Rockwell Automation System Design User Manual

System Design for Control of Electrical Noise

Reference Manual

Important User Information

Because of the variety of uses for the products described in this publication, those responsible for the application and use of this control equipment must satisfy themselves that all necessary steps have been taken to assure that each application and use meets all performance and safety requirements, including any applicable laws, regulations, codes and standards.

The illustrations, charts, sample programs and layout examples shown in this guide are intended solely for purposes of example. Since there are many variables and requirements associated with any particular installation, Allen-Bradley or liability (to include intellectual property liability) for actual use based upon the examples shown in this publication.

Allen-Bradley publication SGI-1.1, Safety Guidelines for the

Application, Installation and Maintenance of Solid-State Control

(available from your local Allen-Bradley office), describes some important differences between solid-state equipment and electromechanical devices that should be taken into consideration when applying products such as those described in this publication.

Reproduction of the contents of this copyrighted publication, in whole or part, without written permission of Rockwell Automation, is prohibited.



does not assume responsibility

Throughout this manual we use notes to make you aware of safety considerations:

ATTENTION

Identifies information about practices or circumstances that can lead to personal injury or death, property damage or economic loss.

Attention statements help you to:

•

identify a hazard

•

avoid a hazard

•

recognize the consequences

IMPORTANT

Allen-Bradley is a registered trademark of Rockwell Automation.

Identifies information that is critical for successful application and understanding of the product.

Preface

Electrical Noise Control Overview

Who Should Use this Manual . . . . . . . . . . . . . . . . . . . . . . . P-1

Purpose of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . P-1

Contents of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . P-2

Related Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . P-3

Conventions Used in this Manual . . . . . . . . . . . . . . . . . . . . P-3

Chapter 1

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

What is Electrical Noise?. . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

Understanding the Need for Electrical Noise Control . . . . . . 1-1

CE Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

Best Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Noise Control Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Noise Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Noise Victims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Coupling Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Conducted Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Mutual Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Electromagnetic Radiation. . . . . . . . . . . . . . . . . . . . . . . 1-6

Solutions for Reducing Noise . . . . . . . . . . . . . . . . . . . . . . . 1-6

Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Measuring Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

High Frequency (HF) Bonding

Chapter 2

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Understanding the Source of Electrical Noise . . . . . . . . . . . 2-1

Noise Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Noise Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

The Ground Plane Principle . . . . . . . . . . . . . . . . . . . . . 2-3

Extending the Ground Plane Principle. . . . . . . . . . . . . . 2-5

Grounding a PCB to the Drive Chassis . . . . . . . . . . . . . 2-5

Noise Solutions Using the Ground Plane Principle . . . . . . . 2-6

Grounding to the Component Mounting Panel. . . . . . . . 2-6

Doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

Adjacent Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Grid and Raised Floor. . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Mezzanine Floor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Machine Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

New Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

Existing Buildings. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

Limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

Grounding (Safety Earth) . . . . . . . . . . . . . . . . . . . . . . . . . 2-14

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ii Table of Contents

Segregating Sources and Victims

Shielding Wires, Cables, and Components

Chapter 3

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Understanding the Segregation Concept . . . . . . . . . . . . . . . 3-1

Noise Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Ensuring CE Compliance at Build Time . . . . . . . . . . . . . 3-2

Zone Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

Component Categories . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

Routing Wires and Cables Within a Panel . . . . . . . . . . . . . . 3-4

Wire and Cable Categories . . . . . . . . . . . . . . . . . . . . . . 3-6

Routing System Wires and Cables Between Panels. . . . . . . . 3-8

Chapter 4

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

Understanding the Shielding Concept . . . . . . . . . . . . . . . . . 4-1

Ferrite Sleeves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Ferrite Sleeve Limitations. . . . . . . . . . . . . . . . . . . . . . . . 4-4

Mixing Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

Filtering Noise

Contact Suppression

Chapter 5

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

Understanding the Filtering Concept . . . . . . . . . . . . . . . . . . 5-1

Commercial AC Line Filters for Low Voltage Circuits . . . 5-1

General Purpose 0-24V ac/dc Filters . . . . . . . . . . . . . . . 5-2

Filter Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

Performance Test Set-up . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Ultrasonic Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

