System Design for Control of Electrical Noise
Reference Manual
Important User Information |
Because of the variety of uses for the products described in this |
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publication, those responsible for the application and use of this |
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control equipment must satisfy themselves that all necessary steps |
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have been taken to assure that each application and use meets all |
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performance and safety requirements, including any applicable laws, |
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regulations, codes and standards. |
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The illustrations, charts, sample programs and layout examples |
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shown in this guide are intended solely for purposes of example. |
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Since there are many variables and requirements associated with any |
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particular installation, Allen-Bradley does not assume responsibility |
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or liability (to include intellectual property liability) for actual use |
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based upon the examples shown in this publication. |
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Allen-Bradley publication SGI-1.1, Safety Guidelines for the |
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Application, Installation and Maintenance of Solid-State Control |
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(available from your local Allen-Bradley office), describes some |
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important differences between solid-state equipment and |
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electromechanical devices that should be taken into consideration |
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when applying products such as those described in this publication. |
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Reproduction of the contents of this copyrighted publication, in |
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whole or part, without written permission of Rockwell Automation, |
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is prohibited. |
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Throughout this manual we use notes to make you aware of safety |
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considerations: |
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Identifies information about practices or |
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ATTENTION |
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circumstances that can lead to personal injury or |
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! |
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death, property damage or economic loss. |
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Attention statements help you to:
•identify a hazard
•avoid a hazard
•recognize the consequences
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Identifies information that is critical for successful |
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IMPORTANT |
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application and understanding of the product. |
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Allen-Bradley is a registered trademark of Rockwell Automation.
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Table of Contents |
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Preface |
Who Should Use this Manual . . . . . . . . . . . . . . . . . . . . . . . |
P-1 |
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Purpose of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . |
P-1 |
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Contents of this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . |
P-2 |
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Related Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . |
P-3 |
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Conventions Used in this Manual . . . . . . . . . . . . . . . . . . . . |
P-3 |
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Chapter 1 |
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Electrical Noise Control Overview |
Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-1 |
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What is Electrical Noise?. . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-1 |
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Understanding the Need for Electrical Noise Control . . . . . . |
1-1 |
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CE Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-1 |
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Best Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-2 |
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Noise Control Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-2 |
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Noise Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-2 |
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Noise Victims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-4 |
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Coupling Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-4 |
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Conducted Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-4 |
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Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-5 |
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Mutual Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-5 |
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Electromagnetic Radiation . . . . . . . . . . . . . . . . . . . . . . . |
1-6 |
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Solutions for Reducing Noise . . . . . . . . . . . . . . . . . . . . . . . |
1-6 |
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Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-7 |
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Measuring Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . |
1-7 |
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Chapter 2 |
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High Frequency (HF) Bonding |
Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-1 |
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Understanding the Source of Electrical Noise . . . . . . . . . . . |
2-1 |
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Noise Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-2 |
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Noise Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-3 |
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The Ground Plane Principle . . . . . . . . . . . . . . . . . . . . . |
2-3 |
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Extending the Ground Plane Principle . . . . . . . . . . . . . . |
2-5 |
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Grounding a PCB to the Drive Chassis . . . . . . . . . . . . . |
2-5 |
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Noise Solutions Using the Ground Plane Principle . . . . . . . |
2-6 |
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Grounding to the Component Mounting Panel. . . . . . . . |
2-6 |
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Doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-7 |
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Adjacent Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-8 |
