Power supply ground loops
USER MANUAL
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.
V20-1 4/12
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