DEWESOFT V21-1 User manual
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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●The inputs must not, unless otherwise noted (CATx identification), be connected to the main
circuit of category II, III and IV.
●The power cord separates the system from the power supply. Do not block the power cord, since
it has to be accessible for the users.
●DO NOT use the system if equipment covers or shields are removed.
●If you assume the system is damaged, get it examined by authorized personnel only.
●Adverse environmental conditions are Moisture or high humidity Dust, flammable gases, fumes
or dissolver Thunderstorm or thunderstorm conditions (except assembly PNA) Electrostatic
fields, etc.
●The measurement category can be adjusted depending on module configuration.
●Any other use than described above may damage your system and is attended with dangers like
short-circuiting, fire or electric shocks.
●The whole system must not be changed, rebuilt or opened.
●DO NOT operate damaged equipment: Whenever it is possible that the safety protection
features built into this product have been impaired, either through physical damage, excessive
moisture, or any other reason, REMOVE POWER and do not use the product until the safe
operation can be verified by service-trained personnel. If necessary, return the product to
Dewesoft sales and service office for service and repair to ensure that safety features are
maintained.
●If you assume a more riskless use is not provided anymore, the system has to be rendered
inoperative and should be protected against inadvertent operation. It is assumed that a more
riskless operation is not possible anymore if the system is damaged obviously or causes strange
noises. The system does not work anymore. The system has been exposed to long storage in
adverse environments. The system has been exposed to heavy shipment strain.
●Warranty void if damages caused by disregarding this manual. For consequential damages, NO
liability will be assumed!
●Warranty void if damage to property or persons caused by improper use or disregarding the
safety instructions.
●Unauthorized changing or rebuilding the system is prohibited due to safety and permission
reasons (CE).
●Be careful with voltages >25 VAC or >35 VDC! These voltages are already high enough in order to
get a perilous electric shock by touching the wiring.
●The product heats during operation. Make sure there is adequate ventilation. Ventilation slots
must not be covered!
●Only fuses of the specified type and nominal current may be used. The use of patched fuses is
prohibited.
●Prevent using metal bare wires! Risk of short circuit and fire hazard!
●DO NOT use the system before, during or shortly after a thunderstorm (risk of lightning and high
energy over-voltage). An advanced range of application under certain conditions is allowed with
therefore designed products only. For details please refer to the specifications.
●Make sure that your hands, shoes, clothes, the floor, the system or measuring leads, integrated
circuits and so on, are dry.
●DO NOT use the system in rooms with flammable gases, fumes or dust or in adverse
environmental conditions.
●Avoid operation in the immediate vicinity of high magnetic or electromagnetic fields,
transmitting antennas or high-frequency generators, for exact values please refer to enclosed
specifications.
●Use measurement leads or measurement accessories aligned with the specification of the
system only. Fire hazard in case of overload!
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●Do not switch on the system after transporting it from a cold into a warm room and vice versa.
The thereby created condensation may damage your system. Acclimatise the system unpowered
to room temperature.
●Do not disassemble the system! There is a high risk of getting a perilous electric shock.
Capacitors still might be charged, even if the system has been removed from the power supply.
●The electrical installations and equipment in industrial facilities must be observed by the security
regulations and insurance institutions.
●The use of the measuring system in schools and other training facilities must be observed by
skilled personnel.
●The measuring systems are not designed for use in humans and animals.
●Please contact a professional if you have doubts about the method of operation, safety or the
connection of the system.
●Please be careful with the product. Shocks, hits and dropping it from already- lower level may
damage your system.
●Please also consider the detailed technical reference manual as well as the security advice of the
connected systems.
●This product has left the factory in safety-related flawlessness and in proper condition. In order to
maintain this condition and guarantee safety use, the user has to consider the security advice
and warnings in this manual.
EN 61326-3-1:2008
IEC 61326-1 applies to this part of IEC 61326 but is limited to systems and equipment for industrial
applications intended to perform safety functions as defined in IEC 61508 with SIL 1-3.
The electromagnetic environments encompassed by this product family standard are industrial, both
indoor and outdoor, as described for industrial locations in IEC 61000-6-2 or defined in 3.7 of IEC 61326-1.
Equipment and systems intended for use in other electromagnetic environments, for example, in the
process industry or in environments with potentially explosive atmospheres, are excluded from the
scope of this product family standard, IEC 61326-3-1.
Devices and systems according to IEC 61508 or IEC 61511 which are considered as “operationally
well-tried”, are excluded from the scope of IEC 61326-3-1.
Fire-alarm and safety-alarm systems, intended for the protection of buildings, are excluded from the
scope of IEC 61326-3-1.
Documentation version history
V20-1 12/12
Version
Date
Notes
V20-1
29-12-2020
New template
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