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

iPublication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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).

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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

Publication GMC-RM001A-EN-P — July 2001

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.

Publication GMC-RM001A-EN-P — July 2001

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)

Publication GMC-RM001A-EN-P — July 2001

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.

High Frequency (HF) Bonding 2-13

Existing Buildings

The nearest building steel structures between the machine and control cabinets may be used to bond to.

If there is more than 20 m (65 ft) between the building structural steel closest to the motor and the building structural steel closest to the control panel, the ground between these two structural points should be checked and enhanced, if necessary, using at least 25 mm (1 in.) wide wire braid.

Limits

A ground plane sub-panel may only be considered part of a larger ground plane when bonded sufficiently well at RF. For this purpose wide thin strips are more effective than wire. Refer to the section Bonding Surfaces in Appendix A for more information.

≤

• Length

• Shorter = better

• Wider = better

• Thickness is not an issue. Thin is acceptable (even foil is very

effective, but fragile).

The building example shown in Figure 2.11 normally falls outside these requirements.

In cases where the maximum 10:1 bonding aspect ratio limit cannot be satisfied, a differential noise voltage must be assumed to exist between each semi-isolated ground plane. All wiring entering a ground plane will carry this noise voltage and must be dealt with at the point of entry.

A ground plane is just as effective if it is perforated or made up of a matrix of flat conductors, provided that the apertures are smaller than one quarter of the wavelength of the highest troublesome frequency.

width x 10 is the generally accepted maximum ratio.

Publication GMC-RM001A-EN-P — July 2001

2-14 High Frequency (HF) Bonding

Grounding (Safety Earth)

Grounding refers to safety grounding and although the safety ground circuit and the noise current return circuit may sometimes share the same path and components, they should be considered as totally different circuits with different requirements. The object of safety grounding/bonding is to ensure that all metalwork is at the same, ground (or Earth) potential at power frequencies.

The copper wire typically specified by regulatory bodies has little effect at the high frequencies involved in noise problems.

ATTENTION

Safety ground circuits are extremely important and all relevant local and international regulations must be adhered to and take precedence over any guidance given in this document.

Generally, safety dictates that all metal parts are connected to safety earth with separate copper wire of appropriate gauge.

Most equipment has specific provisions to connect a safety ground or PE (protective earth) directly to it.

These ground wires should be terminated directly to a bonded PE ground bar, but lengths are not important provided the ground plane strategy is followed (refer to the section The Ground Plane Principle).

Publication GMC-RM001A-EN-P — July 2001

Segregating Sources and Victims

Chapter

Chapter Objectives

Understanding the Segregation Concept

This chapter describes how establishing zones within your panel for noise sensitive or noise generating components can reduce coupling of electrical noise. This chapter covers the following topics:

• Understanding the segregation concept

• Zone classification

• Routing wires and cables within a panel

• Routing system wires and cables between panels

You can avoid many of the problems caused by noise by grouping sources and victims (along with their associated wiring) in zones according to their noise performance rather than arranging for neatness, tradition, or convenience.

Noise Zones

The three noise zones are defined in the table below.

This noise zone: Has this relative noise level:

Very-Dirty High Dirty Moderate Clean Low

This descriptive terminology (very-dirty, dirty, and clean) is chosen for maximum clarity. Most noise documents assign numbers to the zones, but there is no consistent numbering scheme. The descriptive approach allows you to see the true meaning of a zone at a glance, without having to remember a code.

Publication GMC-RM001A-EN-P — July 2001

3-2 Segregating Sources and Victims

Figure 3.1 shows how you can create three zones in a standard panel or cabinet enclosure. The very-dirty items are placed in the right/front section. The dirty items are placed behind them in the right/rear section and the least noisy (clean) items are placed in the left/rear section.

Figure 3.1 Relative position of noise zones on the panel

Main Panel or Cabinet

(top view)

Clean wireway and component

mounting section

Dirty wireway and component

mounting section

Right side divider panel

Left side and front panels (if cabinet)

Very-Dirty cable tray and component mounting

A side panel is fitted on the right to support the power cable shield clamps and any very-dirty wires, cables, or components. This leaves the main panel free for the clean and dirty zones.

Note: It is preferable to mount PLC and motion control equipment in a

separate cabinet away from power control equipment (motor starters, etc.).

Ensuring CE Compliance at Build Time

Ensuring CE compliance is aided by the use of detailed physical panel layouts, together with wiring schedules to specify precise wire routing and zone categories. Periodic checks during installation are recommended to achieve full CE compliance.

As an aid to the technicians wiring the panel, the use of grey wireways for the clean zone and black wireways for the dirty zone helps ensure proper segregation of cables. For example, this makes a communication cable running in a dirty wireway easier to see.

Zone Classification

Publication GMC-RM001A-EN-P — July 2001

You can classify each cable or device based on these two factors:

• How much noise does the cable/device generate/radiate?

• How sensitive is the device connected via the cable to electrical

noise?

Segregating Sources and Victims 3-3

Component Categories

The table below indicates which noise zone components fall into as a general reference for component segregation

Note: An X in multiple zones indicates that the component straddles

the two zones. Under these circumstances it is important to position the component in the correct orientation.

Component Very-

Dirty Clean

Dirty

PWM Drives/Amplifiers

XXX

Dynamic braking components X External Dump Resistor (unshielded) X

External Dump Resistor (shielded)

AC Line Filter X X

Dump Resistor module (metal-clad)

Switch-mode DC power supply X

Ultrasonic Transducer

Contactors X MCB X

Switched 24V dc loads

(e.g., E-stop/Piltz circuit, solenoids, relays, etc.) Encoder buffer board X PLC X Registration 24V dc supply filter X Dirty to Clean filter X X Linear DC power supply X Other 24V dc none-switched loads X Data/Communication devices X Analog devices X

The connector/terminal block locations on the drive will normally dictate the zone geometry since it normally has connections in all categories. Design zones around the drive(s).

Bond chassis to the main panel or drive chassis. Refer to the chapter High Frequency (HF) Bonding for more information.

Refer to the chapter Filtering Noise for more information.

All inductive switched loads must be suppressed. Refer to the chapter Contact Suppression for more information.

Publication GMC-RM001A-EN-P — July 2001

3-4 Segregating Sources and Victims

Routing Wires and Cables Within a Panel

The following figures provide examples of how to route clean, dirty, and very-dirty wireways or cable trays within a panel.

Figure 3.2 Routing clean and dirty cables

Main Panel

(front view)

Power

distribution

Barrier

Sensitive

equipment

PLC

PSU

Dirty Zone (black wireway)

PWM Drive

Clean Zone

(grey wireway)

Clean

Dirty

Relays

Observe the following guidelines when planning your panel layout for clean and dirty cables:

• The plated steel barrier between clean and dirty wireways allow

them to run close together.

• If dirty power is required at A, then run it via wireway B using

shielded cable. Refer to the chapter Shielding Wires, Cables, and Components for more information.

• The vertical wireway at C is not good practice as it encourages the

creation of loops. Refer to the section Minimizing Loops later in this chapter.

• The use of different colored wireways (e.g., grey for clean and

black for dirty) encourages good segregation.

Publication GMC-RM001A-EN-P — July 2001

Figure 3.3 Routing very-dirty cables

Segregating Sources and Victims 3-5

Dirty Zone

(black wireway)

Clean Zone

(grey wireway)

Main Panel (front view)

PWM

Drive

PWM

Drive

Right Side Panel

(inside view)

PWM

Drive

PWM Drive

Segregation from clean/dirty zone

Zinc plated cable tray

Drive power connections (forming bridge to cable tray)

Very-Dirty Zone (white cable tray)

Divider panel

Divider panel bonded with braided strap

to main panel (three places)

Observe the following guidelines when planning your panel layout for very-dirty cables:

• Power cables bridge across to the drive terminals from the cable

tray on the right.

• The cable tray is bonded to the divider panel using braided strap.

If no divider panel is used, then bond cable tray to main panel.

• A divider panel is used on the right to segregate very-dirty wiring

from the clean zone of the next panel to the right.

• The divider panel is bonded with braided straps to the main panel

at top, center, and bottom.

Clean and Dirty Zone

Cable tray bonded with braided strap to main/ divider panel

• Use 25.4 mm (1.0 in.) wide braided strap for bonding (preferred

method). Braided strap 12.7 mm (0.5 in.) wide is acceptable.

