Industrial control board common ground doubt - Page 1
Forum section: electronics / beginners

author: hozone
author_rank: Regular Contributor
timestamp: December 10, 2019, 03:20:11 pm
content: Hello,I'm building a board that has to drive an industrial machine, not a big one.I've a dumb question about the ground.My boards is design in such a way that the microcontroller and logic IC is driven with one power supply; the machine low voltage sensors/motors and the output/input IC using another supply.On the current electrical cabinet all the ground are joined on main case, it means that both power supplies share the same ground of the 220V earth, they have so a common ground that is joined to the earth.Is that a good idea to have a common ground for the microcontroller and logic ICs too?Think it is, but not sure about that.Thank you!

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 10, 2019, 05:24:09 pm
content: Your control circuit (uC and logic) and load circuit (sensors and motor) must either:1) share a common ground2) have separate grounds and communicate across the galvanic isolation using opto couplers or some other isolation technology (caps or transformers)

author: hozone
author_rank: Regular Contributor
timestamp: December 10, 2019, 06:58:47 pm
content: Thank you @WimberleytechIndeed the digital I/O load circuit is separated by the mean of opto couplers.The problems and doubts arises with the 0..10v output. I should use a 0..10V signal isolator, but i prefer not to use this.I attach here a smaller schematics of the board I'm building, power circuit is exactly as you see, the output and input almost the same, they are just connected to the micro through I/O shifer IC.I think the common ground shared (GND and GND2 in my schematics) could not be an issue, but that is my question.Any suggestion appriciated.Thanks!

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 10, 2019, 07:25:00 pm
content: I see (I think)...your analog signal (0 - 10V) needs to cross the galvanic barrier (assuming separate grounds) and to do that you need an analog isolator which you want to avoid.Of course, it is hard to say without appreciating the motor and other nasty stuff on the load side, but I would go ahead and make the grounds common and see. As a backup plan, make a footprint for an analog isolator on your board and also just connect GND and GND2 at a single point so that if the common-ground plan does not work, you can separate them easily.

author: hozone
author_rank: Regular Contributor
timestamp: December 11, 2019, 07:49:45 pm
content: Thank you @WimberleytechMy board has two 0..10V output. One is connected to a motor inverter, this one is isolated. The other unluckly is connected to a magnetic powder controller, this last controller is not isolated.Unlucly I'm not expert in isolation amplifiers, I'm more a software eng. than an electronic one1) Can a design like the one attached works to you?2) I take this opportunity to ask you if you see errors on the DIGITAL_OUTPUT and DIGITAL_INPUT stage. Thank you!The actual board has a common ground and the machine works without problem, but I would like to build something a little better than the actual one.Edit: I'm also looking at a simpler optocoupler solution, using linear optocoupler. Maybe something using the 4N25 opto?