The device you require is called a 'Light Curtain'.
Several manufacturers have them. I have used keyence, but the ones I've seen are all simply presence detectors.
Banner's A-GAGE will suit your application, but you'll need two at right angles to do the cartesian plane function.
Mike O
That's right. 4..20mA has several things going for it over a voltage signal.
1. You can power an instrument directly using a two-wire loop. (Loop-powered instruments)
2. Because of the 'live' zero, cable breaks and instrument faults can be detected fairly easily.
3. 4..20mA is great for...