Thank you for your post.
To measure flow rate may be possible, if your flow meter gives a frequency to flow conversion. You would need a unit that can measure the maximum frequency that you want to measure, then provide a scaling file to turn the freqency into flow rate.
An alternative method would be to use the flow meter and a frequency to voltage converter, then have the voltage converted in to the flow rate again using a scaling file.
You will need to source your own flow meter and frequency to voltage converter.
If you would like to provide further I will advise you on a suitable product.