Just run it to an osciliscope if you have access to one. It'd be real easy to see the freq. of the AC signal.
It makes sense its an AC signal, they do that to reduce the effects of interference. we did that on some industrial machinery i was wiring over the summer.
If you have questions, jast ask me. I'm a senior Electrical Engineer at RPI, so I could probably help you out.
Greg
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