We are building an instrument that goes deep underground and is connected to the surface with a long cable. Due to the length of the cable and distance between the control station and instrument we are worried about EMF and grounding causing signal disruption. We have already had problems with the magnetometer picking up stray magnetic fields from signal and power wires. In addition everything including instruments, microcontrollers, and cable is set on the same ground and we don't know if that's a good idea.

Does anybody know how to properly ground a large circuit and shield wires from stray EMF?

 

Grounding is a science in itself.
Nobody is going to write the book out for you. Nobody will even try without a drawing of your circumstances and signal levels.
Have you thought of converting your voltage signal to a current signal and running that for the long distance?
4ma to 20ma circuits are "the usual" for this.

 

All of our electronics are digital, there are no voltage or current signals. They wouldn't have the ability to reliably carry a signal over the distance we need.

The signal wires I refer to are RS485 standard. I need to know how to reduce the magnetic field around them so they don't interfere with the magnetometer readings. I'm also trying to figure out how to properly ground shielding.

I understand that nobody is going to write a book for me so I've done my homework. The problem is that most information I find is for small circuits and household appliances not large networks. I'm hoping that somebody can share their experiences with me.

 

RS485 being differential has some built in ability to reduce radiation.
If the cable is ran along the surface to the final underground source, what distance are we talking? If it is possible it might be worth either using a ground net at intervals or at least a ground rod every so many metres, If using this method, I suggest earth grounding both ends of the shielded cable.
Max.