How would I go about doing this?
Generally speaking, there are two ways you could accomplish this.
One way would be to place a tag on the cap and a small reader module on the tank. When the cap was open, the tag would be out of the read zone; a low-frequency (LF) or high-frequency (HF) system would work well for this application, since you could easily control the read field. Another might be to create a circuit that would close when the cap was closed. The circuit would be connected to the RFID chip's input/output ports. When the cap and circuit were closed, the chip would detect that to be the case and pass that information along to the host system, via a reader.
The former solution would require a battery-powered reader, and that battery would need to be changed. You would also need a skilled systems integrator. The latter solution might involve some custom engineering work, but it should not be too difficult. Systems that employ the open/closed circuit technique are presently on the market. I hope that helps.
—Mark Roberti, Founder and Editor, RFID Journal
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