I know nothing about PLC-CX3G except for some of the videos ive been studying about using melsoft GXWorks2 for programming the PLC I have. I have gotten it to light up 4 leds on the plc in sequence, Y0, Y1, Y2 and Y3 with timers that count 5 seconds and turn on the next led, and then the leds turn off again in reverse sequence. But the thing is that I thought that meant that the actual output terminal or contact (not sure what the proper name is) would also be sourcing current/voltage from them. But when I put the voltmeter at each terminal (when its led is lit obviously) and the other lead to GND, I get no voltage.

Is it something in the program that differentiantes LEDs from actualy terminal outputs that Im missing? I come from an arduino background where whenever you set pin 13 high for example, the LED on pin 13 lights up and there is also a 5V potential across that pin and GND. So Im confused as to why it doesnt work the same in the PLC.

 

Physical Outputs are Yxxx the nature of which can be relay, or S.S., source or sinking depending on the model etc, if the output is on and you read nothing, then it is most likely sinking output if you do not read a voltage.
You need to check details on the model you are using.
Max.

 

Thanks and what exactly does that sink mean? Iow, what would I need to do if that is the case?

 

This explains the different I/O, you would need to check the particular PLC you are using to confirm the nature of the output.
https://library.automationdirect.com/sinking-sourcing-concepts/
Max.

 

Also the primary outputs are Transistor (sink or source), Triac, and relay contact closure.
Max.

 

Thanks. I found on the plc documents that it is RT, so mixed Relay & Transistor types. But I can't find any info on sourcing or sinking.

OK so I sort of understand sourcing and sinking. I guess my experience with arduino had only exposed me to sourcing types?

So I'm trying to wire a dc motor. So that means I need to wire a dc motor so in this case it shouldn't matter right?

 

The link I posted shows sink or source outputs clearly, the load is either in the positive or the negative side of the supply.
For e.g. a relay contact can be made either way.
Ensure the DC motor does not exceed the current rating of the output.
Max.

 

So like this?

I'm using a 24v source so I'm using a divider for the 12v motor:


I just read in the docs that the relay output index and transistor outputs of the plc that COM is connected to the negative terminal of NPN; does this mean it's sinking?

The link I posted shows sink or source outputs clearly, the load is either in the positive or the negative side of the supply.
For e.g. a relay contact can be made either way.
Ensure the DC motor does not exceed the current rating of the output.
Max.

 

I just read in the docs that the relay output index and transistor outputs of the plc that COM is connected to the negative terminal of NPN; does this mean it's sinking?

Yes.
Max.

 

Yes.
Max.

OK I'm trying to wire it up now and if I understood your link correctly this is the one:


Now what I'm confused about is that I have:
1. 0V terminal on my plc, next to the 24V in. This is connected to the psu's - terminal.
2. Gnd terminal on my plc.
3. COM terminal on my plc.

So when the diagram says the Common connects from plc to - of the psu:

A. Do I connect Com on my plc to the psu's - terminal? That would be the same as connecting to my plc's 0V but would that be the same as GND on the Plc?

 

I am familiar with the GFX3 apparently the CFX3 is a Mitsubishi knock off, the Mitsubishi I am pretty sure has output depending on model version, IOW comes with Relay, Sink Transistor or Source transistor according to order suffix.
With the FX family of Mitsubishi you have a S/S (sink/source) terminal that can either be connected to the 24vdc supply or the 24v common in order to select either sink or source.
Max.

 

I think in my case COM is not Common, there are 3 of them and they read Com0, Com1 and Com2. According to the Use Manual they are communication ports?

Never mind, the com port refers to the RS232 and mini-usb. I was looking at the first page, far right, near the mid-bottom.

Ok so I would definitely need COM0 because it seems to be the common port to the outputs Y00-Y03, and my output is Y003. So Ill connect it to the - terminal of the PSU.

 

Yes the COM terminals are for the sink point of the output so this would be PS common and +ve P.S. would feed the load.
Max.

 

Ok and just out of curiosity, what is the difference between COM and GND?

 

Ok great, I got it working. The motor does move kind of slow, not sure why, ill have to look into that, but it works. I guess I should also add that diode. Now Im moving onto the sensors.

 

Without looking at the spec's, I would guess it is the Earth GND terminal.
Jumper the output to COM and see if it speeds up, (output cause?).
Max.

 

Ok the results of jumpering Y03 & COM:
The motor runs when I jump them, it runs at the same speed, so it might be a PS amperage issue.

As for the sensor, Im working with a PNP Capacitance Prox Sensor (LJ3...), Ive got the wiring figured out:


But as for the PS, I probably shouldn't use the same PS that Im using for the motor, right? So I might want to get a PS just for sensors?

As for the Sensor's COMmon terminal should I use the same one as for the motor as well? This is what it looks like, sorry for the coloring, I didnt use colored wires.

 

Using the same commons should not matter, but I would use a separate supply for the motor, can you use the PS for the PLC for the sensor?
Max.

 

Yes, the PLC-PS is 24V and the sensor is 3-36VDC

 

OK the sensor doesn't work, maybe I wired it wrong.

Here is the program:


And the wiring is:


When I pass an object in front of the sensor y1 doesn't light up. I moved the sensor brown wire to the plc ps (+) terminal. The blue is connected to the Com0 and to the plc ps (-) and black is connected to x0. This is a pnp sensor.