Xenon Flashing Beacons (strobe lights). . . . . . . . . . . . . . . . 5-5

AC Line Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

Earth Leakage/Ground Fault . . . . . . . . . . . . . . . . . . . . . 5-6

Chapter 6

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

Understanding Contact Suppression for AC Circuits . . . . . . . 6-1

Methods of AC Contact Suppression . . . . . . . . . . . . . . . 6-2

Understanding Contact Suppression for 24V dc Circuits . . . . 6-3

Methods of DC Contact Suppression . . . . . . . . . . . . . . . 6-3

Contact Suppression Effects . . . . . . . . . . . . . . . . . . . . . . . . 6-4

Power Distribution

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Chapter 7

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Understanding Noise in Power Wiring . . . . . . . . . . . . . . . . 7-1

Three-Phase Power Supplies. . . . . . . . . . . . . . . . . . . . . . . . 7-1

Line Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

Single Phase Power Supplies . . . . . . . . . . . . . . . . . . . . . . . 7-4

Motor Wiring

High Speed Registration Inputs

Table of Contents iii

24V dc Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

24V dc Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

24V dc PSU Zoning Methods. . . . . . . . . . . . . . . . . . . . . 7-5

Linear PSU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

Special Applications for 24V dc PSUs . . . . . . . . . . . . . 7-11

Chapter 8

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

Understanding Noise in Motor Power Wiring . . . . . . . . . . . 8-1

Shielding Motor Power Cables . . . . . . . . . . . . . . . . . . . . . . 8-2

Grounding Motor Power Cable Shields . . . . . . . . . . . . . . . . 8-2

Applying Ferrite Sleeves. . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

Splicing Motor Power Cables . . . . . . . . . . . . . . . . . . . . . . . 8-3

Handling Excess Cable. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4

Installing Long Motor Cables . . . . . . . . . . . . . . . . . . . . . . . 8-4

Chapter 9

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

Understanding Registration Inputs . . . . . . . . . . . . . . . . . . . 9-1

Noise Reduction Methods. . . . . . . . . . . . . . . . . . . . . . . . . . 9-2

Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2

Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2

Shared Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2

Dedicated Power Supply. . . . . . . . . . . . . . . . . . . . . . . . 9-4

Detection Device Mounting. . . . . . . . . . . . . . . . . . . . . . 9-4

Proximity Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5

Signal Noise Filter Options. . . . . . . . . . . . . . . . . . . . . . . . . 9-5

Single Voltage Input (24V or 5V). . . . . . . . . . . . . . . . . . 9-6

Dual Voltage Inputs (24V or 5V) . . . . . . . . . . . . . . . . . . 9-7

Registration Error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8

Error Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9

Software Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9

Encoders

Measuring Noise Reduction Effectiveness

Chapter 10

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Understanding Encoders . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Noise Reduction Methods. . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Driver Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2

