Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Inductive Coupling Effects
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Control Systems > Inductive Coupling Effects

Inductive Coupling Effects

Last updated: July 29, 2019 9:27 am
Editorial Staff
Control Systems
1 Comment
Share
5 Min Read
SHARE

Magnetic fields, unlike electric fields, are exceedingly difficult to completely shield. Magnetic flux lines do not terminate, but rather loop. Thus, one cannot “stop” a magnetic field, only re-direct its path.

A common method for magnetically shielding a sensitive instrument is to encapsulate it in an enclosure made of some material having an extremely high magnetic permeability (μ): a shell offering much easier passage of magnetic flux lines than air.

A material often used for this application is mu-metal, or μ-metal, so named for its excellent magnetic permeability:

Inductive Coupling Effects

Inductive Field Effects

This sort of shielding is impractical for protecting signal cables from inductive coupling, as mumetal is rather expensive and must be layered relatively thick in order to provide a sufficiently low-reluctance path to shunt most of the external magnetic flux lines.

The most practical method of granting magnetic field immunity to a signal cable follows the differential signaling method discussed in the electric field de-coupling section, with a twist (literally). If we twist a pair of wires rather than allow them to lie along parallel straight lines, the effects of electromagnetic induction are vastly minimized.

The reason this works is best illustrated by drawing a differential signal circuit with two thick wires, drawn first with no twist at all. Suppose the magnetic field shown here (with three flux lines entering the wire loop) happens to be increasing in strength at the moment in time captured by the illustration:

Inductive Coupling

According to Lenz’s Law, a current will be induced in the wire loop in such a polarity as to oppose the increase in external field strength. In other words, the induced current tries to “fight” the imposed field to maintain zero net change.

According to the right-hand rule of electromagnetism (tracing current in conventional flow notation), the induced current must travel in a counter-clockwise direction as viewed from above the wire loop in order to generate a magnetic field opposing the rise of the external magnetic field.

This induced current works against the DC current produced by the sensor, detracting from the signal received at the instrument.

When the external magnetic field strength diminishes, then builds in the opposite direction, the induced current will reverse. Thus, as the AC magnetic field oscillates, the induced current will also oscillate in the circuit, causing AC “noise” voltage to appear at the measuring instrument. This is precisely the effect we wish to mitigate.

Immediately we see a remarkable difference between noise voltage induced by a magnetic field versus noise voltage induced by an electric field: whereas capacitively-coupled noise was always common-mode, here we see inductively-coupled noise as differential

(This is not to say magnetic fields cannot induce common-mode noise voltage: on the contrary, magnetic fields are capable of inducing voltage in any electrically-conductive loop. For this reason, both differential and ground-referenced signals are susceptible to interference by magnetic fields).

If we twist the wires so as to create a series of loops instead of one large loop, we will see that the inductive effects of the external magnetic field tend to cancel:

How Twisted Wire Cables Eliminates Noise Voltage

Not all the lines of flux go through the same loop. Each loop represents a reversal of direction for current in the instrument signal circuit, and so the direction of magnetically-induced current in one loop directly opposes the direction of magnetically-induced current in the next.

So long as the loops are sufficient in number and spaced close together, the net effect will be complete and total opposition between all induced currents, with the result of no net induced current and therefore no AC “noise” voltage appearing at the instrument.

In order to enjoy the benefits of magnetic and electric field rejection, instrument cables are generally manufactured as twisted, shielded pairs. The twists guard against magnetic (inductive) interference, while the grounded shield guards against electric (capacitive) interference.

If multiple wire pairs are twisted within the same cable, the twist rates of each pair may be made different so as to avoid magnetic coupling from pair to pair (An example of this is the UTP (Unshielded, Twisted Pair) cabling used for Ethernet digital networks, where four pairs of wires having different twist rates are enclosed within the same cable sheath.).

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

What is the DDE Protocol?
MODBUS ASCII Communication Protocol Explained
20 Most Common Types of Cyber Attacks
PID Controllers with Output High Select Logic
Difference Between Optical Fibre and Coaxial Cable
Recognizing an Over-Tuned PID Controller by Phase Shift
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
1 Comment
  • Gulam Ahmed Raza says:
    August 2, 2017 at 3:32 pm

    Super knowledge site sir

    Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

What is an Electrical Drive? Types, Advantages, Disadvantages
Difference Between Batch Process and Continuous Process
Control Systems Interview Questions & Answers
Basics of Motion Controllers
Types of System Architecture used in Industrial Automation
Example of Feedback System
Understanding a Process Control Loop
Derivative (Rate) Control Theory

Keep Learning

Split range control scheme

Overview of Split Range Control

Hardwired IO and Serial IO - Differences Explained

Hardwired I/O and Serial I/O – Differences Explained

Practical Process Control System Questions

Process Control Loop Testing

Alarm and Trip Documentation

PLC Alarm and Trip Documentation

System Architecture in Industrial Automation

How to Design a System Architecture in Industrial Automation?

PID Tuning recommendations

PID Tuning Recommendations based on Process Dynamics

VFD Commissioning and Testing Procedure

VFD Commissioning and Testing Procedure (Variable Frequency Drive)

Ziegler-Nichols Open Loop Tuning Procedure

Ziegler-Nichols Open Loop Tuning Procedure

Learn More

Supervisory Control

Supervisory Control

HVDC transmission compared to HVAC transmission

Comparison of HVDC transmission and HVAC transmission

Pressure Gauge Problems

Pressure Gauge Problems

Pressure Switch Construction

Basics of Pressure switches

HVAC Multiple Choice Questions

HVAC Multiple Choice Questions

Do You Need a VPN on Your Home Computer?

Do You Need a VPN on Your Home Computer?

What is a Spool valve

What is a Spool Valve? – Types, Configurations, Applications

Car Parking System PLC Program Example

Schneider Electric: Car Parking System with Calculations in PLC

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?