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Grid and Raised Floor. . . . . . . . . . . . . . . . . . . . . . . . . . |
2-9 |
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Mezzanine Floor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-10 |
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Machine Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-11 |
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New Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-12 |
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Existing Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-13 |
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Limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
2-13 |
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Grounding (Safety Earth) . . . . . . . . . . . . . . . . . . . . . . . . . |
2-14 |
Publication GMC-RM001A-EN-P — July 2001
ii Table of Contents
Chapter 3 |
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Segregating Sources and Victims 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 |
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Chapter 4 |
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Shielding Wires, Cables, and |
Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
4-1 |
Components |
Understanding the Shielding Concept . . . . . . . . . . . . . . . . . |
4-1 |
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Ferrite Sleeves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
4-2 |
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Ferrite Sleeve Limitations. . . . . . . . . . . . . . . . . . . . . . . . |
4-4 |
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Mixing Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
4-4 |
Chapter 5
Filtering Noise |
Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . . 5-1 |
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Understanding the Filtering Concept . . . . . . . . . . . . . . . |
. . . 5-1 |
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Commercial AC Line Filters for Low Voltage Circuits |
. . . 5-1 |
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General Purpose 0-24V ac/dc Filters . . . . . . . . . . . . |
. . . 5-2 |
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Filter Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . . 5-3 |
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Performance Test Set-up . . . . . . . . . . . . . . . . . . . . . |
. . . 5-4 |
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Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . . 5-4 |
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Ultrasonic Transducers . . . . . . . . . . . . . . . . . . . . . . . . . |
. . . 5-5 |
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Xenon Flashing Beacons (strobe lights). . . . . . . . . . . . . . |
. . 5-5 |
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AC Line Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . 5-5 |
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Earth Leakage/Ground Fault . . . . . . . . . . . . . . . . . . . |
. . 5-6 |
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Chapter 6 |
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Contact Suppression |
Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . 6-1 |
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Understanding Contact Suppression for AC Circuits . . . . . |
. . 6-1 |
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Methods of AC Contact Suppression . . . . . . . . . . . . . |
. . 6-2 |
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Understanding Contact Suppression for 24V dc Circuits . . |
. . 6-3 |
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Methods of DC Contact Suppression . . . . . . . . . . . . . |
. . 6-3 |
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Contact Suppression Effects . . . . . . . . . . . . . . . . . . . . . . |
. . 6-4 |
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Chapter 7 |
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Power Distribution |
Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . 7-1 |
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Understanding Noise in Power Wiring . . . . . . . . . . . . . . |
. . 7-1 |
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Three-Phase Power Supplies. . . . . . . . . . . . . . . . . . . . . . |
. . 7-1 |
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Line Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . 7-1 |
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Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . 7-3 |
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Single Phase Power Supplies . . . . . . . . . . . . . . . . . . . . . |
. . 7-4 |
Publication GMC-RM001A-EN-P — July 2001
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Table of Contents |
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24V dc Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . |
7-4 |
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24V dc Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . |
7-5 |
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24V dc PSU Zoning Methods. . . . . . . . . . . . . . . . . . . . . |
7-5 |
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Linear PSU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
7-9 |
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Special Applications for 24V dc PSUs . . . . . . . . . . . . . |
7-11 |
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Chapter 8 |
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Motor Wiring |
Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
8-1 |
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Understanding Noise in Motor Power Wiring . . . . . . . . . . . |
8-1 |
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Shielding Motor Power Cables . . . . . . . . . . . . . . . . . . . . . . |
8-2 |
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Grounding Motor Power Cable Shields . . . . . . . . . . . . . . . . |
8-2 |
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Applying Ferrite Sleeves. . . . . . . . . . . . . . . . . . . . . . . . . . . |
8-3 |
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Splicing Motor Power Cables . . . . . . . . . . . . . . . . . . . . . . . |
8-3 |
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Handling Excess Cable. . . . . . . . . . . . . . . . . . . . . . . . . . . . |
8-4 |
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Installing Long Motor Cables . . . . . . . . . . . . . . . . . . . . . . . |
8-4 |
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Chapter 9 |
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High Speed Registration Inputs |
Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-1 |
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Understanding Registration Inputs . . . . . . . . . . . . . . . . . . . |
9-1 |
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Noise Reduction Methods. . . . . . . . . . . . . . . . . . . . . . . . . . |
9-2 |
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Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-2 |
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Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-2 |
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Shared Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-2 |
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Dedicated Power Supply. . . . . . . . . . . . . . . . . . . . . . . . |
9-4 |
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Detection Device Mounting. . . . . . . . . . . . . . . . . . . . . . |
9-4 |