Power Supply Wiring Options . . . . . . . . . . . . . . . . . . . . . 10-3

Chapter 11

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1

Understanding Noise Measurement. . . . . . . . . . . . . . . . . . 11-1

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iv Table of Contents

Methods for Measuring Noise . . . . . . . . . . . . . . . . . . . . . . 11-1

Measuring Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2

Oscilloscope Specifications . . . . . . . . . . . . . . . . . . . . . 11-2

Oscilloscope Settings for Measuring Noise Peaks . . . . . 11-2

E-Field Sniffing Method. . . . . . . . . . . . . . . . . . . . . . . . 11-3

H-Field Sniffing Method . . . . . . . . . . . . . . . . . . . . . . . 11-4

Direct Voltage Measurement Method . . . . . . . . . . . . . . 11-4

Grounding Your Probe (reference ground) . . . . . . . . . 11-6

Ground Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7

Differential Measurements . . . . . . . . . . . . . . . . . . . . . . 11-7

Scope Probe Lead Extension . . . . . . . . . . . . . . . . . . . . 11-9

Checking Your Method for Effectiveness . . . . . . . . . . . 11-9

Identifying the Noise Source . . . . . . . . . . . . . . . . . . . 11-10

Intermittent Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-10

General Guidelines for Measuring Noise . . . . . . . . . . . . . 11-10

What are Acceptable Noise Levels? . . . . . . . . . . . . . . 11-10

Field Strength Meters . . . . . . . . . . . . . . . . . . . . . . . . 11-11

Monitoring for Noise. . . . . . . . . . . . . . . . . . . . . . . . . 11-11

Noise Control Supplement

Appendix A

Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Grounding Cable Shields . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Pigtails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Clamping at the Circular Section . . . . . . . . . . . . . . . . . . A-2

Wire Segregation Test Results . . . . . . . . . . . . . . . . . . . . . . . A-5

Test Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7

Switch-Mode DC Power Supplies . . . . . . . . . . . . . . . . . . . . A-8

Background Information . . . . . . . . . . . . . . . . . . . . . . . . A-8

Grounding the Common . . . . . . . . . . . . . . . . . . . . . . . . A-9

DC Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-11

Positioning the PSU within the Panel . . . . . . . . . . . . . . A-11

AC Line Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-12

Using Separate DC Power Supplies . . . . . . . . . . . . . . . A-12

Using a Dynamic Braking Contactor . . . . . . . . . . . . . . . . . A-13

Reducing Dynamic Braking Circuit Noise. . . . . . . . . . . A-14

Bonding Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-15

Wire Forms an Antenna . . . . . . . . . . . . . . . . . . . . . . . A-15

Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-15

Noise Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-16

EMC Product Suppliers

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Appendix B

EMC Product Suppliers. . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Preface

Read this preface to familiarize yourself with the rest of the manual. The preface covers the following topics:

• Who should use this manual

• The purpose of this manual

• Contents of this manual

• Related documentation

• Conventions used in this manual

• Allen-Bradley support

Who Should Use this Manual

Purpose of this Manual

Use this manual if you are responsible for the circuit design and layout of wiring panels or the installation and mounting of Allen-Bradley products. Specifically, the following disciplines should be included:

• Circuit designers

• Panel layout designers

• Panel builders and electricians

• Electrical technicians

In addition, you should have an understanding of:

• Drive control and basic electronics

• Appropriate electrical codes

This manual outlines the practices which minimize the possibility of noise-related failures and that comply with noise regulations. It gives you an overview of how electrical noise is generated (sources), how the noise interferes with routine operation of drive equipment (victims), and examples of how to effectively control noise.

This manual applies in general to Allen-Bradley drives products. For information on specific Allen-Bradley motion products refer to Noise Control Supplement - Motion Products Reference Manual (publication GMC-RM002x-EN-P).

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P-2 Preface

Contents of this Manual

The contents of this manual are described in the table below.

Chapter Title Contents

Preface Describes the purpose, background, and

scope of this manual. Also specifies the audience for whom this manual is intended.

1 Electrical Noise Control

Overview

2 High Frequency (HF) Bonding Describes the ground plane principle and

3 Segregating Sources and

Victims

4 Shielding Wires, Cables, and

Components

5 Filtering Noise Describes how low-pass filters and ferrite

Provides a brief understanding of the need for electrical noise control, how noise affects system performance, noise coupling methods, and solutions.

provides techniques for bonding devices, panels, machines, floors, doors, and buildings.

Describes how establishing zones within your system for noise sensitive or noise generating components can reduce electrical noise coupling.

Describes how using shielded cable or steel shields can reduce electrical noise.

sleeves can reduce electrical noise.

6 Contact Suppression Describes how contact suppressors for

relays and various other switches can reduce electrical noise.

7 Power Distribution Describes bonding, segregating, shielding,

and filtering techniques for use when routing AC and DC power.

8 Motor Wiring Describes shielding, grounding, and

splicing techniques for use with motor wiring.

