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Electrical issues with multi current shunt measure

Benjamin.vial Apr 9, 2024 06:09 AM


I'm trying to build a little test bench to get the current consumption of several field works devices, with a shunt resistor circuit.

Here is a  scheme of my assembly

Description :

I have 4 power supply, plugged on the french electrical network, each of them give 12,5 VDC.

Measured system 1 : Trimble Alloy GNSS receiver, a "simple" electrical load with an antenna. (awaited <10W consumption)

Measured system 2 : Digos Cube seismological digitizer (awaited <10W consumption)

Measured system 3 : Campbell CR300 with a 3G ercogener modem (=wavecom / fastrack) supplied by the SW12.(awaited <10W consumption)

The 3 systems have shunt resistor (R1, 2 & 3) that is calibrated to have a 50mV voltage for 50A current.

The CR1000 is programmed with 3 VoltSE function (very basic program).

The CR1000 have a NL120 plugged on a RJ45 switch, itself connected to a 230Vac power supply.

The problems :

If I use each system alone, I can easily retrieve the voltage and estimate consumption. But 2 or 3 systems together, and VoltSE become incoherent and sometime negative, measured devices can rebooting, measure could vary with or without the ground plugged on the CR1000 and I can read something about 45Vdc between the CR1000 ground connector and the "real" ground.

So, first I stopped everything, because I am afraid to damage the all stuff, there is something I missing here.

I conclude that 1H, 2H and 3H are somehow connected and there is current circulate inside the CR1000 and goes on a device or another, distorting the measures.

But I can't explain the extreme voltage I've seen on some measure ; how the power supplies coould been in series somewhere to get there voltage summed ?

I know it seem a bit complicated but, somebody have an idea to help me there ?

Benjamin.vial Apr 22, 2024 06:32 AM


it seem that interferences are resolved by using a differential voltage measure, in order to avoid the common ground plugging.


LuciusFishman May 20, 2024 06:45 PM

This post is under review.

cristommy May 21, 2024 09:38 AM

This post is under review.

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