1. Which would be the best point to ground the shield of the ADC signal input cable : Power Earth or ADC Com ?
At one end ONLY, closest to the best ground you have

2. Because of the PC, there is a link established between the Power Earth and the ADC Com. Is this OK or is to be avoided by some means ? The Power Earth is a dedicated earth NOT linked with the Neutral.
A very usual case, the suggestion below will handle it. The problem is that I have seen just about anything masking under the name of 'ground'. You will be better off isolating between the 'signal conditioner' and the '232 out unit', than isolating between the '232 out unit' and the PC.


The above are specific queries, but if the members find something basically wrong with the setup then such comments are most welcome. (Just because it is working I can't say its perfect . I want to know what would be BETTER than this )
There is nothing "basically wrong with the setup", however, Since digital data is much easier to protect from noise (and can be checksummed), I would move the ADC to the 'signal conditioner' and transfer digital data. A very economical way to do this would be to use a V/F converter. I would, however, use a <$1 '51 derivative and use 2 isolated RS-485 transcievers (<$4 from MAX) to communicate.


Just because it is working I can't say its perfect very wise words

State what resolution you need from the A/D and maybe I will have a better suggestion.

Is this at the design phase or is it further along?

Erik