Last year I was looking at using an Orb sensor to measure chlorine. This is suppoed to measure sanitizer in the water, which would correlate to free Cl, but it would not be an exact measure of free CL.
I don't have a couple K for a free CL probe.
I decided to just stay with the manual method, but it seems like it could be done.
But, one thing I found out while I was looking into these things is that they are like special batteries, but their voltage changes depending on the ph or sanitizer levels in the water. That means, like batteries, they have a limited life, I think a year or two.
Gets pretty expensive when you factor that in.
To do this, you would need to install a sensor or two in the pipes of your system, connect the sensor to a buffer circuit, connect that to a A to D converter, connected to a PC somewhere.
Randy