9 High Speed Registration

Inputs

10 Encoders Describes bonding, segregating, shielding,

11 Measuring Noise Reduction

Effectiveness

Appendix A Noise Control Supplement Provides background information on

Appendix B EMC Product Suppliers Provides a list of EMC product suppliers,

Describes how wiring sensitive to electrical noise benefits from proper noise reduction strategies.

and filtering techniques for use with encoders.

Describes the equipment, methods, and various guidelines for measuring noise levels and noise reduction effectiveness.

specific topics related to electrical noise control.

the products they offer, and internet website.

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Preface P-3

Conventions Used in this Manual

The following conventions are used throughout this manual:

• Bulleted lists such as this one provide information, not procedural

steps.

• Numbered lists provide sequential steps or hierarchical

information.

• Words that you type or select appear in bold.

• When we refer you to another location, the section or chapter

name appears in italics.

N/A

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P-4 Preface

Publication GMC-RM001A-EN-P — July 2001

Electrical Noise Control Overview

Chapter

Chapter Objectives

What is Electrical Noise?

This chapter provides a brief understanding of the need for electrical noise control, how noise affects system performance, noise coupling methods and solutions. This chapter covers the following topics:

• What is electrical noise

• Understanding the need for electrical noise control

• Noise control basics

• Coupling mechanisms

• Solutions for reducing noise

• Implementation

• Measuring effectiveness

Electrical noise is voltage spikes, generated by the routine operation of selected system components (sources), that interfere (due to a coupling mechanism) with the routine operation of other selected system components (victims).

Understanding the Need for

In Europe, a system must satisfy EMC regulations. It must also work reliably without suffering from noise-induced failures.

Electrical Noise Control

CE Compliance

Most equipment is CE marked. This means it is certified to be compliant with European Directives which comprise two main requirements:

• Potential noise sources must be limited in noise output to a

• Potential victims of noise must be hardened to withstand a higher

specified level.

noise level.

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1-2 Electrical Noise Control Overview

In both cases, equipment must be installed to manufacturers recommendations to achieve compliance. The frequency range covered is 150kHz to 1GHz, though the upper limit is likely to be raised as operation frequencies increase.

Despite this, a CE compliant industrial drive system may still suffer functional failures due to electrical noise. Additional measures are often necessary to prevent noise from being coupled between source and victim. The frequency range involved in system failures is generally confined between 200kHz and 10MHz.

Best Practices

Most industrial control products do not utilize high frequencies directly, but they can generate them in the form of noise. Logic circuits are affected by this noise, so you need to be able to control it.

Noise Control Basics

Because it is far less expensive to apply noise control measures during system installation than it is to redesign and fix a malfunctioning system, we recommend you implement the best-practice procedures described in this document.

If basic measures are implemented rigorously, a reliable system should result. However, if just one wire is routed incorrectly or a filter is missed, it may be enough to cause problems. Experience shows that it is very difficult to ensure that these measures are applied 100% of the time. If all possible measures are taken (incorporating redundancy), the system is likely to be more tolerant of minor mistakes in implementation.

A typical industrial control system will contain a mixture of noise sources and potential victims. Problems are caused when a coupling mechanism is introduced.

Noise Sources

Publication GMC-RM001A-EN-P — July 2001

Typical noise sources include:

• Mechanically switched inductive loads create intense intermittent

noise.

• PWM drive power outputs create intense continuous noise.

• Switch-mode DC power supplies can create continuous noise.

Electrical Noise Control Overview 1-3

• Microprocessor clocks can generate high levels of noise at the

clock frequency and its harmonics.

• Contact switching.

Of the noise sources listed above, only contact switching noise can be reduced at the source by the system builder.

Refer to the figure below for an example of a typical noise source.

Figure 1.1 Switch-Mode Power Supply Noise Measurement

Line

Filter

+24V

24V dc PSU

DC common

Ground Plane - conductive metal panel

No load connected

Noise voltage measured here

Refer to Figure 1.2 for an example of six volt noise spikes from a typical 24V dc power supply. The spikes usually contain frequencies above 10 MHz.

