Hi,


I want to build a controller for a machine with multiple sensors. The sensors are supplied with power either by the controller itself or have their own power supply. I want to galvanic separate the inputs to protect the controller against interference.

Is it enough if I galvanic isolate a common power supply for the sensor interface and the date lines from the rest of the controller, or it is better if each individual input has its own separate galvanic isolated power supply?

I have found an example of this in an application note from TI.
Industrial data-acquisition interfaces with digital isolation.
http://www.ti.com/lit/an/slyt426/slyt426.pdf

Analog Inputs:
2x 4-20 mA
2x PT100

I would be grateful for any help

 

Are you absolutely sure that Galvanic isolation is needed, this is often most necessary for safety reasons on mains or high voltage fed equipment.
In logic etc circuitry although you may have galvanic isolation, there is still the possibility of signal transference due to inductive and/or capacitive means, the alternative to this is to bond all systems commons to a central point or suitable ground plane, if done correctly this can eliminate the chances of ground loop currents occurring.
Max.

 

using fiber optic links also isolates the sensors well.
around here, we use galvanic isolation to prevent sparks and static buildup in paint areas.