Thank you @György-Farkas for detailed answer. I've tried this ADC (on demo board) on Arduino and also received nothing. I think that this board is broken. I bought ADS1115 and now I can smoothly read from photodiode If somebody will need that in future guys from Control Everything Community made working python example for Omega2. (or at least it's working in my case with FW: 0.2.0 b191)