Ladder program on Mitsubishi-type GFX3 PLC turns on LEDs but not contacts

Discussion in 'Programmer's Corner' started by quique123, Oct 25, 2018.

  1. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    OK I'm at a point where I'd like to just pay someone to clear everything up for me.

    I understood that you had to match your inputs (like sensors etc) to your PLC type. This makes sense because if a sensor is sourcing type (pnp), it means that we connect V+ to the sensor (brown) and Vo to a sinking type plc such that current flows from PS to sensor and down to PLC Gnd or 0V, hence sinking.

    Also if the sensor is npn them the v+ goes to the plc first, then the plc sources the current to the sensor which sinks the current to 0V.

    In this case the plc is stated as a sink type plc in the documents.
    4F2C4B9F-0AB4-4559-8BB5-849A1F56AFBE.jpeg
    This means the sensor would HAVE to be Sourcing or PNP, but I had to use a sinking Npn sensor. So is the manual WRONG?

    I tried asking the manufacturer this and they replied with
    5C6557F1-5444-42CC-846A-73CE7779B4F4.jpeg

    which is confusing. So Scott comes in and fixes the pnp wiring which is wrong because it was wired for 48V. But then his pnp wiring in Post 71 is exactly the same as what the manufacturer sent for npn which I posted in 70.

    Then post 74 confuses me completely because I think Scott is saying that's how to wire an npn input to an npn plc (which is not supposed to be possible) and the diagram shows current flow in different directions in the same wire. Then in Post 78 Scott adds that indeed you cannot connect an npn with an npn!

    Throw my slowness to grasp new things into the mix and I'm desperate. So what do I have in the end:

    1. A theory that says that I can't connect an npn input to an npn plc.

    2. An npn plc that apparently only works with npn inputs! .

    3. A wiring diagram from the manufacturer corrected by Scott which seems to show an npn connection and a pnp connection which are identical.

    4. And my lingering confusion as to how it all works and a plc that apparently has a SS terminal that must be jumped to 24V in order to work, instead of being able to use the plc as either sink or source the way that SS terminal is supposed to make it work.
     
  2. ScottWang

    Moderator

    Aug 23, 2012
    6,373
    987
    The Sourcing type (as PNP) of PLC connected to the Sinking type (NPN) of sensor, the +24V connected to the +24V power supply of PLC.

    4F2C4B9F-0AB4-4559-8BB5-849A1F56AFBE_quique123_ScottWang.png
     
  3. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    Ok thanks Scott. I understand your image, I think. So I just have to understand that I have an npn sensor with a plc that accepts npn-sensors because maybe its actually a pnp plc, that needs a 24V-to-S/S jumper in order to work.

    I can live with that.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    6,373
    987
    The circuit below was that I mentioned in my posted #78, to adds (in series) a stage PNP circuit between the PLC Sinking (as NPN) type and the Sensor Sinking (NPN) type, the 20K limited the Ib current of 2N3906 to provide less 1.2 mA, so it may allow Ic to sourcing less than 12 mA, that is according to the draw current of PLC sinking, Rbe 6.8K was related with the turn off frequency of 2N3906, different frequency has different values, 20K are the same.

    PLC sinking type to sensor sinking type_Improved_quique123_ScottWang.png
     
  5. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    Yikes

    Well so the manufacturer was wrong in saying their plc is a sinking type?
     
    Last edited: Nov 4, 2018
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Not sure who you have been communicating with but I have previously contacted Chinese factory support for clarification on their products and in some cases the answers I have had back have been very poor and contradictory, I got the impression it was not the engineering dept or tech support but the marketing dept. and really not completely knowledgeable in their product.
    The only way in this case is to find out, or get help, in finding out empirically what the configuration actually is.
    In the right hands, it should take no more than 10-15mins.
    Max.
     
  7. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    Yeah that's what I'm leaning towards.

    Well thanks so much for all your help. If youre ever in Honduras let me know :)
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I will,
    At one point in time I almost made a move to the other (British) Honduras, now Belize of course.;)
    Max.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
    6,373
    987
  10. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    Thanks Scott. I'm confused enough as it is so I'll skip over that for now until I understand my plc better. Thanks for all the help.

    Great Mac! Let me know! Or I can send you some coffee if you're a coffee drinker
     
  11. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    Well this is the end of the demo I'm trying to set up so here is the final issue. I thought I had it figured out but I ran into a hiccup.

    I'm trying to add the solenoid to complete the project. The motor runs and moves objects along a motorized band and when they reach the sensor a solenoid actuated a cylinder and pushes the piece into a bin.

    This is how I wired it but the solenoid doesn't activate even though the output it's wired to (in the Plc) does light up.

    I believe it to be a common connection issue since I have a 12v power supply for the motor and a 24v power supply for the plc/sensor. However, since I connected the solenoid to 24v psu because it's a 24v solenoid, I'm connecting it's ground to the Y01 output which uses Com0 which is connected to the other (12v) psu's (-).

    Would that be the issue or is it cometh ing else completely? Sorry I'm asking without trying but I don't want to burn my solenoid like I did my sensor

    BA02C8D5-A5D2-4678-8D25-E87877F277E4_quique123-02.jpg
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You should be able to the 24v for the solenoid different 0v commons connected to the COM0 terminal should not matter, as long as +24v is connected to the solenoid, the other terminal of the solenoid connect to the output Y01.
    Max.
     
  13. quique123

    Thread Starter Member

    May 15, 2015
    161
    3
    Sorry, on the solenoid 1 & 2 are connected, not 1 & GND; 1 is connected to 24V and 2 is connected to Y01.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Ensure the solenoid current is within the output rating of the PLC.
    Wire a reverse (BEMF) biased diode across it, 1n4002 etc.
    Max.
     
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