Intermittant Pausing

I will post my real problem: during normal runs, our plc seems to hault all operations to our pullers (in a pultrusion machine). It would pause at various lengths of time (typically a few seconds and sometimes longer) and would resume on its own. The intervals that this would happen are random. Since this would be fatal to our pull, we are desparately looking for a solution. This unit was already programmed and functioning when we acquired this machine. Unfortunately, documents and interface supplements were not included, therefore, I have no way of getting into this toshiba EX-20 PLC. Has anyone had any similar problems??

Thanks.

P.s. When this PlC pauses, the outputs to hault operation are on. The inputs from the sensors seems to be all off at this moment. Almost as if the program has shut everything off for some reason.

If all your inputs are going off at the same time like you say I would check the commons for my inputs for problems. The PLC might be hanging because it is losing the signals from the inputs.

here again...

nothing personal, here, Henry. You sound like a guy like the
rest of us, trying to get through a shift.

Lets examine the facts of this case:
1.)..."be fatal to our pull, we are desparately looking for a solution."

SOLUTION: Bring in a highly skilled professional, let him observe the machine, and replace the EX-20 as soon as possible. Pick ANYTHING that you already use in your plant. With no feature I can think of, the EX-20 is completely replaceable with anything currently on the market, and the I/O is not that extensive that it will take long to do.
WHY: Your think your present symptom is that you can't see the EX20 program, and thereby effect a fix. This is not a symptom, this is a PROBLEM. Fix the PLC problem, and all the rest of it goes away.

2.)..."documents and interface supplements were not included"

SOLUTION: See above. Note, make sure that Mr. Skilled Professional knows going in that you will demand that he reveal all passwords, schematics, etc. that you pay him to generate.
WHY: Fool me once, shame on you. Fool me twice, shame on me. The real cause is that somebody somewhere in your organization skipped some steps a bit of time ago. They likely saved a lot of money then, but, guess what.... the party's over. Time to sober up.

Lastly, you're not alone. I have a customer in the aluminum extrusion business with one puller that supplies his entire plant. He has no listing, no disks, no software... NO CLUE. I quoted a project whereby I replace the obsolete controller and he has at least some life left in his plant. Rejected. why: too expensive.
On the positive note, I have another (real) customer that recently asked me to change over PLCx and replace it with PLCy. Total change over time: 15 minutes. In this case, his system would 'hang up' every so often, just like yours, but, A: the parts for PLCx could only be had on eBay, and B: he had no desire to invest in hardware and software to support a 15 year old piece of hardware. (sound familiar). This guy is now paying attention to other things in his plant, and the hang ups on this piece of gear and simply a watter-cooler story from the past.

You have choices.
A: Do nothing, keep scratching you head, and HOPE for the thing to get better by itself.
B: Follow a plan from start, through the middle, towards the end. Define all the phases of the project, and get on with more important things in life.

P.S. I'm not trolling for flames here.

Well said, Jeff...

I doubt that's what Henry wants to hear, but he should take this current problem as a reminder that this controller needs to be replaced.

Henry, since you have NO documentation, we are pretty much as 'in the dark' as you. Greg's suggestion is certainly a possibility, as well as a zillion other things it could be.

Another 'guess' I'll throw out there is a sensor somewhere that's not turning on (or off). The program could simply be waiting for this input in order to continue. Eventually the sensor turns on (or off), and the process continues as normal. Finding it will be the difficult part...

Good luck!

beerchug

-Eric

Came accross a similar one where a sensor was shorting 24V power to ground.
The supply setup for the sensors only put our either 50 or 100mA (I can't remember which) and was separate to the output supply. A dead short was not enough to trip the circuit breaker, but would pull all the inputs low.
Tracked it down to broken insulation on the sensor cable, bare copper occasionally shorting on a section of the machine where the paint had been scraped off.
9:30 at night to 12:00 midnight.
Not too bad.....

This was on an SEW VF drive with IPOS, so not quite a PLC.
This was controlled by a drum controller originally installed around 1965 and still going strong. The VF drive was a later modification.
No PLC on board.

Doug

Doesnt the thing have an HMI ?
If not, then it is certainly lacking a key component of any non-trivial control system.
I dont miss the time when there was only lamps and pushbuttons.

If the there IS an HMI, then the programmer forgot to add alarms and messages for the operator to tell him what is going on.

It does look like the machine is waiting for one or more inputs.
If ALL inputs are off, then you should hunt a common supply or ground potential.

After all the pulling, while the PLC pauses (rests) does it have an encapsulated smoke ???

For ecapsulated smoke explanation see this thread.
Encapsulated Smoke

Jesper
I wish you would talk to my consultant engineers. Just building a control board now. 95 switches, pushbuttons and lights on the damn thing. Buying plenty of PLC gear.

I think I found a picture of Bob's control panel...

[attachment]
beerchug

-Eric

The main advantage of old-style mimic screens are that they can be made large and clear to see from a distance.
They can even be "beautiful".

But the disadvantages are many:
- Extra IO in the PLC for the lamps and buttons.
- Cost and time to wire the whole thing.
- Making changes "afterwards" is a nightmare (and the larger the project, and the longer it must "live", the greater the risk that modifications will be needed).
- How about alarms ? A lamp for each alarm, or a socalled alarm annunciator. Extra work, extra expenses.

A modern HMI panel avoids the disadvantages and adds bonuses:
+ Alarms and events will be logged.
+ Need more HMI's ? Just put a couple more where you need it at just the cost for the panel (the application is the same, so no expense there).
+ Trends.
+ Huge savings in cost if you can reuse HMI code between projects.
+ Can tie neatly into the PLC code if done properly. Makes software maintenance a lot easier.

One important note: The most frequently used functions should still be activated via switches/pushbuttons.

edit: I forgot to mention the possibility to update PLC and HMI remotely. This is a major bonus for OEMs.

Oooohhhh!!!! A demo board Eric. Not far wrong though. Hard to find room for the labels.

As you know, my preference is Omron. Have used Compo Bus S (Omron's prorietary version of Device Net) on the back of the doors. Helps lots. Very few wires to doors. Costs a bit more but cuts the time by heaps.