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Good evening

I am trying to use a timer to let me know when a carton running down the belt is too long.

I know the exact speed I am running and the length the carton should be, therefore I know how long the timer should be set for

I have a photo eye to detect the start of the box.

This is what I assumed would happen

If the photo eye is made for too long I would get the TD timer to be true, therefore if it was true I could make a bit and ah ha there was my proof it was too long.

Tried this, didnt work

anyone have any thoughts?

Thanks

 

 

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I had the identical application a few years back...  I used the photoeye to see the beginning of the carton, and an encoder to count pulses generated by the conveyor movement.  I had to use the encoder because the carton size differences were very slight.  This worked great even if the conveyor speed changed.

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Flex

Hit it the nail on the head.... my photocell had a bad connection

as soon as I fixed that, it worked like a dream

Thanks guys

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That solution brings to mind a story - years ago I had a bottle counting problem with a polarized retro-reflective photoeye and the customer swore there was something wrong with my program.  I bought one of those little USB oscilloscopes (wanted one anyway; just needed an excuse) and it pointed out that the neck of the bottle was occasionally causing a tiny double pulse.  In that case we had to re-position the eye, but the problem was uncovered.

 

I still keep it in my car and get it out to help solve mystery input problems caused by drive noise or inductive flyback pulses coming off contactors.  It is a great troubleshooting tool.

 

 

Joe T.

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https://www.linkinstruments.com/oscilloscope.html

 

These guys are in New Jersey and have been good to work with.  They actually design these things.  I blew mine up once by connecting the probe ground lead to what I thought was a grounded heat sink (actual voltage - 60V).  The thing I didn't realize was the ground on the probe is not isolated from the ground on the USB plug, which is grounded through the computer when you have your battery charger plugged in.  I blew up that USB port, too.  Anyway, I called them and they had me send it in for repair - the bill was $75.

 

I have the older brother of the MSO-9201.  Not cheap, but I love my tools and I've spent more money on more useless stuff (like Allen Bradley Tech Connect contracts).   It does spectrum analysis, too, which is really good for looking at drive harmonics and then showing the customer how they match up to noise on DC PLC inputs because they were either stupid or too cheap and ran their motor wires in the same conduit as their signal wires.  Invest in a 100:1 probe if you want to go there.  The maximum input of the included 10:1 probes is 500V peak.

 

I can tell you that my street cred with the customer increases by an order of magnitude when I get this thing out and show detailed pictures of their signals.  Once again - the inductive flyback pulse is the most dramatic.  I've seen it induce spikes across traces on a V200-19-E1B and cause a PLC's watchdog timer to kick out.

 

Joe T.

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