1756-if8 1756-IF8 rev 1.5 Input tags freeze

4 posts in this topic

This is a 1756-IF8 rev 1.5 Analog Input module.

This has happened a couple times where the Module Input Data, (not mapped), goes to the high limit and freezes (Data Monitor data is static).  Plant operators pointed out the trending wasn't accurate.

There is no fault on the module, no yellow triangle on the system tree for the module.  The Module properties show no faults, and RUNNING.

I have done a "Reset Module" both times, (Module Properties - Module Info tab), while monitoring the module data.  As soon as it resets, instantly the Data Monitor starts showing live data.

I'm going to try and replace the module at first, but I have some concerns.

  1. Has anyone run into this before?
  2. I can't seem to find any information on the "Reset Module" animation, and what it actually does.  Any information, (or where to look), would be appreciated.
  3. I don't like to hot swap, but I believe I will need to in this case, (utility).  Will the current properties, e.g. scaling transfer to the new module?


Dave Redman

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Dave - 1756-IF8 is a multi-channel module, I would check for a single channel fault which will show up in the Data Structure not the I/O Tree.

Reset Module usually does a "cold reboot" of the module just as if it was turned on.

As to "hot Swapping" - one of the claims to fame of the ControlLogix Family is that modules are proported to be "hot swappable".

That said since this is an analog card the skeptic in me would suggest the following procedure:

1. Remove the Terminal Strip from the Module. No unwiring should be required.

2. Remove the Old Module

3. Install the New Module

4. Reconnect the terminal strip.

This means that all the in card op amps will have power before the i/o signals are added to the card.

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Good information, everything makes sense.

Also on Tech Connect chat.I was informed that ground noise might also contribute to this issue.

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@der0492 Thanks for sharing the Tech note because though we're always on the lookout for EMI, I didn't know that was a possible anomaly for the IF8. And we use quite a few of them.

To add to @BobLfoot's comments, when you have to hotswap, (Allen Bradley calls it RIUP, for Removal and Insert Under Power) I'm a big fan of placing the controller in the program mode, if possible. If the process is dependent on these inputs for control, and you remove the card in the run mode...... well, use your imagination, lol. Bad things could happen to your process.

In any case, the card's configuration is held in the controller and written to the new card so yes, all your scaling, etc, will immediately be written to the new I/O card when it powers up. But there's a catch or two:

  • The new card must be a direct replacement card for the one coming out.
  • If the "Electronic Keying" setting in the card's properties is the default "Compatible", the firmware on the new card must be the same or higher than what's saved in the controller.
  • If the keying is set to "Exact Match", the firmware and everything else on the new card must match exactly what the old card was.

Hope this helps, even though you hopefully were able to locate and remove an EMI issue and not have to replace parts. Let us know how it goes, please.

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