US Patent 7,791,353 B2
Introduction
Simple Circuit Concepts
Transmission lines
Faraday's law
Near and far fields
Spurious coupling mechanisms
- Direct conduction
- Capacitive coupling -problem
- Capacitive coupling -fixing
- Inductive coupling-problem
- Inductive coupling -fixing by twisted
- Inductive coupling -fixing by coax
- Electromagnetic pickup
- Examples
- Safety & star grounding
- Gnd loop resistance, inductance
- Low frequency behavior
- High frequency behavior
- Troubleshooting
- Methods for removing
Inductive coupling - fixing by using coaxial cable
Coaxial cable has the property of producing no magnetic field external to the cable because in the region outside the cable the return (shield) conductor, being coaxial with the signal conductor, produces a magnetic field equal and opposite to that produced by the signal conductor. Thus, if coaxial cable is used, no magnetic field is produced that could link another circuit. Caox can be used on the signal circuit to make it immune from stray fields and on other circuits to prevent them from producing stray fields. The immunity of the signal circuit can be seen in Fig. 9 by considering imaginary surfaces (dashed lines) on either side of the center conductor with a cut in the outer conductor. If the coax in Fig. 9 is unrolled, then the direction of the two surfaces (indicated by small black arrows) are opposite so any external magnetic field (blue lines) penetrating the coax produces no net flux.
Coaxial cable has the property of producing no magnetic field external to the cable because in the region outside the cable the return (shield) conductor, being coaxial with the signal conductor, produces a magnetic field equal and opposite to that produced by the signal conductor. Thus, if coaxial cable is used, no magnetic field is produced that could link another circuit. Caox can be used on the signal circuit to make it immune from stray fields and on other circuits to prevent them from producing stray fields. The immunity of the signal circuit can be seen in Fig. 9 by considering imaginary surfaces (dashed lines) on either side of the center conductor with a cut in the outer conductor. If the coax in Fig. 9 is unrolled, then the direction of the two surfaces (indicated by small black arrows) are opposite so any external magnetic field (blue lines) penetrating the coax produces no net flux.
Find ground loops fast!
-eliminate electical interference, fix star grounding
-eliminate electical interference, fix star grounding
US Patent 7,791,353 B2
Figure 9 Cross-section of coaxial cable: surface between center and outer conductor points up on right hand side (small black arrow) and down on left hand side so magnetic field (blue) from external circuit produces no net linked flux.
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