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Proximity Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-5 |
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Signal Noise Filter Options . . . . . . . . . . . . . . . . . . . . . . . . . |
9-5 |
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Single Voltage Input (24V or 5V). . . . . . . . . . . . . . . . . . |
9-6 |
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Dual Voltage Inputs (24V or 5V) . . . . . . . . . . . . . . . . . . |
9-7 |
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Registration Error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-8 |
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Error Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-9 |
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Software Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
9-9 |
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Chapter 10 |
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Encoders |
Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
10-1 |
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Understanding Encoders . . . . . . . . . . . . . . . . . . . . . . . . . |
10-1 |
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Noise Reduction Methods. . . . . . . . . . . . . . . . . . . . . . . . . |
10-1 |
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Driver Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
10-1 |
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Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
10-2 |
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Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
10-2 |
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Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
10-2 |
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Power Supply Wiring Options . . . . . . . . . . . . . . . . . . . . . |
10-3 |
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Chapter 11 |
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Measuring Noise Reduction |
Chapter Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
11-1 |
Effectiveness |
Understanding Noise Measurement. . . . . . . . . . . . . . . . . . |
11-1 |
Publication GMC-RM001A-EN-P — July 2001
iv Table of Contents
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Methods for Measuring Noise . . . . . . . . . . . . . . . . . . . . . . |
11-1 |
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Measuring Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
11-2 |
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Oscilloscope Specifications . . . . . . . . . . . . . . . . . . . . . |
11-2 |
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Oscilloscope Settings for Measuring Noise Peaks . . . . . |
11-2 |
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E-Field Sniffing Method . . . . . . . . . . . . . . . . . . . . . . . . |
11-3 |
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H-Field Sniffing Method . . . . . . . . . . . . . . . . . . . . . . . |
11-4 |
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Direct Voltage Measurement Method . . . . . . . . . . . . . . |
11-4 |
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Grounding Your Probe (reference ground) . . . . . . . . . |
11-6 |
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Ground Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
11-7 |
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Differential Measurements . . . . . . . . . . . . . . . . . . . . . . |
11-7 |
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Scope Probe Lead Extension . . . . . . . . . . . . . . . . . . . . |
11-9 |
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Checking Your Method for Effectiveness . . . . . . . . . . . |
11-9 |
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Identifying the Noise Source . . . . . . . . . . . . . . . . . . . |
11-10 |
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Intermittent Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . |
11-10 |
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General Guidelines for Measuring Noise . . . . . . . . . . . . . |
11-10 |
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What are Acceptable Noise Levels? . . . . . . . . . . . . . . |
11-10 |
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Field Strength Meters . . . . . . . . . . . . . . . . . . . . . . . . |
11-11 |
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Monitoring for Noise. . . . . . . . . . . . . . . . . . . . . . . . . |
11-11 |
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Appendix A |
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Noise Control Supplement |
Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. A-1 |
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Grounding Cable Shields . . . . . . . . . . . . . . . . . . . . . . . . . |
. A-1 |
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Pigtails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. A-1 |
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Clamping at the Circular Section . . . . . . . . . . . . . . . . . |
. A-2 |
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Wire Segregation Test Results . . . . . . . . . . . . . . . . . . . . . . |
. A-5 |
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Test Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. A-5 |
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Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. A-6 |
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Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. A-7 |
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Switch-Mode DC Power Supplies . . . . . . . . . . . . . . . . . . . |
. A-8 |
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Background Information . . . . . . . . . . . . . . . . . . . . . . . |
. A-8 |
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Grounding the Common . . . . . . . . . . . . . . . . . . . . . . . |
. A-9 |
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DC Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
A-11 |
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Positioning the PSU within the Panel . . . . . . . . . . . . . . |
A-11 |
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AC Line Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
A-12 |
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Using Separate DC Power Supplies . . . . . . . . . . . . . . . |
A-12 |
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Using a Dynamic Braking Contactor . . . . . . . . . . . . . . . . . |
A-13 |
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Reducing Dynamic Braking Circuit Noise . . . . . . . . . . . |
A-14 |
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Bonding Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
A-15 |
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Wire Forms an Antenna . . . . . . . . . . . . . . . . . . . . . . . |
A-15 |
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Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
A-15 |
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Noise Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
A-16 |
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Appendix B |
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EMC Product Suppliers |
EMC Product Suppliers. . . . . . . . . . . . . . . . . . . . . . . . . . . |
. B-1 |
Publication GMC-RM001A-EN-P — July 2001
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
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 |
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The contents of this manual are described in the table below.