Figure 1.2 Switch-Mode Power Supply Noise

10V

-2

-4

-6

6.0V pk

-8

-10V

-10123456789

Sitop Power 20 with 3 phase input - no load

Common Mode Noise +24 Volts to Backplane

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1-4 Electrical Noise Control Overview

Noise Victims

Typical noise victims include the following:

• Microprocessor controlled devices

• Analog devices

• Encoder and registration interfaces

Refer to Figure 1.3 for an example of a typical victim.

Figure 1.3 A victim TTL gate is easily triggered

Noisy circuit carrying 6V spikes

comprising mainly 10 MHz

5V TTL gate

Coupling Mechanisms

100 pF = 200 Ω

50 Ω

Signal Source (zero impedance)

Refer to the section Capacitance below for an explanation of the 200 ohm impedance. Generally, most potential victims are better protected than this.

@ 10 MHz

Victim TTL gate receives 1.2V spikes

The source noise level and the victim’s sensitivity are normally outside the control of the system designer so that it is necessary to concentrate on the transmission of noise between them.

The coupling mechanism is the means by which electrical noise interferes with the routine operation of equipment. This section describes the four common coupling mechanisms for electrical noise transmission.

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Conducted Noise

Noise is conducted directly by system power wiring. A common route for conducted noise is the 24V dc distribution wiring.

Electrical Noise Control Overview 1-5

Capacitance

At radio frequencies (RF) the capacitance between two adjacent wires is significant. Two insulated wires touching each other and only 1.0 meter (39.0 in.) long form a capacitance of approximately 100 pF (Pico Farads). At 10 MHz the impedance is only 200 ohms.

Fortunately, the effect reduces as the square of the separation distance. Refer to Figure 1.4 for an example of capacitive coupling.

Figure 1.4 Capacitive Coupling

Stray

capacitance

Circuit A

Separation distance

Circuit B

Mutual Inductance

At radio frequencies (RF) the inductance of a straight wire is significant. A length of wire 1.0 meter (39 in.) has an inductance of

approximately 1.0 ohms.

Two adjacent wires have mutual inductance forming a transformer. Fortunately, the effect reduces as the square of the separation distance. Refer to Figure 1.5 for an example of inductive coupling.

Figure 1.5 Inductive Coupling

H (Micro Henry). At 10 MHz the impedance is 60

Stray

inductance

Circuit A

Magnetic coupling

Circuit B

Separation distance

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1-6 Electrical Noise Control Overview

Electromagnetic Radiation

An example of electromagnetic radiation is radio transmission. Industrial control wiring systems are large, wideband antenna which radiate noise signals to the world. These signals (together with conducted noise) are the primary target of the European regulations, but rarely cause system malfunctions.

Solutions for Reducing Noise

This method: In this

category:

HF (high frequency) Bonding

Segregation Coupling

Shielding Coupling

Filtering Coupling

Coupling Reduction

Reduction

Noise reduction solutions are categorized as coupling reduction and source reduction. There are four main methods used to reduce the coupling of noise between source and victim. However, contact suppression is the only source reduction technique that can be directly applied by the system builder. Refer to the table below for a summary.

Is defined as: For more

information refer to:

Maintaining all

metalwork at the same electrical potential. This method is low cost and the basis for all other methods. It works by ensuring all equipment chassis are at the same potential at all

The chapter High

Frequency (HF) Bonding.

frequencies. If different potentials exist the voltage difference is seen as common-mode noise on all interconnecting wiring.

Separating sources and victims of electrical noise into zones. Noise coupling reduces with the square of separation distance. Zoning is zero cost (within limits).

Using shielded cable and steel barriers (Faraday cage effect) to reduce electrical noise. Because of its relatively high cost, shielding is used with discretion.

Using low-pass filters to attenuate RF noise. Relatively low cost but impractical for every wire.

The chapter

Segregating Sources and Victims.

The chapter Shielding Wires, Cables, and Components.

The chapter Filtering Noise.

Contact Suppression

Source Reduction

Adding contact suppression to mechanical switches to reduce noise. Generally, the one noise source directly influenced by the system builder.

Publication GMC-RM001A-EN-P — July 2001

The chapter Contact Suppression.

