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Potential Free Data Logger Connection Avoids Hardware Damage

Last updated: 2018-08-09

When working with any product from the GL Data Logger family (1) it is essential to avoid having two different (ground) potentials at the components connected to the logger. When you have two ground potentials, there is the risk of a compensating current that can damage the PCB hardware of the GL Data Logger. The following two connection examples show problematic configurations of a connected Data Logger:

Picture 1: Risky connection of data logger due to mains and car side grounded (logger mains powered)

Picture 2: Risky connection of data logger due to mains and car side grounded (logger battery powered)

Due to a different potential from the grounded mains side of the measuring equipment compared to the grounded car, there are compensating currents over the data connections (USB/CAN) that can damage the logger hardware.

How to avoid this? You must ensure that there are not two sides grounded. Best is to have no fixed potential at all.

To achieve this, it is important to use mains connection power supplies with protection class II which have no grounding as they provide potential free power on the secondary side. Here you see the icon of protection class II on a mains supply (without grounding):

Picture 3: Mains adapter of protection class II without grounding

Additionally you should avoid the car to be in direct electric connection with ground. This electric connection can happen through other car connections e.g. a grounded battery charger. Grounding could also occur through conducting connection of the metal chassis to ground (tyres are insulating and thus OK). Avoid this if possible.

The following three connection examples show safe configurations:

Picture 4: Safe connection of data logger due to mains and car side potential free (logger battery powered)

Picture 5: Safe connection of data logger due to mains and car side potential free (logger mains powered)

If no potential free mains supply is available, there is alternatively the option to:

  1. Operate a laptop computer in battery mode (without mains connection) and
  2. Take the power for the logger from the car and ECU power supply

Picture 6: Safe connection with computer working battery operated and data logger battery powered

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