I mounted the magnet that triggers the sensor on the outer perimeter of the indexing plate in my PM45 lathe that I upgraded.
It was mounted such that the magnet was spinning in a circle roughly 8-9 inches in diameter.
I had problems with very erratic operation of the sensor and display.....especially as I increased the speed.
The seller replaced it as defective.
Next one.....same problem......hmmmm.....
Finally discovered that the magnet can not be swinging such a large circle....I am assuming it moves past the sensor too quickly.
I remounted the magnet and sensor such that the magnet was spinning a 2.5" diameter path and it works great.
I took the magnet and sensor to work and mounted them on our $20,000 metal lathe to compare my speed read-out to the one on the work lathe.
I was surprised to discover that the two read the same rpm's (within one rpm of each other) UNTIL I increased the speed of the work lathe (I don't remember at what speed it began to fail...it's been a while) then THE DISPLAY ON THE WORK LATHE began to read erratically in the same manner that my setup did before I changed the mounting to a smaller diameter!
My sensor and display, however, remained rock steady....as I had mounted the magnet to a piece of stock about the same 2.5" diameter.
It was quite disappointing to discover that the rpm display on the work lathe was basically defective....by design!