Publication GMC-RM001A-EN-P — July 2001

3-6 Segregating Sources and Victims

Wire and Cable Categories

The table below indicates the best zone for running cables and wires. The table also shows how the use of ferrite sleeves and shielded cable can reduce the noise effects of dirty and very-dirty wires and cables.

Note: Some items have two entries (one shielded and one not

shielded).

Zone Method

Cable and Wire Category

VeryDirty

Dirty Clean Ferrite

Sleeve

Shielded

Cable

Three Phase between Line Filter and Drive

Extended DC bus X Extended DC bus X X

PWM Drive/Inverter to Motor Power PWM Drive/Inverter to Motor Power X X PWM Drive/Inverter to Sine Wave

Filter Sine Wave Filter to Motor X CM Choke to Motor Power X CM Choke to Motor Power X X Line Terminator - Motor Power X Line Terminator - Motor Power X X External Dump Shunt Resistor X External Dump Shunt Resistor X X Contactor to AC Motor X Contactor to AC Motor X X

Publication GMC-RM001A-EN-P — July 2001

Three Phase Supply Power X Single Phase Supply Power X 24V Hydraulic/Pneumatic - solenoids X Motor Feedback Resolver X X PLC digital I/O X Dedicated Drive Inputs (except

registration) Limit Switches X Push buttons X

Cable and Wire Category

Segregating Sources and Victims 3-7

Zone Method

VeryDirty

Dirty Clean Ferrite

Sleeve

Shielded

Cable

Proximity Switches (except

registration) Photoelectric Cell X 24V dc Relay X Transformer Indicator Lamp X

Data/Communications

XX X

Encoder/Resolver X X Logic circuit power X X

High Speed Registration inputs

PLC Analog I/O X X PLC High Speed Counter input X X

An X in this column indicates a ferrite sleeve fitted to the wire is recommended.

An X in this column indicates a shielded cable is recommended.

Keep unshielded conductors as short as possible and separated from dirty and clean cables as far as possible.

Refer to the section Data/Communications Cables below for more information.

Refer to the chapter High Speed Registration Inputs for more information.

Note: Grounding power cable shields at entry to the cabinet is recommended.

Data/Communications Cables

Data and communication cables that come from a remote structure (refer to the chapter High Frequency (HF) Bonding) will carry noise on their shields. Follow the guidelines listed below when installing data or communication cables.

• Follow the product manual recommendations for termination

resistors, minimum and maximum length, etc.

• Carefully segregate data and communication cables from dirty and

especially very-dirty cables.

• Ground shields to the panel at the point of entry when permitted.

Check your manual for the recommended procedure. Connecting to the 360° shield is preferable to the use of pigtails. If pigtails must be used, they should be kept short. Refer to the section Grounding Cable Shields in Appendix A for more information on grounding cable shields.

• Refer to the chapter Filtering Noise for more information.

Publication GMC-RM001A-EN-P — July 2001

3-8 Segregating Sources and Victims

Minimizing Loops

Wires that form a loop make an efficient antennae. Run feed and return wires together rather than allowing a loop to form. Twisting the pair together further reduces the antennae effects. Refer to the figure below for an illustration.

Note: This applies to potential victim wiring too. Antennae work

equally well in both receive and transmit modes.

Figure 3.4 Avoiding loops in wiring designs

Not Recommended

Routing System Wires and Cables Between Panels

Switch

Good Solution

Better Solution

Switch

Follow the same segregation guidelines when wiring between panels and machine devices.

• Maintain clean, dirty, and very-dirty noise zones.

• Always use separate, grounded, metal wireways.

Publication GMC-RM001A-EN-P — July 2001

Chapter

Shielding Wires, Cables, and Components

Chapter Objectives

Understanding the Shielding Concept

This chapter describes how using shielded cable or steel shields can reduce electrical noise coupling. This chapter covers the following topics:

• Understanding the shielding concept

• Ferrite sleeves

• Mixing categories

You can avoid many of the problems caused by noise by shielding sources and victims (along with their associated wiring) with the use of shielded cable or a supplementary steel shield.

If sources and victims cannot be sufficiently segregated it may be possible to prevent noise coupling by shielding as shown in the figure below.

Figure 4.1 Wire segregation vs. shield

Minimum segregation is

150 mm (6.0 in.) within a panel

Clean Zone

Dirty Zone

Grounded steel shield allows minimal segregation distance.

Publication GMC-RM001A-EN-P — July 2001

4-2 Shielding Wires, Cables, and Components

In the shielding example below the grey plastic wireway (front) is shielded by 0.7 mm (0.03 in.) thick perforated and plated sheet steel. The perforated steel is easy to cut and bend. You can safely route very-dirty wires in the other (black) wireway behind the shield.

Note: By using grey colored wireway for clean zones and black for

dirty and very-dirty zones you will see more clearly when shielding is necessary.

Figure 4.2 Shielding example

Ferrite Sleeves

’

Shielded data cables grounded at both ends (important at high frequencies) may carry noise current due to voltage differences between the two ends. Because the shields have a low impedance, currents may be quite high even though voltage is low. These currents can cause spurious data reception.

By installing ferrite sleeves, the common-mode impedance of the cable is greatly increased at HF thus blocking the noise currents without affecting the signal currents.

In Figure 4.3 the capacitor grounding is very effective and avoids no-grounding rules, but it’s awkward to implement.

Publication GMC-RM001A-EN-P — July 2001

Shielding Wires, Cables, and Components 4-3

Figure 4.3 Ferrite sleeves increase common mode impedance

Ferrite sleeve greatly

increases impedance at RF

Signal

Source

Optional capacitor

Panel A

Differential noise voltage

Figure 4.4 Common mode rejection in shielded cable

Panel B

In this physical circuit, the core and shield are effectively connected together at the transmit end.

Vn is the noise voltage.

In this equivalent circuit, the core and shield form two windings of a 1:1 transformer.

The ferrite sleeve (more turns are better) forms a core increasing the magnetic coupling. The signal is unaffected.

This is known as a common-mode choke.

Tra n sm it

Core

Transmit Shield

Plane

Tra n sm it

Core

Transmit Shield

Plane

1:1

Receive Shield

Receive

Receive Shield

Ferrite Sleeve

Receive

Plane

Core

Secondary voltage matches the primary voltage.

Plane

The following implementation guidelines apply to ferrite sleeves:

• Always install ferrite sleeves to data cables where specified.

• Always use ferrite sleeves when cable length is greater than 10 m

(30 ft).

Core

• If power frequency ground currents are expected, or measured by

current clamp, one shield/ground connection could be made via a 1uF, 50V capacitor.

Publication GMC-RM001A-EN-P — July 2001

4-4 Shielding Wires, Cables, and Components

Ferrite Sleeve Limitations

After implementing all the guidelines presented in this manual, a properly built system should perform well without ferrite sleeves. However, by including sleeves in your installation, the system will avoid problems caused during future modifications.

System installations can benefit from ferrite sleeves, but you should also realize that ferrite sleeves alone are not a substitute for proper noise coupling reduction techniques.

As a rule, include sleeves as standard to obtain the most effective overall system.

For more information about ferrite sleeves, refer to Appendix B.

Mixing Categories

It is often difficult to segregate effectively in a confined space. When strict segregation isn’t practical, minimize overlap and cross cables at right angles. Test results in Appendix A show that even a close parallel run of 0.5 m (20.0 in.) will allow significant noise coupling (refer to the section Wire Segregation Test Results).

You can convert wiring designated dirty or very-dirty to the next lower category by means of shielding using either shielded cable or conduit where required. Figure 4.5 and Figure 4.6 show how this technique may be used to mix categories without breaking the segregation rules.

Publication GMC-RM001A-EN-P — July 2001

EMC

filter to drive

Very-Dirty Zone

Shielding Wires, Cables, and Components 4-5

In Figure 4.5 the cable is locally shielded to cross another zone. Each shield is grounded at each boundary and the cable is run close to the panel. The outer shield A is a thick walled steel conduit.

Figure 4.5 Very-dirty cable in clean zone

Dirty Zone

24V dc I/O

cable

Dirty Zone

Clean Zone

Dirty Zone

Very-Dirty Zone

Motor power

cable

Analog device

cable

Clean Zone

Minimum 150 mm (6.0 in.) segregation

The principle works both ways. In Figure 4.6 the clean cable passes through a very-dirty zone.

