I am looking for a good example design of the above. I noticed that many industrial designs specify 24VDC for inputs/outputs and up to 500 mA drive capacity. It also seems that there is no standard on how sources/loads are connected. So, I would appreciate to see some typical solutions.
There is no standard since opto-isolators vary in design, performance, and whether the output is AC or DC, and thus the design, using the isolator, is tailored to the particular application requirements. If you look in the data sheet of a particular isolator, it will often give examples of how to use the circuit. A Google search will give you some opto-isolator circuit examples.
I understand that there is no standard. And I am not looking for how to use an opto. I am looking for a typical industrial design of a 24VDC input/output. Thanks.