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Hi.

I have a V570-57-T20B with V200-18-E1B, EX-A2X, EXL-CAB2000, IO-D16A3-TO16, IO-D16A3-RO16 & IO-DI16. System has been installed and running for approx. 6 months. ( Actually, two identical systems, with a third just being installed now). Yesterday, I was onsite to make some program modifications. I had connected to PLC but not made any changes. Everything was fine, until, right before my eyes the PLC stopped, screen went black with "expansion io error". LED's on EX-A2X indicated that power and comm were ok. The io modules connected to the EX-A2X had flashing run indicators and all I/O indicators were off. I used the visilogic to RESET the PLC and all seemed fine again, except the I/O modules still had flashing RUN LED's and were not functioning. I unplugged the cable from PLC to adapter....no change. The power and comm LED's were both still on. The PLC showed no errors and appeared to be running. Powered off a couple times to reboot....nothing changed. Did a "Initialize and reset" from visilogic....nothing changed. Eventually I swapped the adpter module with another one and everything was back to normal. I will return the EX-A2X for warranty replacement.

My main concern, however, is the fact that the I/O module could be defective or even just unplugged and the PLC did not indicate any error. This could cause catastrophic machine failure should the PLC continue to run without a portion of the I/O functioning.

Any ideas what can I do to make sure the the adapter is connected and functioning? I suppose I could pulse an output from the snap-in I/O to an input from one of the remote I/O and monitor that input. I am hoping for something that doesn't require additional wiring.

Appreciate any thoughts on this.

Dave

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The PLC tripped when the comms failed while the PLC was running, which is the expected behavior. If there is no comms to the EX-A2X when the PLC is powered up, then the PLC will run. This is also the expected behavior and is great for testing purposes. This doesn't present any safety concerns because all the outputs are off.

The problem with mixed I/O on snap-on and EX-A2X I can't help with. This is not something I have done before and wouldn't want to anyway. Sorry I can't be of more help.

Cheers,

Justin

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Hi Dave,

Your distributor already forwarded your question to me. Below is the answer.

If the controller recognize the extension modules on power up, it starts running with them. If, for some reasons (cable disconnected, module burned, pick of electromagnetic noise…), the controller stops immediately and issues message Expansion error. Someone needs to come and reset the controller manually. Usually in this case the person in charge is taking care to check the proper operation of the machine.

If the controller on power up/reset doesn’t recognize the expansion modules, it starts running without them and without any special message. This is done to ease debug/tuning procedure, when quite often the programmer has the controller on his desk without expansion I/O connected.

If there is option, that person in the field will run the controller without expansion modules (which I fully agree with Dave – it can be dangerous!), simple logic can be added, like:

SB2 SB90 Any MB

---| |-----| |------( )---

This “Any MB” then can be used in the application for relevant action – like stop logic and output relevant message.

Your commments are welcome.

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Ah...SB 90...well, SB 90 is actually reserved for specific instances, and isn't for general use, which is why it neither described or documented.

However, in the specific case under discussion we recommend it be used exactly as shown.

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Hi

I have used SB90 for checking the communication link on a number of applications and it works well.

On older versions of VISILOGIC there was a description of what it was for.

Just a suggestion, why not have the expansion i/o error active at all times but have an option in the information mode to switch the PLC to test mode.

In this way the user will always know when there is a problem and the programmer can run in test mode to test the program.

Test mode could also be used to activate some other features such as virtual inputs etc.

Regards

Denis

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Hello all,

I wanted to take this topic up again. I am being asked to make a control system where there is going to be a combustible gas monitor. Whenever that monitor reaches the LEL (Lower Explosive Limit) I will have to use the PLC to shutdown all devices in the area that do not have C1D2 or NEMA 7/9 ratings. This is perfectly fine except that if I put any analog devices on an expansion module such as the combustion gas meter it is a potential problem.

I understand Emil's response earlier in the chain, but in this case there will relatively un-knowing oil field personel that will simply more than likely just reset the power on the PLC. To their eyes everything will look like everything is fine they will never call to notify anyone of the event and from experience whenever you just reset an expansion analog module the PLC simply holds all of the last values it saw the last time the module was connected and then the oil field personel will leave and the system will have stagnant information that will never move and never change causing incorrect process decisions because of bad data.

Im am able to take the steps above to keep the PLC from taking any action, but I would feel much more comfortable if we could at least get a useful explanation of how SB90 works so I can understand the twists and turns of using it in an application where safety is the main concern. Secondarily it sounds like MB90 can be triggered by several things. From a troubleshooting standpoint is the only thing that will fire SB90 durinbg the first scan a lack of connection with the remote IO or if something else can trigger it I need to understand it so I can write a meaningfull users manual for my equipment.

In this case I will just put other analog inputs on the remote IO-ATC8 module other than my LEL monitor, but anything I put on the ATC8 will be non functional until someone with appropriate knowladge arrives to do something about it.

Thanks

Keith

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Couldn't you just store a value (say 0) into all of the MI's linked to the analogue inputs on power up? This way you can detect that the MI's are not being updated.

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That is a reasonable work around to increase safety, but from hundreds of miles away on a phone I would definately prefer a difinative fault reason if SB90 is capable of having a defined reason so that when the call comes in I can just say "Oh yes expansion module communication has been lost". But I like the way you think :)

Thanks

Keith

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Keith

In older version of the help files there was a description for what SB90 is, however I can not remember what it was.

From what I can tell it only goes high if communication is lost between the plc and the EX-A2X.

We use the PLC with snap in and EX-A2X to control large compressor motors and we use a contact of SB90 to do the following.

1. Closed contact of SB90 on the coil of each drive.

2. Open contact of SB90 to display the following message on the screen "Communication failure power down PLC to reset".

Not sure if this helps.

Regards

Denis

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Ah...SB 90...well, SB 90 is actually reserved for specific instances, and isn't for general use, which is why it neither described or documented.

However, in the specific case under discussion we recommend it be used exactly as shown.

Hi

Just a suggestion, why not have the expansion i/o error active at all times but have an option in the information mode to switch the PLC to test mode.

In this way the user will always know when there is a problem and the programmer can run in test mode to test the program.

Test mode could also be used to activate some other features such as virtual inputs etc.

Regards

Denis

I would feel much more comfortable if we could at least get a useful explanation of how SB90 works so I can understand the twists and turns of using it in an application where safety is the main concern. Secondarily it sounds like MB90 can be triggered by several things. From a troubleshooting standpoint is the only thing that will fire SB90 during the first scan a lack of connection with the remote IO or if something else can trigger it I need to understand it so I can write a meaningfull users manual for my equipment.

It seems that there is a mystery about exact functioning of a "secret" SB90 system bit... :ph34r:

Reading this topic I am seriously concerned about a lot applications I've made without thinking of such a problem. I suppose that I just expected that the system itself was to recognize that something is missing from Harware Configuration and safely stop everything in such a situation. Now I am not sure how my system would behave... :wub:

I strongly support the request of providing meaningfull way to control system behaviour in the situations when there is a problem with any expansions, Snap-in, wired, wireless... Why not clearly giving the programmer the way to control it and to decide what would be the best to do if... Suppose that the OPLC always check the presence of everything configured in the HW (a watchdog funcion) and by default stops and turns everything off if the watchdog chain is broken, sets some SBs to show the programmer exactly what's going on, but let him reconfigure the behaviour in such a situation i.e. enable/disble some parts of a watchdog chain and probably write emergency subroutines that would be triggered and executed under such a condition. Nice, isn't it? And safe too.

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