GROUND FAULT
13 MARCH 2023

Hi Duane,

hope you are doing well. I have some time out here so I'm able to work on some of the basic stuff for the new MVC.

I'd like to build a test board for a ground fault system that seems simple but sufficient. I attached a kicad schematic but also just a pdf in case you can't read those.

The idea is to put a -15V potential on the seawater ground and then measure if current flows into that ground. Since all voltages we have in the systems are referenced to the same ground and they are all different from -15V, we can see ground faults for all wires we have.
For the few things we have that are on truly isolated ports, we can have a switch that temporarily connects the bus ground with that isolated ground during the GF measurement.
 
I think I figured out the mechanics of measuring these small currents and invert the voltage so it can be measured with a MCU. It would be good if you have a look at that and see if you think I missed something.

For the test board I'm thinking of having an input with something like 12V to generate all the voltages required for the board, an RS232 interface to talk to MCU and a line that can be sourced with a random voltage. On the other side, we have a seawater ground that we can hang into the tank and the line with the random voltage which could be an old wetcable with a bad dummy on it so we can generate some ground faults. First test would of course be just some high value resistors.

Once we have a board, we can get Cole on writing software for the micro which basically just triggers the relay and the ground fault test and then samples the voltage from the op amp. It might make sense to put some test jumpers on there such that one can actually measure the current with a meter so we can do some calibration.

Let me know if you have any questions or issues with this.

Thanks
Erik