Figure 4.6 Clean cable in very-dirty zone

Dirty Zone

24V dc I/O

cable

Dirty Zone

Very-Dirty

Zone

Dirty Zone

Clean Zone

Encoder

cable

Minimum 150 mm (6.0 in.) segregation

Publication GMC-RM001A-EN-P — July 2001

4-6 Shielding Wires, Cables, and Components

Publication GMC-RM001A-EN-P — July 2001

Filtering Noise

Chapter

Chapter Objectives

Understanding the Filtering Concept

This chapter describes how low-pass filters and ferrite sleeves can reduce electrical noise coupling. This chapter covers the following topics:

• Understanding the filtering concept

• Filter performance

• Ultrasonic transducers

• AC line filters

If sources and victims are connected by wiring, you can prevent noise coupling by filtering. Low-pass filters attenuate high frequency noise without affecting the low frequency signals.

Commercial AC Line Filters for Low Voltage Circuits

Provided that motor cable lengths are short, less than 20 m (60 ft), commercial AC line filters work well in low voltage circuits. Two-stage types are preferred.

If motor cable lengths are long, the natural ringing frequency is typically at too low a frequency (below 300k Hz) to be attenuated by commercial AC line filters. To determine if your cables are long, refer to the section Installing Long Motor Cables in Appendix A.

Publication GMC-RM001A-EN-P — July 2001

5-2 Filtering Noise

General Purpose 0-24V ac/dc Filters

The filter diagram shown below forms a classic LC low-pass filter.

Figure 5.1 Filter applied to 24V dc power circuit

Grounded

Common

+24V

Com/Neutral

IMPORTANT

The effectiveness of the LC low-pass filter depends on a perfect bond between the DIN rail and the ground plane panel.

Figure 5.2 Universal 0-24V ac/dc grounded common filter

Clean side

Floating

Common

Segregation

DIN rail

Publication GMC-RM001A-EN-P — July 2001

Capacitor

Ferrite Sleeve

(choke)

Dirty side

Figure 5.3 Floating-Common filter

Filtering Noise 5-3

Clean side

Dirty side

Forming capacitor leads

DIN rail

Capacitors

Ferrite Sleeve

(choke)

The table below lists the part description and part numbers for the filters shown in Figure 5.2 and Figure 5.3.

Part Description RS Components

Part Number

Newark Part Number

Filter Performance

Ground Terminal (1 in, 2 out type) 225-4372 N/A Insulated Terminal (1 in, 2 out type) 426-193 N/A

1 µF, 50V Ceramic Capacitor

Small Ferrite Sleeve

Capacitor value is not critical, but it must be a ceramic type.

The ferrite specification is not critical, but choose a low frequency type if possible.

Alternative ferrite sleeve part numbers: Palomar (FB-102-43) or Schafner (2644665702)

Note: For more information regarding part vendors refer to Appendix B.

211-5558 29F025

239-056

91F6484

The theoretical attenuation of one stage and two stage filters is shown in the table below.

With this filter: Attenuation @ 1M Hz is:

1 stage (2.8k Hz) 55 dB 2 stage (1.2k Hz 110 dB

Publication GMC-RM001A-EN-P — July 2001

5-4 Filtering Noise

Performance Test Set-up

The filter performance test included the following components:

• 24V dc power supply with grounded common filter

• Filter mounted to DIN rail

• Relay coil to simulate an inductive load

• 100M Hz sampling digital storage oscilloscope

• Test components mounted on a large zinc plated steel panel

Figure 5.4 Filter test block diagram

easurement point

1 m (39 in.) wire

Switched load

Filter

Filter under

test

24V dc

PSU

Ground Plane - conductive metal panel

Test Results

This test condition: With

No filter:

No Suppression 200V pk 5.5V pk 674mV pk R/C

5.5V pk 932mV pk 168mV pk Across coil 100R/0.1uF

R/C

2.5V pk 103mV pk 70mV pk Across switch 100R/0.1uF

Transorb

14.9V pk 1.8V pk 658mV pk Across coil

Transorb

8.1V pk 1.4V pk 1.2V pk Across switch

With Capacitor only:

With Capacitor and ferrite sleeve:

Suppression

Publication GMC-RM001A-EN-P — July 2001

Diode 12V pk 63mV pk 63mV pk

Note: Voltages were measured between the measurement point and the ground plane (refer to Figure 5.4 for

exact location.

Filtering Noise 5-5

Ultrasonic Transducers

Xenon Flashing Beacons (strobe lights)

Ultrasonic transducers often induce high noise levels onto their DC supply and signal lines. To reduce noise using ultrasonic transducers:

1. Mount two DC filters close to the device with ferrite sleeves

between the capacitors and the sensor.

2. Feed the DC power supply through one sleeve.

3. Bring out the analog signal via the other sleeve.

Note: Use shielded cable for the analog signal.

The filter ground should be close coupled to the machine metalwork close to the sensor.

Strobe lights can generate high voltage transients on their 24V dc supply lines. To reduce this source of noise, try using one of these two alternatives.

• Mount a DC filter close to the lamp (ferrite sleeve on the lamp

side) with its common attached to chassis ground.

AC Line Filters

• Use shielded cable between lamp and control panel, with DC filter

at the point where the cable leaves the panel.

AC line filters contain capacitors connected between phase and the filter chassis. Line voltage is with respect to ground. The capacitor allows a small but potentially dangerous amount of current to flow to ground.

ATTENTION

To avoid personal injury and/or damage to equipment, ensure AC line filter capacitors are properly connected to safety (PE) ground.

Publication GMC-RM001A-EN-P — July 2001

5-6 Filtering Noise

Figure 5.5 Line filter earth leakage path

Line

Leakage current

Load

Three phase filters are theoretically balanced so the net ground current should be zero. However, a failure of any one capacitor or severe unbalance would cause ground current to flow and trip a circuit breaker.

Earth Leakage/Ground Fault

Earth Leakage Circuit Breakers (ELCB) and Ground Fault Interrupters (GFI) are typical European and US terms for the same device.

The ground/earth current may cause nuisance tripping of Earth Leakage Breakers. Uprated units may help in some cases.

Three phase filters, being balanced, are much less likely to give problems than single phase types.

Publication GMC-RM001A-EN-P — July 2001

Contact Suppression

Chapter

Chapter Objectives

Understanding Contact Suppression for AC Circuits

This chapter describes how contact suppressors for solenoids, relays, and various other switches can reduce electrical noise. This chapter covers the following topics:

• Understanding contact suppression for AC circuits

• Understanding contact suppression for 24V dc circuits

• Contact suppression effects

The one potential noise source that the you can reduce directly is a contact switched load. Even circuits feeding resistive loads will produce significant switching noise. This is because the wiring both upstream and downstream of the contact is inductive. Thus, any switch contact will benefit from suppression.

IMPORTANT

Examples of AC devices requiring contact suppression include:

All switched, inductive loads in the system must be suppressed. This is standard practice in any PLC based control system.

• Contactor controlled motors

• Solenoid coils

• Contactor coils

• Relay coils

• Transformer primaries

• Transformer driven indicator lamps

• Fluorescent cabinet lights (also require line filters close to the

lamp)

• Line filters (often present an inductive load)

The only exception is a load driven by a Zero-Crossing Detector circuit such as Allen Bradley solid-state (Triac) output modules. Zero-crossing switches reduce noise generation virtually to zero. Preferred for frequent operation or close to clean zones.

Publication GMC-RM001A-EN-P — July 2001

6-2 Contact Suppression

Note: Sometimes the supply to a group of zero-crossing Triac outputs

is switched by a mechanical contact for safety purposes. Suppress at the contact in this case.

Methods of AC Contact Suppression

The typical RC suppressor circuit (shown below) consists of a 0.1 µF capacitor in series with a 100 ohm resistor. These components are readily available from many suppliers.

Figure 6.1 RC suppressor circuit

0.1 µF

100 ohms

The typical RC plus transient absorber circuit (shown below) consists of the RC network shown in Figure 6.1 in parallel with a transient absorber. These are used in high current, high energy applications such as motor starters. A three-phase contactor requires three suppressors.

