DEWESOFT V21-1 Manuale utente
Power supply ground
loops
USER MANUAL
Power supply ground loops V21-1
1
Power supply ground loops
USER MANUAL
1. Table of contents
1. Table of contents 2
2. About this document 3
2.1. Legend 3
3. Overview 4
4. Detailed description 4
4.1. Supply topology 4
4.2. Error case with broken GND cable 5
4.3. Error case with not symmetric supply line resistor 5
5. Solution 6
5.1. Supply protection box 6
5.2. Isolated power supply 7
6. Warranty information 8
Calibration 8
Support 8
Service/repair 8
Restricted Rights 8
Printing History 9
Copyright 9
Trademarks 9
7. Safety instructions 9
Safety symbols in the manual 9
General Safety Instructions 9
Environmental Considerations 10
Product End-of-Life Handling 10
System and Components Recycling 10
General safety and hazard warnings for all Dewesoft systems 10
Documentation version history 12
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2. About this document
This is the application note about the power supply ground loops.
2.1. Legend
The following symbols and formats will be used throughout the document.
Important
It gives you important information about the subject.
Please read carefully!
Hint
It gives you a hint or provides additional information about a subject.
Example
Gives you an example of a specific subject.
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3. Overview
Ground loops in signal lines are well known in data acquisition systems. Measurement errors, higher
noise or even damage of the DAQ-System or the connected sensors are the result of these GND-Loops.
But what about the power supply? Are GND-loops possible there as well? Yes, it is exactly the same at
non isolated power supply concepts! Care must be taken when supplying multiple devices – even if each
device itself has a correct over-voltage and reverse polarity protection like the complete DAQ-System
series from Dewesoft (like Sirius, DEWE-43…).
This is the price for higher efficiency and wider input range of non isolated power supplies.
4. Detailed description
4.1. Supply topology
The picture below shows a typical configuration. A sensor and the DAQ-System are supplied
out by the same DC power supply (e.g. the vehicle on board network). You can see that the GND is
connected from two points: The main current flows along the blue thick line (“high current
path”), to the load and back. But the GND of both devices are also connected together,
through the sensor output and DAQ input.
Image 1: A typical sensor supply configuration
Hint
In general, this supply configuration is also valid connecting two DAQ systems together. The
additional connection may be also something else than the sensor input: e.g. be the common
GND of the data path (USB-GND) or the common GND of the sync bus.
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4.2. Error case with broken GND cable
You can imagine what will happen when the “high-current path” is open. The current will flow a
different way. Now the return supply path of the sensor is routed through the GND of the sensor input
from the DAQ device.
Image 2: Error case with broken GND cable
Important
Usually the internal circuitry is not capable of driving this high current. So the DAQ device may
be damaged.
4.3. Error case with not symmetric supply line resistor
In practice the supply wiring is more complicated like shown in this basic diagram. A cable brake on the
supply line is for sure the worst case. But also line resistances in the supply lines combined with different
supply current levels will cause unintentional current flow through the DAQ-system like shown below.
Image 3: Asymmetric supply line
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5. Solution
5.1. Supply protection box
An external fuse in the GND line solves this problem already. If the current through the supply line is too
high, the fuse will blow. Therefore no damage on the DAQ-system or the sensor may happen.
Image 4: The external fuse in the GND line
In addition the supply protection box provides reverse polarity protection. The current is shorted over
the diode (failure current does not flow through the sensor) and will blow up the fuse.
Image 5: Reverse polarity protection
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5.2. Isolated power supply
Another way of protecting the DAQ device is the usage of the “DS isoPower 75W”. This box includes a
DC/DC converter which galvanically isolates the power supply input of the DAQ System (the example
shows the DEWE-43 V). Due to the isolation, no error current is possible through the supply line.
Image 6: Galvanically isolated power supply
The final result is the same: reverse polarity protection of the supply line.
Hint
This isolated power supply device is useful only with an older hardware. All new Dewesoft
devices have the power supply input isolated.
DEWE-43 Hardware revisions:
V20-1 7/12
DEWE-43 V
Initial version
DEWE-43 A
Added isolated CAN ports
DEWE-43 A ISO-POWER
Added isolated power supply
Power supply ground loops
USER MANUAL
6. Warranty information
Notice
The information contained in this document is subject to change without notice.
Note:
Dewesoft d.o.o. shall not be liable for any errors contained in this document. Dewesoft MAKES NO
WARRANTIES OF ANY KIND WITH REGARD TO THIS DOCUMENT, WHETHER EXPRESS OR IMPLIED.
DEWESOFT SPECIFICALLY DISCLAIMS THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE. Dewesoft shall not be liable for any direct, indirect, special,
incidental, or consequential damages, whether based on contract, tort, or any other legal theory, in
connection with the furnishing of this document or the use of the information in this document.
The copy of the specific warranty terms applicable to your Dewesoft product and replacement parts can
be obtained from your local sales and service office. To find a local dealer for your country, please visit
https://dewesoft.com/support/distributors.