Electrical Noise Control Overview 1-7

Implementation

This application: Is defined as: For more

Routing AC and DC power

Routing motor power cables

Wiring high speed registration inputs

Routing encoder power cables

Applying bonding, segregating, shielding, and filtering techniques to AC and DC power supplies and the associated wiring.

Applying shielding, grounding, and splicing techniques to motor power cable installation.

Applying all the noise reduction methods available to improve the performance of noise sensitive wiring.

Applying bonding, segregating, shielding, and filtering techniques to encoder installation.

Measuring Effectiveness

Implementation involves applying the methods summarized in the table on page 1-6 to the applications as shown in the table below.

information refer to:

The chapter Power Distribution.

The chapter Motor Wiring.

The chapter High Speed Registration Inputs.

The chapter Encoders.

Measuring noise reduction effectiveness involves using an oscilloscope to test for noise during implementation. It also involves monitoring for noise after implementation should updates to the system affect system performance.

This application: Is defined as: For more

information refer to:

Measuring effectiveness

Testing for electrical noise during implementation, identifying the sources of noise, determining acceptable noise levels, and monitoring for noise on an on-going basis.

The chapter

Measuring Noise Reduction Effectiveness.

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1-8 Electrical Noise Control Overview

Publication GMC-RM001A-EN-P — July 2001

High Frequency (HF) Bonding

Chapter

Chapter Objectives

Understanding the Source of Electrical Noise

This chapter describes the ground plane principle and techniques to extend the ground plane to devices, panels, machines, floors, doors, and buildings. This chapter covers the following topics:

• Understanding the source of electrical noise

• Noise solutions using a ground plane

• Grounding (safety earth)

The most common source of electrical noise is due to switching of PWM output stages.

Two examples of how noise is generated by a drive system are given on the following pages.

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2-2 High Frequency (HF) Bonding

Noise Example 1

The transistors impose a 600V step change in the wire B (typically less than 200nS). Stray capacitance A charges very rapidly causing a current spike. This is the dominant noise source in PWM (Pulse Width Modulated) drive systems.

The current circulates through stray capacitance C, bonding impedance D, bonding impedance E, bonding impedance F, and back to stray capacitance A. A voltage spike will appear between motor frame and machine structure (Vd), between machine structure and the panel (Ve) and between the panel and drive chassis (Vf).

The circuit of an encoder mounted on the motor will then have a voltage spike of amplitude Vd + Ve relative to the panel and to any input circuit on the panel, potentially a noise victim.

The noise voltages are proportional to the impedance of the bonds (voltage = current x impedance). If these are reduced to zero, no voltage will appear between encoder and panel.

Figure 2.1 Switching noise affecting encoder signal

Drive

Heatsink (connected to chassis)

IMPORTANT

Panel

The quality of bonding techniques applied during installation directly affects the noise voltages

+600V dc

Stray

capacitance

Transistor block

DC common

Impedance due to

poor bonding

between system components.

Motor

Windings

Encoder

Machine Structure

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High Frequency (HF) Bonding 2-3

Noise Example 2

Stray capacitance I charges very rapidly. Current circulates via stray capacitances H, bond G, bond F, and A. In this way, a voltage Vf + Vg is developed between the drive chassis and true-ground.

Any remote equipment grounded to this true-ground and wired to the drive will have this noise voltage imposed upon its incoming signal.

Figure 2.2 Switching noise affecting incoming power

AC line

Stray capacitance

to ground

Drive

Heatsink (connected to chassis)

Impedance due to poor bonding

Panel

+600V dc

Stray capacitance

Transistor block

DC common

Many other noise sources exist in a typical system and the advantage of good bonding holds true for all.

The Ground Plane Principle

The purpose of High Frequency (HF) bonding is to present a defined low impedance path for HF noise currents returning to their source.

IMPORTANT

Most textbooks on radio frequency (RF) techniques describe the ground plane (GP) as the ultimate ground reference and an absolute requirement for controlling RF current paths.

Noise current must and will return to source. If a safe path is not provided, it may return via victim wiring and cause circuits to malfunction.

