To restate what Kephra said a different way, there is NO piece of equipment you can buy that will read the PPM of either ionic nor colloidal silver (either at all or definitely not properly).
The ONLY way to tell what PPM you made is to use the current limiter at a fixed current and to calculate the run time based on Faraday's law, run at that current for that amount of time, shut the cell down and believe you have the target PPM (because you do!).
This is not a leap of faith. Kephra verified Faraday's law for the manufacture of ionic silver. The equation works!