Figure 6.2 RC plus transient absorber circuit

Transient absorber

0.1 µF

100 ohms

Publication GMC-RM001A-EN-P — July 2001

Contact Suppression 6-3

The suppressor across the contact (as shown below, lower) reduces the noise from the wiring inductance as well as the coil inductance.

Figure 6.3 RC suppressor in circuit

Good Solution

Line

Load

Understanding Contact Suppression for 24V dc Circuits

Line

RC suppressor

Better Solution

Load

Examples of DC devices requiring contact suppression include:

• Solenoid coils

• Contactor coils

• Relay coils

Methods of DC Contact Suppression

First choice for DC circuit suppression is a flywheel diode (shown in the figure below), but this does increase the release time which may not be acceptable in all applications. For the transient absorber method, refer to Figure 6.5.

Figure 6.4 Flywheel diode

+24V dc

Common

+24V dc

Common

Good Solution

Flywheel diode

Better Solution

Flywheel diode

Publication GMC-RM001A-EN-P — July 2001

6-4 Contact Suppression

Figure 6.5 Transient absorber

+24V dc

Good Solution

Contact Suppression Effects

Common

+24V dc

Common

Transient absorber

Better Solution

Transient absorber

The waveform below displays 7.2V peaks across the AC terminals of a +24V dc power supply. Noise is due to load on the DC circuit being switched.

Figure 6.6 Unsuppressed inductive load on the DC circuit

10V

7.2V pk

-2

-4

-6

-8

-10V

-10123456789 Source Omron PSU AC Neutral

DC floating, Unsuppressed Relay

µs

Publication GMC-RM001A-EN-P — July 2001

Contact Suppression 6-5

The waveform below displays the effects of an RC suppressor added across the coil on the noise shown in Figure 6.6. Peaks are reduced to

6.4V with significant reduction in duration. Refer to Figure 6.3 (upper) for example of RC suppressor across a coil.

Figure 6.7 Effects of RC suppressor mounted at the load

10V

6.4 mV pk

-2

-4

-6

-8

-10V

-10123456789 Source Omron PSU AC Neutral

DC floating, RC suppressor at Relay coil

(No difference at contact)

µs

The waveform below displays the effects of a flywheel diode across the coil (refer to Figure 6.4, upper). The peak voltage is reduced to

0.9V.

Figure 6.8 Effects of Flywheel Diode at the load

10V

930 mV pk

-2

-4

-6

-8

-10V

-10123456789

Source Omron PSU AC Neutral DC floating, Diode at Relay coil

µs

Publication GMC-RM001A-EN-P — July 2001

6-6 Contact Suppression

The waveform below displays the effects of a flywheel diode across the switch (refer to Figure 6.4, lower). The peak voltage is reduced to

0.3V.

Figure 6.9 Effects of Flywheel Diode at the switch

10V

340 mV pk

-2

-4

-6

-8

-10V

-10123456789 Source Omron PSU AC Neutral

DC floating, Diode at Switch

µs

The small additional noise reduction, when the suppressor is fitted across the switch, is because the wiring between switch and load is also inductive and creates the same inductive spike.

Publication GMC-RM001A-EN-P — July 2001

Power Distribution

Chapter

Chapter Objectives

Understanding Noise in Power Wiring

Three-Phase Power Supplies

This chapter describes bonding, segregating, shielding, and filtering techniques when routing AC and DC power. This chapter covers the following topics:

• Understanding noise in power wiring

• Three-phase power supplies

• Single-phase power supplies

• 24V dc power supplies

AC and DC power wiring usually extends to all parts of a system. Without precautions, noise coupled into any power wiring conductor is distributed throughout the entire system.

To avoid noise related problems caused by three-phase power supplies, observe the following guidelines.

• Treat three-phase wiring as dirty.

• Include line filters for loads that create noise, such as PWM

devices.

Line Filters

Observe the following guidelines when installing line filters.

• Install an individual filter as close as possible to each PWM load

(this is the preferred configuration).

• Install the filter and PWM device on the same panel.

• Treat wiring between filter and drive as very-dirty (provide

shielding as required).

• Segregate input and output wiring as far as possible.

Publication GMC-RM001A-EN-P — July 2001

7-2 Power Distribution

IMPORTANT

The effectiveness of the line filter depends solely on the HF bond between filter case and drive chassis.

Commercial filters are tested, as shown in the figure below, with all devices properly bonded to a conductive metal ground plane. Proper bonding techniques are essential to achieve the published attenuation figures. Refer to the chapter High Frequency (HF) Bonding for more information on bonding.

Figure 7.1 Filter test set-up

Signal

Generator

Filter under test

Ground Plane - conductive metal panel

Measuring Instrument

In the example below, noise couples directly from the filter input wires to the filter output wires and bypasses the filter. You can avoid this common mistake by shielding and/or segregating the cables and reducing the cable length.

Figure 7.2 Improper line filter installation example

AC Line

PWM Drive

ATTENTION

Close spacing

Unshielded cable

Long distance

Line Filter

To avoid personal injury and/or damage to equipment, ensure AC line filter capacitors are properly connected to safety (PE) ground.

Publication GMC-RM001A-EN-P — July 2001

Power Distribution 7-3

Transformers

An isolation transformer is frequently assumed to give good noise isolation. In fact, this only applies if the transformer is equipped with one or more electrostatic (ES) shields, as shown in the figure below.

Figure 7.3 Electrostatically shielded transformer

Primary

Ground Plane

Shield(s) bonded to

ground plane

Secondary

Frame bonded to ground plane

This technique is very effective, though generally EMC filters are required to meet European regulation standards. Observe the following guidelines when installing transformers.

• Install the transformer to the same panel as the rest of your system

(or HF bond from panel-to-panel).

• Treat wiring between transformer and drive as very-dirty (provide

shielding as required).

• Bond shield, if used, with braid directly to the panel. The

transformer mounting bolts are useful for this purpose.

• Segregate input and output wiring as far as possible.

IMPORTANT

The effectiveness of the transformer depends solely on the HF bond between shields and drive chassis.

Publication GMC-RM001A-EN-P — July 2001

7-4 Power Distribution

Single Phase Power Supplies

24V dc Power Supplies

To avoid noise related problems caused by single-phase power supplies, observe the following guidelines:

• Treat single-phase wiring as dirty.

• Include line filters for loads that create noise, such as PWM

devices with DC switch-mode power supplies and fluorescent cabinet lights.

• Include line filters for potentially sensitive loads, such as PLC logic

power.

• Mount the line filter as close to the load as possible.

Switch-mode power supplies do not isolate noise and may generate common-mode noise on both AC and DC lines. Refer to the section Switch-Mode DC Power Supplies in Appendix A for more information.

Linear power supplies normally generate very little noise, but AC line filters or DC output filters are required to attenuate incoming line noise to achieve a clean category.

To avoid noise related problems caused by 24V dc power supplies, observe the following guidelines.

• Connect the common through a ground terminal.

• Decouple the +24V dc line to the same ground terminal with a

1 µ

F, 50V ceramic capacitor to achieve the clean category.

The simplest method for making the ground connection is to use a ground terminal installed on the DIN rail fastened to a zinc plated panel. Refer to Figure 7.4 for an example of the symbol used in diagrams.

Figure 7.4 Ground Plane Symbol

This symbol indicates direct connection to a ground plane.

Publication GMC-RM001A-EN-P — July 2001

Power Distribution 7-5

24V dc Distribution

Route power wiring according to clean/dirty zones. Segregate the following load classifications:

• Clean loads that are potentially sensitive to noise and which do

not create significant noise, e.g. controller logic supplies.

• Dirty loads that are insensitive to noise but may emit moderate

levels of noise, e.g. relay circuits.

Note: Refer to the chapter Segregating Sources and Victims for a

detailed listing of categories.

Note: Refer to the chapter High Speed Registration Inputs for special

treatments of registration input devices.

24V dc PSU Zoning Methods

The following two methods of 24V dc power supply zoning are described in this chapter.

• Single 24 volt power supply with filtering between zones.

• Dual 24 volt power supplies.

Publication GMC-RM001A-EN-P — July 2001

7-6 Power Distribution

Single 24V dc Switch-Mode PSU Zoning Example

In the figure below, a 24V dc supply is mounted in the dirty zone, because it may create noise. But, the noise is reduced by filtering before the output enters the clean zone.