Chapter |
Title |
Contents |
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Preface |
Describes the purpose, background, and |
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scope of this manual. Also specifies the |
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audience for whom this manual is |
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intended. |
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1 |
Electrical Noise Control |
Provides a brief understanding of the need |
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Overview |
for electrical noise control, how noise |
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affects system performance, noise |
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coupling methods, and solutions. |
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2 |
High Frequency (HF) Bonding |
Describes the ground plane principle and |
|
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provides techniques for bonding devices, |
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panels, machines, floors, doors, and |
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buildings. |
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3 |
Segregating Sources and |
Describes how establishing zones within |
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Victims |
your system for noise sensitive or noise |
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generating components can reduce |
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electrical noise coupling. |
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4 |
Shielding Wires, Cables, and |
Describes how using shielded cable or |
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Components |
steel shields can reduce electrical noise. |
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5 |
Filtering Noise |
Describes how low-pass filters and ferrite |
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sleeves can reduce electrical noise. |
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6 |
Contact Suppression |
Describes how contact suppressors for |
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relays and various other switches can |
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7 |
Power Distribution |
Describes bonding, segregating, shielding, |
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and filtering techniques for use when |
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routing AC and DC power. |
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8 |
Motor Wiring |
Describes shielding, grounding, and |
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splicing techniques for use with motor |
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wiring. |
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9 |
High Speed Registration |
Describes how wiring sensitive to |
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Inputs |
electrical noise benefits from proper noise |
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reduction strategies. |
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10 |
Encoders |
Describes bonding, segregating, shielding, |
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and filtering techniques for use with |
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encoders. |
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11 |
Measuring Noise Reduction |
Describes the equipment, methods, and |
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Effectiveness |
various guidelines for measuring noise |
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levels and noise reduction effectiveness. |
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Appendix A |
Noise Control Supplement |
Provides background information on |
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specific topics related to electrical noise |
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control. |
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Appendix B |
EMC Product Suppliers |
Provides a list of EMC product suppliers, |
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the products they offer, and internet |
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website. |
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Publication GMC-RM001A-EN-P — July 2001
Preface |
P-3 |
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The following documents contain additional information related to electrical noise control. To obtain a copy, contact your local Allen-Bradley office or distributor.
For: |
Read This Document: |
Document Number: |
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Specific advice on motion products |
Noise Control Supplement - Motion Products |
GMC-RM002x-EN-P1 |
Advice specific to large systems |
Industrial Automation Wiring and Grounding Guidelines for Noise |
1770-4.1 |
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Immunity |
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Advice specific to large systems |
Installing, Operating and Maintaining Engineered Drive Systems |
D2-3115-2 |
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(Reliance Electric) |
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Safety advice |
Safety Guidelines for the Application, Installation, and |
SGI-1.1 |
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Maintenance of Solid-State Control |
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IEEE industry standards for electrical |
IEEE Guide for the Installation of Electrical Equipment to |
IEEE 518 |
equipment installation |
Minimize Electrical Noise Inputs to Controllers from External |
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Sources |
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A text book on noise reduction techniques |
Noise Reduction Techniques in Electronic Systems |
N/A |
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Henry W. Ott |
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Published by Wiley-Interscience |
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A text book on grounding techniques for the |
Grounding for the Control of EMI |
N/A |
control of EMI |
Hugh W. Denny |
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Published by Don White Consultants |
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A text book on solving interference problems |
Solving Interference Problems in Electronics |
N/A |
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Ralph Morrison |
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Published by Wiley-Interscience |
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A technical paper on EMI emissions |
EMI Emissions of Modern PWM ac Drives |
N/A |
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Gary L. Skibinski, Russel J. Kerkman, & Dave Schlegel |
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IEEE Industry Applications Magazine, Nov./Dec. 1999 |
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A text book on EMC |
EMC for Product Designers |
N/A |
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Tim Williams |
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Published by Newnes |
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1Available in future. Check with The Automation Bookstore.com or your Allen-Bradley sales representative for documentation availability.
