Inductive Coupling in Analog Instrumentation and How to Reduce It ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

Inductive Coupling in Analog Instrumentation and How to Reduce It

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When a wire carries an electrical current it produces a magnetic field; if this wire is in the vicinity of another wire also carrying electrical current or signal, the magnetic field they produce interact with one another resulting in noise voltage being induced in the wires. This is the principle through which inductive coupling takes place in instrumentation signal cable wiring

As we already know, Inductance is a property intrinsic to any conductor, whereby energy is stored in the magnetic field formed by current through the wire. Mutual inductance existing between parallel wires forms a “bridge” whereby an AC current through one wire is able to induce an AC voltage along the length of another wire. This become even more pronounced if we have power cables and instrument signal cables going through the same duct or conduit.
A simple way to reduce inductive signal coupling is to simply separate conductors carrying incompatible signals. This is why electrical power conductors and instrument signal cables are almost never found in the same conduit or in the same duct work together.
The most practical method of reducing inductive coupling and granting magnetic field immunity to instrument signal wires is to twist a pair of wires rather than allow them to lie along parallel straight lines. This greatly reduces the effects of electromagnetic induction.

Electromagnetic induction is reduced because when the wires are twisted so as to create a series of loops instead of one large loop, the inductive effects of the external magnetic field tend to cancel out thereby reducing the induced noise voltage on the instrument signal wires due to the external magnetic field.

Go back to Ways to Reduce Capacitive Coupling in instrumentation signals
Or go to Ground Loops and Impedance Coupling: Causes and Reduction