Figure 7.5 24V dc power distribution with single PSU

24V com

Dirty Load

Clean Load

+24V

24V dc PSU

Filter

Dirty Zone

Segregation

Clean Zone

Filter

De-coupling

capacitor

Grounded, de-coupling capacitors are used at each clean load (refer to the chapter High Frequency (HF) Bonding for details). Provided the system is correctly bonded, the multiple common/ground connections are not a problem. The copper becomes a backup conductor. No segregation or filtering is necessary for the load in the dirty zone.

Publication GMC-RM001A-EN-P — July 2001

Power Distribution 7-7

In the figure below, a filter is pictured between the clean zone (grey wireway) and the dirty zone (black wireway). Refer to the chapter Filtering Noise for details regarding filters.

Figure 7.6 Filter between zones

Publication GMC-RM001A-EN-P — July 2001

7-8 Power Distribution

Dual Switch-Mode 24V dc PSU Example

In the figure below, dirty and clean zone loads have dedicated power supplies. Segregation and filtering are used (as in Figure 7.5) to reduce the noise in the power supply for clean zone needs.

Figure 7.7 24V dc power distribution with dual PSU

24V com

Dirty Load

Clean Load

24V com

Dirty Zone

Clean Zone

Filter

+24V

24V dc PSU

Segregation

Filter

De-coupling

capacitor

+24V

Note: Clean PSU is mounted in the dirty zone because it typically

generates noise in the switching process.

Publication GMC-RM001A-EN-P — July 2001

Power Distribution 7-9

Linear PSU

The linear PSU does not generate noise on its AC terminals, as does a switch-mode supply, however, some noise reduction provisions are still recommended.

Linear PSU Mounted in Clean Zone

In the figure below, the linear power supply is mounted in the clean zone, but the AC line feeding it requires filtering. The AC line filter is positioned between zones and attenuates line noise which may otherwise be passed through to the DC circuit.

Figure 7.8 Linear PSU mounted in Clean Zone

Dirty Zone

Filter

24V dc Linear PSU

De-coupling

capacitor

+24V

Segregation

Clean Zone

Clean Load

24V com

Publication GMC-RM001A-EN-P — July 2001

7-10 Power Distribution

Linear PSU Mounted in Dirty Zone

In the figure below no AC line filter is required because the linear PSU does not generate noise and the AC line noise is filtered by the DC filter.

Figure 7.9 PSU mounted in Dirty Zone

Dirty Zone

Clean Zone

24V dc

Linear PSU

Segregation

Filter

De-coupling

capacitor

+24V

Clean Load

24V com

Publication GMC-RM001A-EN-P — July 2001

Power Distribution 7-11

Special Applications for 24V dc PSUs

This section contains information considered application specific and does not apply to all installations.

Floating Requirement

If it is necessary to maintain a floating common, a modified filter may be used to ground the common at HF frequencies only. Refer to the chapter Filtering Noise for details regarding filters.

Figure 7.10 Floating Common

Dirty Zone

Clean Zone

24V dc PSU

Filter

Segregation

Filter

De-coupling

capacitor

+24V

24V com

Dirty Load

Clean Load

Publication GMC-RM001A-EN-P — July 2001

7-12 Power Distribution

Segregation and Filtering Variations

Once the principles of segregation and filtering are understood it is possible to vary the strategy to suit special requirements.

For example, the clean zone does not have to be a single entity. As shown in the figure below, you can create separate local clean zones. Refer to the chapter Segregating Sources and Victims for guidelines on crossing zones.

Figure 7.11 Separate Clean Zones

+24V

24V com

Dirty Zone

Filter

Clean Zone

Segregation

Filter

Clean Zone

Publication GMC-RM001A-EN-P — July 2001

Power Distribution 7-13

Long Power Cable Runs

The 24V dc lines entering or leaving panels that cannot be bonded together by flat strips (no longer than 10 times the width) should have filters at the point of entry.

Figure 7.12 Long cable runs between panels

Panel A

+24V

24V com

Panel B

Note: If heavy circulating currents at power frequency are likely, the

floating filter technique or separate, local PSU’s, may be safer to use.

Publication GMC-RM001A-EN-P — July 2001

7-14 Power Distribution

Publication GMC-RM001A-EN-P — July 2001

Motor Wiring

Chapter

Chapter Objectives

Understanding Noise in Motor Power Wiring

This chapter describes shielding, grounding, and splicing techniques for use with motor wiring. This chapter covers the following topics:

• Understanding noise in motor power wiring

• Shielding motor power cables

• Grounding motor power cable shields

• Applying ferrite sleeves

• Splicing motor power cables

• Handling excess cable

• Installing long motor cables

The PWM Drive to motor power conductors are typically the most intense noise source in a system. Proper implementation of shielding, grounding, splicing, and treatment of excess cable is essential to reducing noise in your system. In the figure below:

• The unshielded conductors radiate an electric noise field that

couples capacitively with adjacent wiring.

• Stray capacitance at A & C cause ground currents to flow creating

a magnetic noise field that couples inductively with adjacent wiring.

Figure 8.1 Motor power cable noise

Drive

Heatsink

(connected

to chassis)

Panel

DC+

DC-

Radiation by E (electric) field

Unshielded motor cable

both conducts and

radiates noise

Publication GMC-RM001A-EN-P — July 2001

Windings

Radiation by

H (magnetic)

field from this

Machine Structure

Motor

loop

8-2 Motor Wiring

Shielding Motor Power Cables

The benefits of using shielded cable are listed below (also refer to Figure 8.2).

• The shield strongly attenuates the electric field (E field) noise.

• Core to shield capacitance is added to the stray capacitance at A &

C increasing ground currents in the loop A, C, D, E, and F.

• These currents generate a magnetic field (H field).

It is important to minimize the area of this loop as far as possible by routing the cable close to grounded metalwork.

Figure 8.2 Shielded motor power cable

Drive Motor

Heatsink

(connected to

chassis)

DC+

Cable shield

introduces more stray

capacitance to ground

Windings

Grounding Motor Power Cable Shields

Cable shield

grounded both

ends

Panel

DC-

Machine Structure

Observe the following guidelines when bonding the motor power cable shield to ground. Bond motor power cable shields:

• At the motor frame.

• To the panel at entry to the cabinet (optional).

• To the drive (amplifier) chassis. If a connection point is not

provided, bond to the adjacent panel.

These connections must be made at the circular section, not by creating pigtails. Refer to the section Grounding Cable Shields in Appendix A for examples of grounding at the circular section.

Publication GMC-RM001A-EN-P — July 2001

Motor Wiring 8-3

Applying Ferrite Sleeves

Splicing Motor Power Cables

A ferrite sleeve around the three power conductors as they leave the drive will help to reduce common-mode noise current. Take all three conductors two or three times through the core. If it runs hot reduce the number of turns.

Note: Not all drives allow the use of a ferrite sleeve around power

conductors. Refer to your manual for specific applications.

Avoid splicing motor power cables when ever possible. Ideally, motor power cables should run continuous between the drive and motor terminals. The most common reason for splicing is to incorporate high-flex cable for continuous flexing applications.

If necessary, the preferred method of splicing is to use a fully shielded bulkhead connector. Splicing can also be accomplished using a grounded and shielded junction box, as shown in the figure below.

Figure 8.3 Spliced cable using junction box

Observe the following guidelines when installing a junction box:

• Shield drain wire must be spliced only to mating shield drain

wires and not grounded at the junction box.

• Feedback shields must be passed through pin for pin.

• Separate junction boxes for power and feedback are required.

Publication GMC-RM001A-EN-P — July 2001

8-4 Motor Wiring

Handling Excess Cable

Observe the following guidelines when handling excess cable:

• Do not coil excess cable of different types (i.e. motor power and

feedback) together. An efficient transformer is formed at HF.

• Cable lengths should ideally be trimmed to fit the application.

• If excess cable cannot be trimmed, it should be laid in an 'S' or

figure eight pattern (refer to the figure below).

Figure 8.4 Excess cable treatment

Preferred Methods

Poor Method

Installing Long Motor Cables

Motor cables are defined as long when the motor frame is not bonded close enough to the drive panel to be considered a single ground plane. To be considered a single ground plane, the parts must be connected by a surface which is no longer than ten times its width. Refer to the chapter High Frequency (HF) Bonding for methods of achieving a single ground plane.