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.
Publication GMC-RM001A-EN-P — July 2001
P-4 |
Preface |
|
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Publication GMC-RM001A-EN-P — July 2001
Chapter 1
Electrical Noise Control Overview
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).
In Europe, a system must satisfy EMC regulations. It must also work reliably without suffering from noise-induced failures.
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 specified level.
•Potential victims of noise must be hardened to withstand a higher noise level.
Publication GMC-RM001A-EN-P — July 2001
1-2 |
Electrical Noise Control Overview |
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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.
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.
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.
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.
Publication GMC-RM001A-EN-P — July 2001
Electrical Noise Control Overview |
1-3 |
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•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
AC |
+24V |
No load connected |
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24V dc PSU |
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DC common |
Noise voltage |
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Ground Plane - conductive metal panel
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
8
6
4
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0
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6.0V pk -6
-8
-10V
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0 |
1 |
2 |
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4 |
5 |
6 |
7 |
8 |
9 ms |
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 |
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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
100 pF = 200 Ω 1
@ 10 MHz
50 Ω
Victim TTL gate receives 1.2V spikes
Signal Source (zero impedance)
1Refer to the section Capacitance below for an explanation of the 200 ohm impedance. Generally, most potential victims are better protected than this.
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.
Noise is conducted directly by system power wiring. A common route for conducted noise is the 24V dc distribution wiring.
Publication GMC-RM001A-EN-P — July 2001
Electrical Noise Control Overview |
1-5 |
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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 |
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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 H (Micro Henry). At 10 MHz the impedance is 60 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
Circuit A
Stray inductance
Magnetic coupling |
Separation distance |
Circuit B
Publication GMC-RM001A-EN-P — July 2001
1-6 |
Electrical Noise Control Overview |
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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.
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.
This method: |
In this |
Is defined as: |
For more |
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information refer to: |
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HF (high frequency) |
Coupling |
Maintaining all metalwork at the same electrical potential. This |
The chapter High |
Bonding |
Reduction |
method is low cost and the basis for all other methods. It works by |
Frequency (HF) |
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ensuring all equipment chassis are at the same potential at all |
Bonding. |
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frequencies. If different potentials exist the voltage difference is |
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seen as common-mode noise on all interconnecting wiring. |
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Segregation |
Coupling |
Separating sources and victims of electrical noise into zones. Noise |
The chapter |
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Reduction |
coupling reduces with the square of separation distance. Zoning is |
Segregating Sources |
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zero cost (within limits). |
and Victims. |
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Shielding |
Coupling |
Using shielded cable and steel barriers (Faraday cage effect) to |
The chapter Shielding |
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Reduction |
reduce electrical noise. Because of its relatively high cost, shielding |
Wires, Cables, and |
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is used with discretion. |
Components. |
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Filtering |
Coupling |
Using low-pass filters to attenuate RF noise. Relatively low cost but |
The chapter Filtering |
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Reduction |
impractical for every wire. |
Noise. |
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Contact |
Source |
Adding contact suppression to mechanical switches to reduce noise. |
The chapter Contact |
Suppression |
Reduction |
Generally, the one noise source directly influenced by the system |
Suppression. |
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builder. |
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Publication GMC-RM001A-EN-P — July 2001
Electrical Noise Control Overview |
1-7 |
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Implementation involves applying the methods summarized in the table on page 1-6 to the applications as shown in the table below.
