I'm getting good signal and flow data with the Hall effect flow sensors attached to my outdoor irrigation valves, the sensors are the 3-wire (standard 5v powered / one signal wire to digital I/O pin) on Arduino, so all's fine in that world.
Flow sensors on the commercial and consumer irrigation market are 2-wire output, don't know the economics of using 2-wire instead of cheaper 3-wire Hall flow senors, you're running 2-wires from sensor to an adjacent controller. Outdoor satellite controllers have 120vac pulled into the (metal or plastic) outdoor pedestal, stepping down transformer to supply 24VAC for solenoids, so other than running 2 wires (instead of 3) directly to pulse decoders and on to pulse transmitter for relay into CCUs (cluster control units -- Rainbird hardware) and then onto central PC server, I don't know how that would be any cheaper or more efficient than putting an equivalent Hall sensor on the pipe.
So the only thing I've found on 2-wire reed flow sensors, based on my assumption that is standard for 2-wire flow meters/sensors, you would use a 1K or 10K pull down resistor between black wire (typical), then continue the line into the Arduino I/O signal input pin( 2-13 with Uno). The other (red) wire from pulse sensor would have the 5v line. But pull down resistors can be used on red wire depending on normal-open or normal-close types. Could I use it this way to get a signal into the Arduino board?
2nd question: my pulse-counter/tester works well with seeing output on 2-wire flow sensors and I haven't used it with Hall effect signal wires, so how would you wire up this tester to count raw pulses from the Hall sensors?