Observe the following guidelines when installing long motor cables:

• Bonding should be by the widest practical means. Wide cable tray

is effective when it is made of zinc plated steel and carefully bonded at the ends to control panel and motor frame.

• Zinc plated sheet steel channel is also effective. The fact that the

width is folded into a U shape does not matter. A closing lid helps.

• Solid steel conduit bonded at both ends is effective.

• The spiral construction of flexible conduit makes it less attractive

for RF shielding because the spiral shape forms an inductor, even with partially shorted turns.

Publication GMC-RM001A-EN-P — July 2001

High Speed Registration Inputs

Chapter

Chapter Objectives

Understanding Registration Inputs

This chapter describes how wiring, sensitive to electrical noise, benefits from proper noise reduction strategies. This chapter covers the following topics:

• Understanding registration inputs

• Noise reduction methods

• Power supply wiring options

• Signal noise filter options

• Registration error

High speed registration inputs are potentially sensitive to noise by design. Typically, the specification states that the input responds within 1 microsecond of the signal going high, while in practice, the response is often even faster. Noise pulses of this duration are common in a typical drive system.

IMPORTANT

Coupling is usually capacitive if unshielded cable is run near noisy cables or if voltage differentials exist between the detector mounting and the equipment carrying the registration input. For these reasons, treat high speed registration input circuits with special care.

Publication GMC-RM001A-EN-P — July 2001

9-2 High Speed Registration Inputs

Noise Reduction Methods

This section provides installation guidelines for reducing noise coupling into high speed registration inputs.

Wiring

Follow these guidelines to reduce noise coupling in wiring:

• Always use shielded cable.

• Connect shields at both ends and at the circular section.

• Always run the cable in a clean zone.

• Segregate the cable as far as practical from dirty and (especially)

very-dirty wiring.

• Always make cable runs as short as possible.

Power

Follow these guidelines to reduce noise coupling in power supplies:

• The power supply should be as clean as possible.

• Use a filter if a switch-mode supply is used (refer to the chapter

Filtering Noise for more information).

• Obtain +24V dc power from a clean supply and provide a filter

(refer to the chapter Filtering Noise for more information).

• Always ground the common.

Shared Power Supply

Observe the following guidelines when sharing power between the registration input and other clean loads. Refer to Figure 9.1 for a shared power wiring diagram.

• Provide a filter just prior to the registration input, even if the +24V

dc supply has a clean rating.

• Mount the filter on a separate DIN rail, especially if a painted

panel is used.

Publication GMC-RM001A-EN-P — July 2001

Figure 9.1 Shared registration power supply

High Speed Registration Inputs 9-3

Dirty Zone

Segregation

Clean Zone

Insulated mounting (preferred)

Detector

com

+24V

+24V com

Clean Load

Registration Input

In figure below a pigtail shield connection is used for the short cable run to the input and a clamp connection for the long run from the sensor. Refer to Appendix A for more information on grounding cable shields.

Figure 9.2 Registration power filter

From sensor

24V dc supply

To registration input

Publication GMC-RM001A-EN-P — July 2001

9-4 High Speed Registration Inputs

Dedicated Power Supply

In the figure below, the registration input has a dedicated linear power supply.

Figure 9.3 Dedicated registration power supply

Dirty Zone

Filter

24V dc Linear PSU

Insulated mounting (preferred)

Detector

com

Segregation

Clean Zone

Keep short or shield (ground shield on both ends)

Registration Input

Detection Device Mounting

A line driver or push-pull output is preferred, but not widely available except in specialized photoelectric sensors for mark detection.

Publication GMC-RM001A-EN-P — July 2001

Ideally, the device body should be insulated from the machine structure and connected to the cable shield.

If the sensor cannot be insulated, ground the shield to the structure or sensor mounting.

High Speed Registration Inputs 9-5

Proximity Switches

Proximity switches are especially vulnerable in the off state since the signal line is disconnected at the switch, forming an efficient antenna. Observe the following guidelines when using proximity switches:

• Insulate the mounting, if possible, and connect the body to the

cable shield.

• Arrange to be normally on (i.e. hole-operated instead of

target-operated).

• Register on the falling edge. With the line effectively disconnected

(off condition) stray capacitance causes the signal voltage to fall slowly. Even low levels of noise may then cause false triggering of inputs without hysteresis.

• When the proximity switch is supplied with unshielded cable,

keep the unshielded length to a minimum by joining to shielded cable inside a shielded terminal box mounted close to the switch. Bond the terminal box to the sensor body.

Signal Noise Filter Options

Most registration inputs have a response time of 1 microsecond or less. In practice, such speed is rarely required. A simple, low-pass filter will slow the response time but will increase the noise immunity. Observe the following guidelines for best results in all configurations.

• Keep the length of cable between filter and control to a minimum.

• Bond the filter common securely to the controller chassis.

Publication GMC-RM001A-EN-P — July 2001

9-6 High Speed Registration Inputs

Single Voltage Input (24V or 5V)

The figure below illustrates a typical registration filter circuit.

Figure 9.4 Registration filter circuit

• R1 lowers the circuit impedance which improves noise immunity.

It also ensures that the signal voltage falls rapidly when the detector turns off. A lower R value is better, but is limited by the drive capability of the detector and the dissipation in the resistor. A 470 ohm resistor will dissipate 1.2W at 24V dc if on continuously, hence it should be rated at 2W.

• The maximum value of R2 depends on the impedance of the

registration input (a volt drop to 10% of nominal is ideal). If input impedance is less than 4.7k ohms, then R2 will require a lower value (i.e., 10% of input impedance). If R2 is changed, use this

formula for the on-delay: Delay (uS) = R2 (ohm) x C (

F). A value

of 470 ohms should be acceptable for most cases.

• Capacitor C, together with R2, determines the on-delay. Capacitor

C, together with R1 + R2, determines the off-delay (as shown in the table below).

Publication GMC-RM001A-EN-P — July 2001

k ohm

0.47 0.47 4.7 2 4 14 23

0.47 0.47 10 5 9 30 29

0.47 0.47 22 10 21 65 36

0.47 0.47 47 22 44 139 43

0.47 0.47 100 47 94 295 49

0.47 0.47 220 100 207 649 56

k ohm

Delay On

µs

Delay Off

µs

Noise Attenuation factor

@ 1MHz

Noise Attenuation

@1MHz dB

High Speed Registration Inputs 9-7

Dual Voltage Inputs (24V or 5V)

Where the input is split into 5V and 24V, with inputs sharing the same common, it is important that the 5V input is not left floating. In the figure below, the 24V and 5V inputs are shorted together and fed at 5V.

Figure 9.5 Registration filter circuit (24V/5V)

+24V

From Detector

Common

+24V

+5V

To Registration Inputs

Common

The on-delay and off-delay times are shown in the table below.

k ohmR2k ohm

0.100 0.390 220 22 2 14 23

0.100 0.390 220 22 5 30 29

0.100 0.390 220 22 10 65 36

0.100 0.390 220 22 22 139 43

0.100 0.390 470 47 47 295 49

Delay On

µs

Delay Off

µs

Noise Attenuation factor

@ 1MHz

Noise Attenuation

@1MHz dB

0.100 0.390 1000 100 100 649 56

Publication GMC-RM001A-EN-P — July 2001

9-8 High Speed Registration Inputs

Registration Error

The following charts help to estimate the error due to time delays. The detector delay may be much greater than the filter delay, so it is important to add the two together.

Figure 9.6 Registration Error vs. Delay (metric units)

0.1

Error mm

0.01

0.001

0.0001 10 20 50 100 200 500 1000

Li near V elocit y m/ min

1 uS 2 uS 5 uS 10 uS 20 uS 50 uS 100 uS

Figure 9.7 Registration Error vs. Delay (British units)

0.1

0.01

0.001

Error ins

0.0001

0.00001

0.000001 20 50 100 200 500 1000 2000

Linear Velocity ft/min

Publication GMC-RM001A-EN-P — July 2001

1 uS 2 uS 5 uS 10 uS 20 uS 50 uS 100 uS

Figure 9.8

Registration Error vs. Delay (rotary units)

0.1

Error de

0.01

0.001

0.0001 20 50 100 200 500 1000 2000

High Speed Registration Inputs 9-9

Velocity RPM

1 uS 2 uS 5 uS 10 uS 20 uS 50 uS 100 uS

Error Compensation

If the registration signal delay is constant, it will have the effect of applying a position error proportional to velocity. In this case it may be possible to apply a software correction.

