Hello. I am honored to present my present work committed in 15 minutes during the performance of works at the end of the world, i.e. in Central Poland. Needed was a flow meter with pulse output to control the chemistry dosing pump. Of course, there are ready-made flow meters / water meters with such a function, only that within a radius of 30km, they are not immediately available. The system had a built-in water meter with a mechanical counter, and a reed switch sensor at the pneumatic cylinder position, a small neodymium magnet and a cyanoacrylate adhesive. After disassembling the measuring system, I made a notch in the measuring disk 1dm? / revolution and I put in them a magnet with dimensions of 2x3x3mm. I attached the reed switch to the lid and it was ready:
No revelation. If you did it without opening the meter and put it on a sealed counter it would be a feat.
And since you have a meter unsealed, it was necessary between the overlay and the mechanism to insert the HALL sensor there is already a magnet that carries information from the mechanical part (hermetically sealed) for the counting part (plastic "kulak").
On the one hand, the great applause for creativity, most automata can unfortunately only think about learned schemes. On the other hand, a machine part was not available on the market. So it's not removable in the event of a failure.
The system was not used for billing, so removing the seal was not a problem. By the way, it turned out that in newer water meters there is an insert made of some sintered powder around the magnetic clutch, shielding in the event of attempting to block the water meter with an external magnetic field. The dosing pumps have an input on the NO contacts, so the reed switch has the advantage over the hallotron that it does not need power. I could have even less interference in the water meter and mount on it a small reflective sensor (it was at hand) that would work with a counter-painted water meter (3/4 black matte, 1/4 mirror), but it would require pulling a 10m 24V power supply from the neighboring the room, where there is a boiler control cabinet with a power supply, and adding a relay to control the pump. The customer was, of course, informed about the application of such a solution and agreed to it. In the event of failure, replace the commercially available water meter with reed switch.
Hehe. The supplier well known to me, actually one of the most interesting sensor sources at good prices. Only 100km one way. In addition, as I have already written, a primitive water meter with no-reed contacts is enough to control the dosing pump. Price approx. PLN 100. It's just that the topic was urgent, and on this spill they are not in any shop within a radius of 30km, and go to Łódź or Wawy me not calculated (fuel cost comparable to the cost of a water meter, I will not mention the time).