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I've built a setup where I've placed a reed switch near the water meter in my house. Every 0.5 litre the switch gets triggered and my Raspberry Pi does the rest of the work.

My gas meter also outputs a magnetic field. So I've also placed a reed switch on it but it never gets triggered. I've tested with a magnet and the reed switch is not broken. I can "see" the magnetic field when gas flows through the meter and I keep my smartphone with an app to view the field near it.

The producer of the gas meter does sell a product to do the same thing I want to achieve so it should be possible. But why buy a ready made thing if I can do it much cheaper :).

Might I just need a more sensitive reed switch and if so how can I judge which one I need? The specifics of the switch which I'm using can be found here: http://www.produktinfo.conrad.com/datenblaetter/500000-524999/506957-da-01-en-REEDSENSOR_MS_313_3.pdf

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    \$\begingroup\$ It might be better to switch to a Hall-effect sensor for that one. \$\endgroup\$ – Dave Tweed Apr 2 '16 at 21:50
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    \$\begingroup\$ How do you know the gas meter has magnetic output? Are you sure it's not designed for an optical sensor? Photo? Link to datasheet? \$\endgroup\$ – Transistor Apr 2 '16 at 22:24
  • \$\begingroup\$ Eventually I want a low power battery operated system. A reed contact is better than hall effect. \$\endgroup\$ – BennyM Apr 5 '16 at 19:16
  • \$\begingroup\$ It has a magnetic output, it's noted on the meter itself. Mentioned in the documentation and I can see a small fluctuation when using a smartphone app which shows magnetism. \$\endgroup\$ – BennyM Apr 5 '16 at 19:17
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The most sensitive reed switch I see is about 10 AT, which is significantly more sensitive than your switch's 10-20 Ampere-Turn rating.

You might also be able to use steel sheet to guide the magnetic field to the ends of the switch. You might find this Masters thesis useful. Or just get some steel sheet and some snips and play around with it.

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  • \$\begingroup\$ How is 10 more sensitive than 10-20? \$\endgroup\$ – BennyM Apr 3 '16 at 11:13

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