I’m planning to add INDUCTIVE PROXIMITY SENSOR to my printer, mine has 4mm aluminum bed and 0.03" PEI sheet on it.
Will it work through PEI sheet ?
Yes
I have the exact same setup on my printer! 4mm aluminum with 0.03" pei on top. It works, but in my case the sensor has to be pretty close to the surface of the pei sheet for it to detect the aluminum underneath. So just make sure that there isn’t any hard plastic on your nozzle when you start auto tramming. Btw have you had success with the pei using abs? I haven’t seen any difference compared to similar materials. I still get warping and the corners still lift. Any suggestions?
@Ryan_Branch Thank you for reply,
Regarding ABS printing on PEI, I’m very satisfied as a whole. Sometimes I had little corner lift, but it has gone after I re-adjust nozzle height.
Heat bed temperature is 90 ~ 95 degree and somtimes use brim option.
Ok thanks. Yeah I have ended up using the brim option a couple times, and that seems like the most reliable way to keep it from lifting. I might adjust the first layer height as well. One thing I noticed is that when I attached the pei to the aluminum using some high temp 3m tape, the pei was higher by 0.1mm on one side of the aluminum than on the other. This isn’t a problem unless you are auto-tramming. Since the induction sensor measures the aluminum and not the top surface, you may find that your first layer height is thicker on one side and thinner on another side of the bed. It’s not too big of a problem for me, but something to take into account.
@Ryan_Branch Most of cases, you should print ABS without brim option 
I use brim in case of first layer is somewhat like thin lines or very small area, for safety.
Anyway, good luck!
Did you prepare the PEI sheet any particular way? I just attached it to the aluminum. I haven’t done anything else to it, like sanding it.
@Ryan_Branch No, I purchase it from Amazon toghether with 486mp tape, just taped it.
Actually, I ruined it yesterday once by using acetone for cleaning purpose. I sanded out surface to come back. It worked.
@Ryan_Branch Did you detach very thin vinyl on PEI before tape it?
Yeah, I removed the vinyl.