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This application: |
Is defined as: |
For more |
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information refer to: |
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Routing AC and DC |
Applying bonding, segregating, shielding, and filtering techniques to |
The chapter Power |
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power |
AC and DC power supplies and the associated wiring. |
Distribution. |
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Routing motor |
Applying shielding, grounding, and splicing techniques to motor |
The chapter Motor |
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power cables |
power cable installation. |
Wiring. |
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Wiring high speed |
Applying all the noise reduction methods available to improve the |
The chapter High |
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registration inputs |
performance of noise sensitive wiring. |
Speed Registration |
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Inputs. |
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Routing encoder |
Applying bonding, segregating, shielding, and filtering techniques to |
The chapter Encoders. |
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power cables |
encoder installation. |
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Measuring Effectiveness |
Measuring noise reduction effectiveness involves using an |
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oscilloscope to test for noise during implementation. It also involves |
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monitoring for noise after implementation should updates to the |
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system affect system performance. |
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This application: |
Is defined as: |
For more |
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information refer to: |
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Measuring |
Testing for electrical noise during implementation, identifying the |
The chapter |
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effectiveness |
sources of noise, determining acceptable noise levels, and |
Measuring Noise |
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monitoring for noise on an on-going basis. |
Reduction |
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Effectiveness. |
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Publication GMC-RM001A-EN-P — July 2001
1-8 |
Electrical Noise Control Overview |
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Publication GMC-RM001A-EN-P — July 2001
Chapter 2
High Frequency (HF) Bonding
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:
•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 |
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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 |
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+600V dc |
Motor |
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capacitance |
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Publication GMC-RM001A-EN-P — July 2001
High Frequency (HF) Bonding |
2-3 |
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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
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Many other noise sources exist in a typical system and the advantage of good bonding holds true for all.
The purpose of High Frequency (HF) bonding is to present a defined low impedance path for HF noise currents returning to their source.
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Noise current must and will return to source. If a safe |
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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.
Publication GMC-RM001A-EN-P — July 2001
2-4 |
High Frequency (HF) Bonding |
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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
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Insulation
layer Interconnect layer
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 |
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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.
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
PCB copper interconnection layer
PCB copper ground plane layer
bonded to drive chassis
Printed circuit board (PCB)
Guidelines for the system builder include:
•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 |
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Noise Solutions Using the
Ground Plane Principle
In this section, examples of how to apply the ground plane principle are described.
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
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
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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.
For doors 2 m (78 in.) in height, bond with two or three (three is preferred) braided straps (top, bottom, and center).
EMC seals are not normally required for industrial systems.
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Bond adjacent panels by mounting multiple flat straps between the panels. As an alternative, mount a filler plate between the panels using multiple fasteners along the edges of the plate.
Figure 2.6
Panel ground plane extended to adjacent panels
Adjacent panels bonded to extend the ground plane
Cabinet ground plane (component mounting panel)
Ground plane extended to side panel by bonding to main panel
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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
Grid ground plane. Copper strip laid on the floor, covered by a false floor (also bonded to machine structure).
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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
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Machine structure |
Machine structure used as ground plane |
bonded to floor |
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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
Panel ground plane bonded to structure ground plane by clean and dirty wireways
Bond the panel(s) to the machine structure as tight as possible, but if this proves difficult, construct a low impedance path using the following guidelines:
•Use a zinc-plated tray, as wide as practical, and join sections by overlapping with several fasteners across the width. The perforations will not reduce performance (refer to Figure 2.10).
•EMC trunking (plated at joint surfaces with conductive gaskets) also makes a good bond.
•Short and wide is the requirement for any HF bonding material. Panel(s) should be located as close to the machine structure as practical and the bond should be firmly attached at both the machine structure and the control panel (not the cabinet outer panels).
•Multiple trays/trunking are better.
Note that copper wire safety earth bonding is still required. Refer to the section Grounding (Safety Earth) at the end of this chapter for more information.
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Figure 2.10
Extending the panel ground plane using cable tray
Multiple fasteners
Zinc plated steel main panel
Same width
Must be directly bonded here and at the machine structure
Zinc plated steel cable tray (wider is better)
Note: A ground plane does not have to be flat.
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.
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
Cabinet ground plane (panel) bonded to nearest building steel
Building ground plane. Copper strip laid into the floor bonding columns together.
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