21 posts in this topic

I have a problem with PLC not seeing the input. I am using a FX3S, however, because I still am using GX Developer, it will only recognise it as a FX1N. My problem is I did a small programme for an alarm on a "Blow Down" system for filter cleaning on Silos. Tested it at home with a cyclic timer, everything working fine. Got the controller this afternoon and found I had a problem. It looks like it's not seeing the input to reset the time out timer. Worked for a while, then fell over. Using X0. The switching time I am monitoring is 20msec, which I thought would not be a problem. This is going to be a major setback for me with this project. Eight of these controllers. Any help would be great.

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FX3 is extremely reliable, so I doubt that it is hardware failure. You could post your program so we can analyzer situation. 

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Download a simple program to test the hardware, something like X0 = Y0.

If this works ok then it is your program, Like Goran said - can you post your program?

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Thanks for the reply guys. Forgot to say I can see the X0 input led coming on with every pulse. I didn't have my laptop with me at work on Friday, so couldn't debug it on the controller. I will attach the programme I have written for it, really simple, so confused where it's falling over. Hopefully you can spot the stupid mistake I'm making.643a7300eed8c_PLCCode.thumb.jpg.5ac8b076

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Hi Asad,

Thanks for the info on GX-Works2. I don't understand how to reset the timer after a cycle. What I don't get, it worked fine for hours at home, then when I put it in the unit at work, it stopped working. That's what confuses me.

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How long is the input X0 on for, during normal operation?
Have you connected the S/S terminal correctly for Sink or Source input connections?

Edited by Moggie

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According to the specs on the controller, it's 20ms. I have it connected correctly. I have brought both PLC's home and running them again all day. No problem at all. I even thought that the pulse from the controller might not peak at 24 Volts DC, so I tried it a little while ago with 12 Volts DC, still works every time. I am using a cyclic timer, so I can't say exactly the duration of the pulse I am putting on it at home, but it's really quick, works every time. I have downloaded GX-Works 2, have reinstalled it on both PLC's, so they are recognised as FX3S units. I'm at a loss. I will try them tomorrow again and will install GX-Works2 on my laptop at work and see what the hell is going on. It's a simple programme, so I can.t see scan time being a problem. Even if it misses half the pulses it will still work. The S/S is definitely connected correctly. 0 volts and X0 +24V. What bothers me it did work when I first put the PLC in the controller. I'm grasping at straws now.

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One thing to consider is the time between X0 turning on.
If the delay between operations of X0 turning on is less than your T0 Timer value then the timer would never time out.
(as it restarts every time X0 (M1) turns on and then off)

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That's exactly what I want. I only need T0 to time out if there are no pulses. Than Y0 turns off and the alarm in my Loading Panel is activated and I close the inlet valve.

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Note:  I blocked Asad.  The website he (repeated) linked was redistributing Mitsubishi software via Google drive, possibly maliciously modified.

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What is your input pulse interval? Normal condition, the input will always pulsing? If abnormal input no pulse?

During actual test, does Y0 trigger?

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I'm really at a loss now. Had it on test all day at home yesterday with a cyclic timer, perfect. Put it back in the controller today, same thing. The input will work at times, and then nor. Y0 does turn on when X0 sets M0. What I don't' understand, when I look at the programme "Online Monitor". I actually see X0 go blue, but doesn't pulse M1. What is that about. However, because the time is K2400, it does hold up for a while, however, M1 doesn't reset the time all the time, only now and again. I give up!

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Are you using the same PLC at home as at work (with exact same program)?

What creates the pulse on the input X0 at work?

If from a seperate system make sure the 0V is common to both.

Edited by Moggie

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Been really busy with other things. However, this problem is still stopping progress with the project. Same PLC that I had on test at home. I will post a picture of the unit I am trying to get the alarm working. There is 4 solenoids that pulse to clean filters on silos, I am using the 5th output as an input to the PLC. They are 24 Volt DC outputs to the coils. The 0 Volts is common to the whole lot. According to the specs of the unit, the pulse should be 20msec. I can't verify that. Any help would be great!

Controller.jpg

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So its a reverse jet cleaning system.

There may not be enough "load" on the PLC input for the 5th solenoid output to operate correctly OR the pulse is too short.

Can you not use the relay alarm contacts??

 

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They do not alarm for the reason I'm looking for. They are mostly for differential pressure alarm etc. All I want is when the unit fails. The chap that adapted them for me advised the only way to get what I wanted was the route I'm trying. Not sure what I'm going to do.

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It sounds more like a load problem on the 5th output not allowing it to operate correctly!

Can you connect a temporary load to it as well as to your PLC input to test?

(You may need to connect a "free wheel" diode across the load as well)

Or an oscilloscope on the 5th output to see the time of the pulse?

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Hi Moggie, I have since connected X0, X1, X2 and X3 to the four valves. It works after a fashion, it will see a pulse now and again, but it's not reliable enough to put into service. I do not have an oscilloscope, however, one of the contractors on site has said he will bring one in tomorrow for me to check the length of the pulse. However, I'm sure it's a bit too quick for the PLC to read. What would be the minimum in msec's that would work? According to the manual, it appears 10 msec seems to be the minimum. I have to come up with some solution. I'm looking at trying to get a Weidemuller  MCZ TO 24V/150MS MODULE. It will see a minimum of a 3.5 msec pulse and hold the output for 150 msecs. Just might have a problem with availability. Projects can be problematic most of the time.

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Okay, I really give up now. Tried a freewheeling diode, no change. The manufacturer gave me access to the unit. I have to take the pulses up to 1 second before the PLC responds, which is useless. Minimum I can go is 120msesonds, no chance of the PLC even seeing that. I really give up now. Going to Plan B.

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31 minutes ago, Richard Webb said:

Okay, I really give up now. Tried a freewheeling diode, no change. The manufacturer gave me access to the unit. I have to take the pulses up to 1 second before the PLC responds, which is useless. Minimum I can go is 120msesonds, no chance of the PLC even seeing that. I really give up now. Going to Plan B.

So it is a timing issue.
You could try the "Pulse Catch" function see image.

Pulse Catch.PNG

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Hi Moggie, thanks for all your help, I have sorted it. The pulse from the board was a strange one, got it switching a solid state relay and SSR to X0, all fine now. Thanks again.

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