After looking at the CST flow sensor, I am not sure how to interface to it. It looks like a two wire sensor where you bias the two leads with a power supply (8-35 VCD) and then they indicate the output is a voltage on the same two wires. It seems to make more sense to me that it would be a current and not a voltage, at least that is what I concluded with the Hunter flow sensor.
Do you own one of these sensors? If you do and have access to a voltage controlled power supply and an ammeter ad volt meter then you could run the same experiments that I did for the Hunter flow sensor to get a better idea of how it works. Or you could call them since they seem to be more open that Hunter at sharing information.