Calibration
Every instrument needs to be calibrated at regular intervals. The standard norm across nearly every
industry is annual calibration. Before your Dewesoft data acquisition system is delivered, it is calibrated.
Detailed calibration reports for your Dewesoft system can be requested. We retain them for at least one
year, after system delivery.
Support
Dewesoft has a team of people ready to assist you if you have any questions or any technical difficulties
regarding the system. For any support please contact your local distributor first or Dewesoft directly.
Dewesoft d.o.o.
Gabrsko 11a
1420 Trbovlje Slovenia
Europe Tel.: +386 356 25 300
Web: http://www.dewesoft.com
Email: [email protected]
The telephone hotline is available Monday to Friday from 07:00 to 16:00 CET (GMT +1:00)
Service/repair
The team of Dewesoft also performs any kinds of repairs to your system to assure a safe and proper
operation in the future. For information regarding service and repairs please contact your local
distributor first or Dewesoft directly on https://dewesoft.com/support/rma-service.
Restricted Rights
Use Slovenian law for duplication or disclosure. Dewesoft d.o.o. Gabrsko 11a, 1420 Trbovlje, Slovenia /
Europe.
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Printing History
Version 2.0.0, Revision 217 Released 2015 Last changed: 23. July 2018 at 16:54.
Copyright
Copyright © 2015-2019 Dewesoft d.o.o. This document contains information which is protected by
copyright. All rights are reserved. Reproduction, adaptation, or translation without prior written
permission is prohibited, except as allowed under the copyright laws. All trademarks and registered
trademarks are acknowledged to be the property of their owners.
Trademarks
We take pride in our products and we take care that all key products and technologies are registered as
trademarks all over the world. The Dewesoft name is a registered trademark. Product families
(KRYPTON, SIRIUS, DSI, DS-NET) and technologies (DualCoreADC, SuperCounter, GrandView) are
registered trademarks as well. When used as the logo or as part of any graphic material, the registered
trademark sign is used as a part of the logo. When used in text representing the company, product or
technology name, the ® sign is not used. The Dewesoft triangle logo is a registered trademark but the ®
sign is not used in the visual representation of the triangle logo.
7. Safety instructions
Your safety is our primary concern! Please be safe!
Safety symbols in the manual
Warning
Calls attention to a procedure, practice, or condition that could cause the body injury or death
Caution
Calls attention to a procedure, practice, or condition that could possibly cause damage to
equipment or permanent loss of data.
General Safety Instructions
Warning
The following general safety precautions must be observed during all phases of operation, service, and
repair of this product. Failure to comply with these precautions or with specific warnings elsewhere in
this manual violates safety standards of design, manufacture, and intended use of the product.
Dewesoft GmbH assumes no liability for the customer’s failure to comply with these requirements.
All accessories shown in this document are available as an option and will not be shipped as standard
parts.
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Environmental Considerations
Information about the environmental impact of the product.
Product End-of-Life Handling
Observe the following guidelines when recycling a Dewesoft system:
System and Components Recycling
Production of these components required the extraction and use of natural resources. The substances
contained in the system could be harmful to your health and to the environment if the system is
improperly handled at its end of life! Please recycle this product in an appropriate way to avoid
unnecessary pollution of the environment and to keep natural resources.
This symbol indicates that this system complies with the European Union’s requirements
according to Directive 2002/96/EC on waste electrical and electronic equipment (WEEE).
Please find further information about recycling on the Dewesoft web site
www.dewesoft.com
Restriction of Hazardous Substances
This product has been classified as Monitoring and Control equipment and is outside the scope of the
2002/95/EC RoHS Directive. However, we take care of our environment and the product is lead-free.
General safety and hazard warnings for all Dewesoft systems
Safety of the operator and the unit depend on following these rules.
●Use this system under the terms of the specifications only to avoid any possible danger.
●Read your manual before operating the system.
●Observe local laws when using the instrument.
●DO NOT touch internal wiring!
●DO NOT use higher supply voltage than specified!
●Use only original plugs and cables for harnessing.
●You may not connect higher voltages than rated to any connectors.
●The power cable and connector serve as Power-Breaker. The cable must not exceed 3 meters,
the disconnect function must be possible without tools.
●Maintenance must be executed by qualified staff only.
●During the use of the system, it might be possible to access other parts of a more comprehensive
system. Please read and follow the safety instructions provided in the manuals of all other
components regarding warning and security advice for using the system.
●With this product, only use the power cable delivered or defined for the host country.
●DO NOT connect or disconnect sensors, probes or test leads, as these parts are connected to a
voltage supply unit.
●Ground the equipment: For Safety Class 1 equipment (equipment having a protective earth
terminal), a non-interruptible safety earth ground must be provided from the mains power
source to the product input wiring terminals.
●Please note the characteristics and indicators on the system to avoid fire or electric shocks.
Before connecting the system, please read the corresponding specifications in the product
manual carefully.
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