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2 cells on the same input automation

Crousti_9257 Posted messages 13 Status Member -  
jeannets Posted messages 28397 Registration date   Status Contributor Last intervention   -

Hello,

I am new to industrial maintenance and I need to add a sensor to a machine to stop a conveyor of butter pots in case of a blockage. Let me explain: there is already a sensor wired to the Omron PLC that stops the conveyor if the pots pile up and cut the beam of the sensor. Now, I need to add a second sensor that should perform the same action as the first, and they are both wired to the same input of the PLC. However, the issue is that the beams of both sensors need to be interrupted to stop the conveyor because even if one of the two sensors detects a pot, the other continues to send 24V to the PLC. So, I would like a solution to stop the conveyor when either of the two sensors detects a pot.

Thank you

8 answers

  1.
    jeannets Posted messages 28397 Registration date   Status Contributor Last intervention   Ambassadeur 6 603
     

    Hello,

    It's an "OR" condition, so it's one or the other, on an input OR of the automaton, to be inserted into the already existing program.

    You can also connect your cells in series... One after the other, and change nothing in the program... So both "contacts" will normally be closed; if one opens, the carpet stops.

    When both beams are interrupted, it does not remove anything from the conditions met; on the contrary, it confirms them.

    Or did I misunderstand..??

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    1. Crousti_9257 Posted messages 13 Status Member
       

      In fact, when there was only one sensor connected, the conveyor stopped if it detected an object for more than 3 seconds. Now that there are two sensors connected, both sensors must detect an object for 3 seconds to stop the conveyor. However, what I want is for the conveyor to stop if at least one of the two sensors detects an object.

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  2. mariam-j Posted messages 47 Registration date   Status Member Last intervention   39
     

    Hello,

    You need to connect your two cells to the inputs of a door: "NAND" and the output of the nand to the input of the automaton.

    And of course, power the nand with 5 Volts.

    However, if both cells detect at the same time --> 0 at the output.

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    1. Crousti_9257 Posted messages 13 Status Member
       

      OK, I'll check that on the machine tomorrow, thanks.

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  3. billi
     

    Hello

    I don't understand everything, but if the current is cut off when an object passes in front, you connect them in series. For now, you have connected them in parallel.

    The 24v goes through the first one and only comes out if there is no object in front; you send it to the second one that you install, it only comes out if there is no object in front, and you send it to the conveyor where the first one was previously connected.

    Both sensors must not have an object in front for the current to finally reach the conveyor that runs.

    If only one has an object in front, the 24v current won't reach the conveyor, which stops.

    You should be able to modify the connections without remaking all the harnesses, just at the point where both sensors take the 24v, only one should take it, the other sends it back to the conveyor, and the output of the first one is connected to the input of the second one without entering the control box.

    Come back and tell me if it works, and if it's okay, let me know what a conveyor is.

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    1. Crousti_9257 Posted messages 13 Status Member
       

      No, actually the sensor sends 24V continuously to the controller as long as there are no pots in front. As soon as the beam is interrupted, the 24V is no longer sent to the controller and the conveyor stops. However, now with the two sensors, even if one of them detects and stops sending 24V to the controller, the conveyor does not stop because the second sensor continues to send 24V since it does not detect anything.

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      1. mariam-j Posted messages 47 Registration date   Status Member Last intervention   39 > Crousti_9257 Posted messages 13 Status Member
         

        It is not the cell that sends the 24 V, it is the controller.

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      2. Crousti_9257 Posted messages 13 Status Member > mariam-j Posted messages 47 Registration date   Status Member Last intervention  
         

        On the sensor, there is power and the contact. I thought that since the sensor is powered by 24V, it would send the 24V back to the controller via its contact only when it does not detect.

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      3. billi > Crousti_9257 Posted messages 13 Status Member
         

        Hello

        Sorry. If each sensor always sends 24v but it needs to be checked with a multimeter and there are 2 independent inputs in the programmer and you have gates that you program, I would tend to say that you need to connect each sensor to the input of an "and" gate so that the output only powers the conveyor if 24v is present on both sensors at the same time (no failure in sight). As soon as one sensor is cut off, there is a failure somewhere, so the output cuts off the conveyor.

        The only thing I don't know is how the "and" gate works; if no sensor is sending 24v, you need to verify that the output also cuts off the conveyor when there is a failure at both locations. (and I don't know if your gates can directly handle 24v).

        There would only be one conveyor command at the programmer's output, but still 2 distinct sensor inputs at the programmer's input.

        Not a bad idea; if the current is cut off on one sensor, it can no longer see the failures, it cuts off the conveyor for safety.

        In this case, would the 3 seconds already be programmed at the level of each sensor? It's up to you to decide on the operation.

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  4. mariam-j Posted messages 47 Registration date   Status Member Last intervention   39
     

    To make it work with both cells at the same time, you need to add an "AND" gate in parallel to the NAND.

    The two cells on the four inputs two by two and the "NAND" and "AND" outputs together.

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    1. Crousti_9257 Posted messages 13 Status Member
       

      Okay, I'll try and let you know.

      Thank you for your help.

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  6. jeannets Posted messages 28397 Registration date   Status Contributor Last intervention   Ambassadeur 6 603
     

    Here is my montage of the double cell

    It's quite simple, origin: cell 1 connected to the controller... on A and B

    Then, addition of cell 2, connected to cell 1 in series and wire B' is connected to the controller taking the place of wire B in full.

    These two cells are "normally closed contacts"... they become open in case of obstacles in front of the cells...

    They use a single port on the controller, the same one...

    A cut wire will thus be detected.

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  7. billi
     

    Hello Jeannets

    This is what I was thinking when I said to put the cells in series.

    (But maybe it couldn't be done if the cells need to be constantly powered at 24v and if they need to be monitored independently by the programmer? Some cells really look like independent devices after all and not just a simple contact, if at startup it starts by opening and initializing, it's more complicated to manage for cell 2 in your drawing because if it needs to let through a few pots and count 3 seconds locally, but not take the time to initialize? It is still dependent on what happens in cell zone 1. Does that interfere or not?)

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  8. Crousti_9257 Posted messages 13 Status Member
     

    Hello,

    Thank you all for your responses.

    My boss just told me this morning that we won't be touching the program of the automate, so I thought of a solution and came up with this (see attachment).

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  9. jeannets Posted messages 28397 Registration date   Status Contributor Last intervention   Ambassadeur 6 603
     

    It is not always easy to know, without being able to visualize and experiment.

    -- These cells must be compatible Omron modules... they have a brand, a model, and a technical data sheet or Datasheet... here, we have none of that, we imagine the principle based on experiences already had... but it remains a bit in the fog, it may also require adjustments...

    Usually, these modules remain powered (24v) regardless of the state of the signal coming out of them... it is either a 24mA current loop or a dry contact...

    Your drawing seems good in this hypothetical situation... imagined, but it’s up to you to be on the field and carry out the action...

    You can help yourself with a mock-up created "on the table" before moving to the real thing.

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