when using a Sick retro reflex sensor to detect product in trays entering a Fuji flow wrapper, the sensor sees a small gap in the product spacing, and the machine faults on insufficient gap. Is there any way to prevent a sensor giving a double blip?
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Yes. The most common way of doing this it with a delay-off timer in the PLC. You can also get time delay relays, which might be easier if you don't have access to the PLC code. I quickly found a multi-function timer relay available from an online distributor for under $40. (Note that I am in the US; other places in the world may have wildly different pricing and availability.) Sometimes, it can be as simple as angling the photo-eye a little bit, so that it doesn't look straight through gaps. Of course, that won't work if you need high repeatability in sensing the leading edge.
Sage Automation, Inc.