC loop through shield C Noise Voltage Shield should be connected to the earth ground at input reference. What if we interconnect two devices in different buildings? Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 5

Long Paths • Problem: Two distant, connected chassis grounded at different points may carry

Long Paths • Problem: Two distant, connected chassis grounded at different points may carry large currents Break the chassis connection • Solutions: – Use larger signals to increase SNR – Use light as medium • Fiber optic link • Optical isolators (phototransistor and LED in a pack) – Use balanced (double-ended, differential) connections Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 6

Balanced Connections + - Noise Voltage • Both chassis are isolated electrically • Noise

Balanced Connections + - Noise Voltage • Both chassis are isolated electrically • Noise induced on both lines • Signal carried on each line: s(t) and –s(t) – Differential mode gain = – Common mode gain = – Differential mode gain >> common mode gain Winter 2005 ECE 766 Computer Interfacing and Protocols 07 - 7

Crosstalk due to Bad Grounds Resistance of bad ground Ideal Winter 2005 ECE Model

Crosstalk due to Bad Grounds Resistance of bad ground Ideal Winter 2005 ECE Model of Actual ECE 766 Computer Interfacing and Protocols 07 - 8

UTP Revisited • Faraday’s Law of Induction: . A • Direction of the induced

UTP Revisited • Faraday’s Law of Induction: . A • Direction of the induced current. A/4 Winter 2005 ECE -A/4 ECE 766 Computer Interfacing and Protocols -A/4 07 - 9

Chapter 7 The Grounds for Arguments Grounds EvidenceChapter 7 The Grounds for Arguments Grounds Evidence
Toulmin Evidence Grounds Reason Warrant Assumption Evidence GroundsToulmin Evidence Grounds Reason Warrant Assumption Evidence Grounds
4 Grounding implementation in bunker areas Grounding Implementation4 Grounding implementation in bunker areas Grounding Implementation
Equipotential Grounding Procedures Protective Grounding Training Purpose ofEquipotential Grounding Procedures Protective Grounding Training Purpose of
1 1 Introduction Grounding and Electrical Infrastructure Grounding1 1 Introduction Grounding and Electrical Infrastructure Grounding
Visual Grounding Problem Definition Visual Grounding Referring ExpressionVisual Grounding Problem Definition Visual Grounding Referring Expression
3 Grounding implementation at the instruments cave Grounding3 Grounding implementation at the instruments cave Grounding
GROUNDING 101 GROUNDING 101 WHY DO WE GROUNDGROUNDING 101 GROUNDING 101 WHY DO WE GROUND