Unique situation where I'm trying to find a way to detect a titanium ball moving through a water filed stainless steel pipe (~ 1 inch).
-pipe is water filled
-ball moving up to 3 ft per second
- ball will be considerably hotter than piping
Thanks for all suggestions!
At Westinghouse (ITI MOVATS, now Crane Nuclear), we developed a pulsed eddy-current system to measure the position of the SS disk in a SS check valve. The initial system was developed by Roy Ricci of Intex, Inc. It used 2 transmitter-sensors, each an air coil w/ send and receive coil. Roy said the design was based on high-end metal detectors. The raw signal was the difference between receiving coils, placed at each end of travel. It was integrated (search IVC102) over an optimum time interval, dependent on the thickness and material (304, 316, or 400 series stainless). I determined the optimal intervals by stroking valves in air. The sending coil was simply charged up, then the current abruptly stopped to form the magnetic pulse. The Motorola MGP20N40 was the best switch found (1990's), but probably better ones today (lower ON resistance, higher clamp voltage, protected input).
Penetrating the wall is easiest if non-magnetic. 400 series acted ~50% thicker than 300 series stainless. The "magnetic thickness" determined the optimal time to capture the return pulse. I recall 25 Hz pulses was best for 1" thick 300 series walls and faster for thinner walls. So your 3 ft/sec speed in thin tubing "should work". A ferrous check-valve disk would probably be easier to detect than the stainless. We never tried aluminum, which is paramagnetic (repels a field), and titanium might be similar. But, I expect it would give a signal, and actually more disruptive than stainless.
Re leveraging above, you might be able to buy used parts on ebay since the nuclear plant customers are closing. Search "checkmate" and "MOVATS". If you develop your own system, you can use internally, but if sold to customers you may need to license patents from Intex or Crane.