Software Solutions

It is possible to increase noise resistance with your software, especially if the problem is false triggering on the falling edge (which is usually much slower than the rising edge).

Try one of the following techniques before re-arming or looking for the next registration event.

• Add wait-for-registration-input-low.

• Add a timer after a registration event (to allow the switch signal to

go low).

• Add wait-for-position-greater-than-x (to allow the switch signal to

go low).

Publication GMC-RM001A-EN-P — July 2001

9-10 High Speed Registration Inputs

Publication GMC-RM001A-EN-P — July 2001

Encoders

Chapter

Chapter Objectives

Understanding Encoders

This chapter describes bonding, segregating, shielding, and filtering techniques for use with encoders. This chapter covers the following topics:

• Understanding encoders

• Noise reduction methods

• Power supply wiring options

Encoder input circuits are, by their nature, potentially sensitive to noise. The signal is typically a square wave of about 500kHz at maximum speed. In order to preserve a reasonable square pulse, the circuit must handle at least ten times higher frequencies. Unfortunately, a response of 5MHz is ideally suited to detecting the noise spikes in a drive system.

The internal encoder circuitry should be relatively immune if it is well designed but there is often a long cable run to the control input circuitry. Coupling is usually due to voltage differentials between the encoder mounting and the drive input.

Noise Reduction Methods

This section provides installation guidelines for reducing noise sources near encoder input circuits.

Driver Type

IMPORTANT

Driver type is generally dictated by the drive product but A quad B, differential, or line driver outputs are preferred.

Publication GMC-RM001A-EN-P — July 2001

10-2 Encoders

Wiring

• Always use shielded cable (manufacturers usually specify

appropriate cable).

• Segregate the cable as far as practical from dirty and especially

very-dirty wiring.

Power

• Always use the internal power supply when available.

• Ensure the power supply has a clean rating (refer to Figure 10.1

and Figure 10.2 for linear and switch-mode power supply examples).

• Use a filter if a switch-mode supply is used (refer to the chapter

Filtering Noise for more information).

• Always ground the common.

Mounting

• Insulate the encoder body from the machine structure and connect

it to the cable shield.

Note: This strategy also requires an insulated shaft coupling.

• If the encoder cannot be insulated, connect the cable shield to

ground at the encoder case and drive chassis (or dedicated termination).

Publication GMC-RM001A-EN-P — July 2001

Encoders 10-3

Power Supply Wiring Options

This section provides filtering options of power supply configurations for your encoder. For more information regarding filters, refer to the chapter Filtering Noise.

Figure 10.1 Linear power supply example

Dirty Zone

Filter

5/12V dc Linear PSU

Insulated mounting and coupling preferred

Encoder

com

Segregation

Clean Zone

Keep short or shield (ground shield on both ends)

Encoder Input

Figure 10.2 Switch-mode power supply example

Filter

Dirty Zone

Clean Zone

Insulated mounting and coupling preferred

Encoder

5/12V dc PSU

Segregation

com

Keep short or shield

Encoder Input

Publication GMC-RM001A-EN-P — July 2001

10-4 Encoders

Publication GMC-RM001A-EN-P — July 2001

Chapter

Measuring Noise Reduction Effectiveness

Chapter Objectives

Understanding Noise Measurement

Methods for Measuring Noise

This chapter describes the equipment, methods, and various guidelines for measuring noise reduction effectiveness. This chapter covers the following topics:

• Understanding noise measurement

• Methods for measuring noise

• Measuring noise

• General guidelines for measuring noise

The ability to measure the effectiveness of noise reduction efforts and to determine if a system is within tolerance is important. However, it can be very difficult to obtain meaningful and repeatable results.

European EMC regulations are based on spectrum analysis (displaying amplitude vs. frequency). An RF spectrum analyzer is an expensive specialist tool, but necessary for pre-compliance testing if this is the requirement. Usually, a specialist EMC testing company is hired to perform such tests and the subject is beyond the scope of this document.

For troubleshooting drive systems, an oscilloscope (displaying amplitude vs. time) is more practical. You can determine the effectiveness of your noise reduction efforts by measuring the amplitude of the largest noise spikes at various points in the system.

There are three primary methods of measuring noise:

• E-field sniffing (electric field)

• H-field sniffing (magnetic field)

• Direct voltage measurements

The first two methods (E-field and H-field sniffing) are best used to quickly check for intense noise sources, however direct voltage measurements along the system wiring is the most reliable indicator of noise performance. Conducted noise (via capacitance and system wiring) is the most common cause of functional problems.

Publication GMC-RM001A-EN-P — July 2001

11-2 Measuring Noise Reduction Effectiveness

Professional probes are available in each category and would be mandatory for testing to EMC regulations but simple methods are sufficient for this purpose and are described below (refer to Appendix B for EMC suppliers).

Measuring Noise

This section describes the tools and methods used to measure noise.

Oscilloscope Specifications

When measuring noise, choose an oscilloscope with the following features:

• Digital storage

• At least 100 MHz sampling rate

• Trigger that is easily set to a known voltage

• Standard voltage probes

• Differential-mode function (differential voltage probe is a good

alternative, but an additional cost)

• Probe bandwidth of at least 20 MHz.

• Battery power (optional)

Publication GMC-RM001A-EN-P — July 2001

Oscilloscope Settings for Measuring Noise Peaks

Measuring noise peaks is often difficult since PWM induced peaks are short and typically vary in amplitude widely with time.

To set up your system and oscilloscope for measuring noise peaks:

1. Set the timebase to 1 microsecond per division.

2. Set the trigger so that peaks are captured.

3. Gradually increase the trigger level until triggering just stops.

4. Measure the maximum peak voltage displayed.

Measuring Noise Reduction Effectiveness 11-3

E-Field Sniffing Method

The E-field is the electric field capacitively coupled to the probe. To use the E-field sniffing method:

1. Attach a 150 mm (6 in.) length of stiff insulated wire to the probe

tip to form an antenna.

2. Remove the probe ground clip or attach it to the scope cable to

ensure it does not contact anything.

3. Hold the wire parallel to and touching potential victim wiring and

measure the voltage spikes.

Note: The signal observed is with respect to the scope ground. Check

the method by holding the wire against the panel. There should be little noise observed (refer to the section Ground Loops for more information).

Figure 11.1 Simple E-field probe

Publication GMC-RM001A-EN-P — July 2001

11-4 Measuring Noise Reduction Effectiveness

H-Field Sniffing Method

The H-field is the magnetic field inductively coupled to the probe. Connect the scope probe ground clip to the probe tip forming a small loop. Hold the loop close to potential victim wiring. The loop antenna is sensitive to orientation, so test all three axes to determine the maximum reading at each location.

Figure 11.2 Simple H-field probe

Publication GMC-RM001A-EN-P — July 2001

Direct Voltage Measurement Method

Direct voltage measurement methods exist for both AC and DC circuits. Each category are described in the paragraphs below.

Measuring DC Circuits

Direct voltage measurements with respect to a known good ground are made at chosen points in your DC circuit using a standard 1x scope probe. Set signal coupling to AC.

Measuring Noise Reduction Effectiveness 11-5

Measuring AC Circuits

Line voltage AC circuits are more difficult to measure since 50/60Hz AC waveforms will swamp the noise signals if a standard 10x or 100x scope probe is used.

Professional noise probes include a 150kHz high-pass filter to attenuate power frequency signals, but such a filter is easily built (refer to Figure 11.3).

Figure 11.3 High-pass filter circuit, 150kHz, 1 pole

Shielded enclosure

BNC socket from probe

ATTENTION

1000 pF

2 kV

1000 Ω

0.25 W

To avoid personal injury or damage to equipment, the capacitor must be rated at 2 kV or higher.

BNC plug to scope

With this filter installed between a 1x scope lead and the scope input, AC lines may be examined for noise. The 50/60 Hz waveform will be reduced to around 200 mV peak.

