Timed permissive ?

Snap25

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Join Date
Dec 2014
Location
Michigan
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On one of our conveyors we have a height verification sensor that is triggered by a photo eye as product passes by. QA wants another sensor to take snapshot of the temperature as well. Due to a lack of places to mount the sensor I had to put it 10 inch’s diwn the line and using a separate sensor to grab the anal value in the plc.

If the first validation check fails, I want to pass on that particular item on the second sensor. I don’t want to log 2 failed products if 1 item fails both validation points.

As product fails the first check, it’s very likely that a passed item is going through the second check point and possibly another item inbetween the too points.


As is, is my best option to time up when to ignore check B if check A fails?
 
I would set up an array to capture the first test and as the items pass the second sensor for testing remove it from the array. It would be a FIFO setup in the plc. Using timing can cause a number of other issues if there is any difference in spacing of the product on the belt or the belt changes speed for any reason. It is always a better idea to find other ways to handle the situation.
 
Is it possible to use something like a barcode scanner or RFID to uniquely identify each part? Then the usual track and trace stuff kicks in where you can have an array, and record each pass/fail for each part in a big array.
 
On one of our conveyors we have a height verification sensor that is triggered by a photo eye as product passes by. QA wants another sensor to take snapshot of the temperature as well. Due to a lack of places to mount the sensor I had to put it 10 inch’s diwn the line and using a separate sensor to grab the anal value in the plc.

If the first validation check fails, I want to pass on that particular item on the second sensor. I don’t want to log 2 failed products if 1 item fails both validation points.

As product fails the first check, it’s very likely that a passed item is going through the second check point and possibly another item inbetween the too points.

As is, is my best option to time up when to ignore check B if check A fails?

You could use a bit shift and load a "1" at the first position if height is okay and a "0" if it isn't. Run the bit shift on a timed pulse only if the conveyor is moving. If you get a "0" at the second position, then ignore the temperature reading.
 
Thanks for the suggestion. I'm going to try a few file/shift instructions in an emulator tonight.
 
+1 for the Bit Shift. It's easy to understand, and Bubba won't call you at 2am because it doesn't work.

Bubba.
 
I agree. I've been using it in my emulator, seems pretty basic.

Eventually, they are going to add a rejection system as well. If Check A passes and sends a 0 down the array, is there a way to have Check B place a 1 in the array? Or do set up two separate cascading arrays?
 
Last edited:

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