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krome
July 23rd, 2009, 07:51 PM
i have a npn prox sensor to detect metal i want to mount it next to a reel to know when it stop moving so i was looking to put some kind of material over the reel to cover some of it up to just leave a couple of metal showing. does anyone know what could work? i try carboard and it didnt work

thanks

Sergei Troizky
July 23rd, 2009, 08:20 PM
:) This is impossible.

krome
July 23rd, 2009, 08:22 PM
why u say that

keithkyll
July 23rd, 2009, 08:39 PM
A proximity sensor detects metal. Cardboard won't block the magnetic field. You should use a photoelectric sensor with a reflective piece of tape on the reel.
Is this a permanently mounted reel? You could add a screw to the reel. then position the detector so it senses the screw head. Use one with a fairly flat head for best results. In the PLC, run a timer and use the prox on it's reset input. When the timer times out, the reel has stopped.
Do a second timer to do the same thing in case the reel stops exactly on top of the sensor. For this one, the prox feeds the enable input.

krome
July 23rd, 2009, 08:42 PM
thanks but i got to use this sensor im thinking the sensor need to be 5mm close to the metal so im thinking of putting a plastic tub that is thick on it and adding some metel like a screw made work thanks for that idea

leitmotif
July 23rd, 2009, 08:56 PM
thanks but i got to use this sensor im thinking the sensor need to be 5mm close to the metal so im thinking of putting a plastic tub that is thick on it and adding some metel like a screw made work thanks for that idea

Why just stopped? You can talk about the sensor all day BUT you need to consider where the sensed signal is going to and what you are going to do when it gets there. Tell us about the whole system.

If you are really wanting to sense when the reel is stopped a prox may work but a zero rpm switch may be more appropriate.

Dan Bentler

krome
July 23rd, 2009, 09:00 PM
im using the prox sensor to be use as a event counter that is counting the time that see the reel turn then if it doesnt detect the reel turn it will send a discrete signal to a relay that will turn off a valve. the counter is working in HZ so if it doesnt see it at least 2 twice it will consider it as not moving.

plc noob
July 23rd, 2009, 09:46 PM
Another solution http://www.hubbell-gleason.com/preeng/LimitSwitches/Series55.pdf

keithkyll
July 23rd, 2009, 09:48 PM
Another way to do it is drill a hole in the reel and sense when the prox is off. This works when you use a 4mm prox and can mount it within 2mm. With an 8mm prox, the hole needs to be a good size, over 1/4 inch diameter.