Note: Note that a 10x probe will attenuate far more than 10x in this

situation and should not be used.

Publication GMC-RM001A-EN-P — July 2001

11-6 Measuring Noise Reduction Effectiveness

For BNC cases (as shown in Figure 11.4) refer to the following list of suppliers:

• Pomona Electronics, Part # 3752

• RS Components, Part # 189-0258

For more information on these and other suppliers, refer to Appendix B.

Figure 11.4 High-pass filter construction, 150 kHz, 1 pole (signal flow is left to right)

ATTENTION

To avoid personal injury or damage to equipment, always connect the probe ground clip to reference ground. Connecting the ground clip to line voltage may cause the scope chassis and controls to reach potentially lethal line voltage.

Grounding Your Probe (reference ground)

If the panel is plated and everything is bonded to it then the nearest point on the panel is the best reference ground point. With proper bonding the whole panel is a ground plane and the ideal reference. With a painted panel it is almost impossible to define a good ground because all the components are at different RF potentials. However, because a properly bonded panel (even one that’s painted) maintains the same electrical potential at all points, it is still the best reference ground.

Publication GMC-RM001A-EN-P — July 2001

Measuring Noise Reduction Effectiveness 11-7

Ground Loops

A line-powered oscilloscope may introduce noise via the ground loop formed by the separate line supply and the connection of the probe to system ground. Methods to reduce this type of noise are listed below.

• Connect a braided strap between the scope chassis and the panel.

Most scopes have a ground terminal provided for this purpose.

• Pass the scope lead through a ferrite sleeve several times.

• Use a battery powered scope and place it inside the control

cabinet close to the panel.

• Use a scope with differential inputs. Refer to the section

Differential Measurements for more information.

• Extend the scope probe lead. Refer to Figure 11.6 for an

illustration.

Differential Measurements

Differential measurements eliminate ground loops and allow the scope to be grounded to its own supply ground. Two methods to reduce this type of noise are given below.

Differential Voltage Probes

Differential voltage probes, as shown in Figure 11.5, use only one scope input. Since they cancel common-mode voltage between the measured circuit and the scope common, ground loop problems are greatly reduced.

The main limitation is that of limited common-mode rejection. To avoid saturating the amplifier when measuring noise at line voltage the attenuation must be set to 1/100 or 1/200. This way the noise signal of interest is attenuated by the same amount. Increasing the scope sensitivity to compensate amplifies any internal probe or scope noise. Tips for using differential scope probes are listed below.

• Connect both probe tips to the same point in the circuit under test.

No signal should be seen if the differential function is working correctly. Refer to the section Checking Your Method for Effectiveness for details. For best results, use the method as described.

Publication GMC-RM001A-EN-P — July 2001

11-8 Measuring Noise Reduction Effectiveness

• Use a high-pass filter between the probe and the scope input

when checking AC circuits. Refer to Figure 11.4 for filter construction details.

Note: Before installing the high-pass filter, check that the signal

Figure 11.5 Typical differential voltage probe

does not overload the voltage probe at the chosen division ratio.

Publication GMC-RM001A-EN-P — July 2001

Differential Scope Inputs

Refer to these guidelines using an oscilloscope with two inputs in differential mode.

• The trigger must also operate in differential mode. Check your

user manual for compatibility and instructions.

• Use two matched high-pass filters (one for each probe) for AC line

checks as described above. Refer to Figure 11.4 for filter construction details.

• Connect both probe tips to the same point in the circuit under test.

The residual noise signal should be much smaller than the measured value if the differential function is working. Refer to the section Checking Your Method for Effectiveness for details.

• Avoid forming large loops with your probes by twisting the two

leads together as far as possible.

Measuring Noise Reduction Effectiveness 11-9

Scope Probe Lead Extension

Refer to these guidelines, and the figure below, when extending the scope probe.

• Keep the extension cable as short as possible.

• Make several turns through the ferrite sleeve.

• Only use 1x probes (10x probes will attenuate HF signals by more

than ten times).

Figure 11.6 Extending the scope lead

Scope

BNC / BNC

extension

cable

BNC bulkhead

socket

Ferrite sleeve

Component mounting panel

1x Scope probe

Checking Your Method for Effectiveness

Connect the probe ground clip to the chosen ground reference and then connect the probe to the same point. It would be reasonable to expect zero signal, but it is common to see significant levels of noise. The main sources of such noise are given below.

• Poor ground reference. Refer to the section Grounding Your Probe

(reference ground) for guidelines.

• Scope power supply introducing noise. Refer to the section

Ground Loops for guidelines.

• Local magnetic noise field. Refer to the section H-Field Sniffing

Method for details.

Note: It can be seen from this why extending the scope probe

ground wire is not recommended.

Without constant checking, it difficult to know when the observed noise waveform is real or a measurement artifact.

Publication GMC-RM001A-EN-P — July 2001

11-10 Measuring Noise Reduction Effectiveness

Identifying the Noise Source

Two methods for identifying the source of a noise spike are listed below.

• Disable each potential source in turn until the spike disappears.

• Correlate the noise signal with PWM sources by displaying the

PWM waveform on a second channel. If the PWM source is the culprit, the noise signal will remain synchronized to the edges of the PWM waveform. Use a differential probe (phase to phase) or high-pass filter (phase to ground), connected to the suspect drive terminals, to display the PWM edges.

Intermittent Noise

If noise from mechanical contacts (e.g., a motor contactor) is suspected, the technique is a little different. Because of the variable nature of the peak amplitude, the best method is to operate the suspect device (for example) ten times in quick succession by overriding the control system. If this is not practical, monitor the device long enough to observe a number of operations. Progressively increase the trigger level as before.

General Guidelines for Measuring Noise

This section contains general guidelines for measuring noise. Tips on understanding acceptable noise levels, noise measurement methods that don’t work, and system monitoring methods are discussed.

What are Acceptable Noise Levels?

No national or international standards for instantaneous peak voltage levels are known, but a very conservative approach would be to assume that a TTL gate may be closely coupled to a nominally clean circuit. Then, the noise immunity of a TTL gate (around 1.0V) becomes the critical level. This implies an allowable maximum of (for example) 500mV to allow for some margin of safety.

Publication GMC-RM001A-EN-P — July 2001

Rockwell Automation System Design User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Important User Information

Table of Contents

Preface

Who Should Use this Manual

Purpose of this Manual

Contents of this Manual

Related Documentation

Conventions Used in this Manual

Chapter Objectives

What is Electrical Noise?

• Understanding the need for electrical noise control

CE Compliance

Best Practices

Noise Control Basics

Noise Sources

Noise Victims

Coupling Mechanisms

Conducted Noise

Capacitance

Mutual Inductance

Electromagnetic Radiation

Solutions for Reducing Noise

Implementation

Measuring Effectiveness

Chapter Objectives

Understanding the Source of Electrical Noise

Noise Example 1

Noise Example 2

The Ground Plane Principle

Extending the Ground Plane Principle

Grounding a PCB to the Drive Chassis

Noise Solutions Using the Ground Plane Principle

Grounding to the Component Mounting Panel

Doors

Adjacent Panels

Grid and Raised Floor

Mezzanine Floor

Machine Structure

New Buildings

Existing Buildings

Limits

Grounding (Safety Earth)

Chapter Objectives

Understanding the Segregation Concept

Noise Zones

Ensuring CE Compliance at Build Time

Zone Classification

Component Categories

Routing Wires and Cables Within a Panel

Wire and Cable Categories

Routing System Wires and Cables Between Panels

Chapter Objectives

Understanding the Shielding Concept

Ferrite Sleeves

Ferrite Sleeve Limitations

Mixing Categories

Chapter Objectives

Understanding the Filtering Concept

Commercial AC Line Filters for Low Voltage Circuits

General Purpose 0-24V ac/dc Filters

Filter Performance

Performance Test Set-up

Test Results

Ultrasonic Transducers

Xenon Flashing Beacons (strobe lights)

AC Line Filters

Earth Leakage/Ground Fault

Chapter Objectives

Understanding Contact Suppression for AC Circuits

Methods of AC Contact Suppression

Understanding Contact Suppression for 24V dc Circuits

Methods of DC Contact Suppression

Contact Suppression Effects

Chapter Objectives

Understanding Noise in Power Wiring

Three-Phase Power Supplies