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2-4 High Frequency (HF) Bonding

The ground plane principle was originally developed by printed circuit board (PCB) designers for high frequency circuits. In multi-layer PCBs a minimum of two copper layers are used with one being designated the ground or common. This layer covers as large an area as possible and each IC common is tied directly to it. In addition, each IC Vss (+5V) pin is decoupled by a 0.1

F capacitor to the ground plane as close as possible to the pin. The capacitor presents a very low impedance at RF hence any induced noise current generates minimal voltage.

The fundamental property of a ground plane is that every point on its surface is at the same potential (and zero impedance) at all frequencies. At high frequencies this is more effective than the use of single point grounding schemes. This is because wire has significant inductance at RF and just a few inches can create an unacceptable voltage drop. Refer to the section Bonding Surfaces in Appendix A for more information.

Figure 2.3 Ground plane layer in a double-sided printed circuit board

Vss pin

Vdd pin

(common)

Ground plane

layer

Insulation

layer

Integrated Circuit

Interconnect

layer

(+5V)

Decoupling Capacitor

(Vss to ground)

Ground plane construction has proved so successful that it is now universal in PCB design for all but the most price-sensitive and low frequency circuits. Single-sided PCBs are not generally used for RF or TTL circuits.

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High Frequency (HF) Bonding 2-5

Extending the Ground Plane Principle

The same theory holds true regardless of scale, (the earth being the ultimate and literal ground plane) and can be used at control cabinet level or even building level, but requires rigorous implementation.

A ground plane does not have to be flat, but gentle curves prove more effective than sharp corners. Area is what matters. Even the outer surface of a machine structure can be used.

Grounding a PCB to the Drive Chassis

In the figure below, a PCB ground plane is extended by bonding it to the drive chassis.

Figure 2.4 PCB ground plane extended to the drive chassis

Drive

chassis

Printed circuit

board (PCB)

Guidelines for the system builder include:

PCB copper interconnection layer

PCB copper ground plane layer bonded to drive chassis

• When permitted, the control circuit common should be grounded.

• Some products do not permit grounding of the control common,

but may allow grounding to chassis via a 1.0

F, 50V ceramic

capacitor. Check your installation manual for details.

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2-6 High Frequency (HF) Bonding

Noise Solutions Using the Ground Plane Principle

In this section, examples of how to apply the ground plane principle are described.

Grounding to the Component Mounting Panel

In the example below, the drive chassis ground plane is extended to the mounting panel. The panel is made of zinc plated steel to ensure a proper bond between chassis and panel.

Figure 2.5 Drive chassis ground plane extended to the panel

Drive ground plane (chassis) bonded to panel

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Note: Where TE and PE terminals are provided, ground each

separately to the nearest point on the panel using flat braid.

Plated vs. Painted Panels

In an industrial control cabinet, the equivalent to the copper ground layer of a PCB is the mounting panel. To make use of the panel as a ground plane it must be made of zinc plated mild steel or if painted, the paint must be removed at each mounting point of every piece of metal-clad equipment (including DIN rails).

Zinc plated steel is strongly recommended due to its inherent ability to bond with the drive chassis and resist corrosion. The disadvantage with painted panels, apart from the cost in labor time to remove the

High Frequency (HF) Bonding 2-7

paint, is the difficulty in making quality control checks to verify if paint has been properly removed, and any future corrosion of the unprotected mild steel will compromise noise performance.

Plain stainless steel panels are also acceptable but are inferior to zinc plated mild steel due to their higher ohms-per-square resistance.

Though not always available, a plated cabinet frame is also highly desirable since it makes HF bonding between panel and cabinet sections more reliable.

Painted Components

Mating surfaces must be cleaned of paint and the exposed surfaces protected against corrosion with conductive paint or petroleum jelly.

Anodized Aluminum Components

Mating surfaces must be cleaned of anodizing and the exposed surfaces protected against corrosion.

