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stanwich

photo eye latch

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Hello everyone! Could someone give me a little direction? Im sure its a little basic, Im trying to replace a limit switch with a photo eye. basically i need a piece of lumber to pass the photo eye then it will stop at a j hook. when the line is clear the j hook will drop long enough for the lumber to pass (timer needed) . The limit switch worked well because the length of the wand allowed the input to stay on, The photo eye needs to be able to latch on because the lumber passes it then travels a little to the hook ,. basically small peices of lumber dont cover the photo eye . Should i be using a [ons] before my latch?, any discussion on this would be great.

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Could you use Emitter- receiver or Photo eye- Reflector combination? If they are positioned diagonally across the lumber path with one where the limit switch was and the other close to the hook position that should give you functionality similar to a limit switch with a wand.

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Use an off-delay timer. The output of an off-delay timer will come on as soon as the PE senses the object, and then will stay on for a preset time after the object clears the sensor. Then you use the output of the timer to drive your hook, instead of the sensor input. Due to your mention of a ONS instruction, I'm going to hazard that you're probably using an Allen-Bradley PLC, in which case your off-delay timer is a TOF instruction. If you're not sure how to use it, drop one in, click on it and press F1. The help file is very, er, helpful.

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thanks for advice, im already using a tof for the output , what i ended up using was just a latch turned on by the p/e then unlatched by the timer .dn, The latch will tell the plc something is there even if the photo eye isnt blocked and i wont have to worry about the timer timing out if the machine stops.

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No problem, yep that's about the way I would have done it. Glad you got it working!

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