EMC Filters

Filter performance depends entirely on close coupling between the filter case and the drive chassis (or other load chassis). They should be mounted as close as possible to the load and on the same panel. If a painted panel is used, short braid straps should be used to tie the two chassis together. As a temporary remedy, an effective means of coupling filter case and drive chassis is to lay a single piece of aluminum foil beneath the two chassis.

Doors

For doors 2 m (78 in.) in height, bond with two or three (three is preferred) braided straps (top, bottom, and center).

EMC seals are not normally required for industrial systems.

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2-8 High Frequency (HF) Bonding

Adjacent Panels

Bond adjacent panels by mounting multiple flat straps between the panels. As an alternative, mount a filler plate between the panels using multiple fasteners along the edges of the plate.

Figure 2.6 Panel ground plane extended to adjacent panels

Adjacent panels

bonded to extend

the ground plane

Cabinet ground plane (component mounting panel)

Ground plane extended to side panel by bonding to main panel

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High Frequency (HF) Bonding 2-9

Grid and Raised Floor

Bonding cabinet panels and machine chassis to a ground grid below a raised floor is the best possible grounding scheme and commonly used in computer mainframe installations, but rarely used in industrial environments.

Ideally the grid squares should be 1 m (39 in.) or less.

Figure 2.7 Panel ground plane extended to a grid beneath a raised floor

Machine structure used as ground plane

Cabinet ground plane (panel) bonded to floor ground plane

Copper strip laid on the floor,

(also bonded to machine structure).

Grid ground plane.

covered by a false floor

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2-10 High Frequency (HF) Bonding

Mezzanine Floor

A mezzanine floor makes a very effective ground plane if the floor panels are aluminum or galvanized steel and bonded at their edges every 1 m (39 in.) minimum. Machine structure, floor, and both panels form one large ground plane.

Figure 2.8 Panel ground plane extended to a mezzanine floor

Mezzanine floor ground plane

Cabinet ground plane (panel) bonded to Mezzanine floor ground plane

Machine structure

bonded to floor

Machine structure used as ground plane

Machine structure

bonded to floor

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High Frequency (HF) Bonding 2-11

Machine Structure

If the machine structure covers a large portion of the system area and is constructed of a conductive material with all sections closely bonded, then it too will form an excellent ground plane. Care should be taken to ensure paint is removed at the bonds and the connections protected against corrosion.

Figure 2.9 Panel ground plane extended to the machine structure

Machine structure used as ground plane

bonded to structure ground plane by

Panel ground plane

clean and dirty wireways

Bond the panel(s) to the machine structure as tight as possible, but if this proves difficult, construct a low impedance path using the following guidelines:

• Use a zinc-plated tray, as wide as practical, and join sections by

overlapping with several fasteners across the width. The perforations will not reduce performance (refer to Figure 2.10).

• EMC trunking (plated at joint surfaces with conductive gaskets)

also makes a good bond.

• Short and wide is the requirement for any HF bonding material.

Panel(s) should be located as close to the machine structure as practical and the bond should be firmly attached at both the machine structure and the control panel (not the cabinet outer panels).

• Multiple trays/trunking are better.

Note that copper wire safety earth bonding is still required. Refer to the section Grounding (Safety Earth) at the end of this chapter for more information.

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2-12 High Frequency (HF) Bonding

Figure 2.10 Extending the panel ground plane using cable tray

Multiple

fasteners

Zinc plated

steel main

panel

Same width

Note: A ground plane does not have to be flat.

Must be directly bonded here and at the machine structure

Zinc plated

steel cable tray

(wider is better)

New Buildings

In new installations it is possible to specify that the structural steel columns are bonded together beneath the floor. This is similar in concept to the special floor grid shown earlier (refer to Figure 2.7), but inferior due to the large grid squares.

Cabinet ground plane (panel)

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The panels are bonded by a flat strip or braid to the nearest steel column. The floor, machine structure, and panels form a large, but relatively ill-defined ground plane.

Figure 2.11 Panel ground plane extended to the building

Machine structure used as ground plane Steel Column

Steel Column

bonded to nearest

building steel

Building ground plane.

Copper strip laid into the floor

bonding columns together.

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