Red Lion HMI not reading correctly a PLC tag.

Hello all,
I'm working on a project using an AB CompactLogix PLC and 2 Red Lion HMIs (G3) running Crimson 3.0.
The PLC and the HMIs are connected to an Ethernet switch, this way establishing all the communications through Ethernet.
The HMIs run identical version of the same project, both reading from and writing to the (same) PLC.
Something weird is happening with a tag on the HMI that reads the running status of a motor controlled by the PLC. I can see this tag ON in the PLC program, but on the HMI screen is OFF almost all the time. Once every 5-8 seconds it turns to ON for less than a second and then goes back to OFF. I tried with some other tags associated with the same motor, and with the running status of other motors, and they were retrieving the expected values from the PLC.

Any clue about what could be happening?

Thank you!

Hello,

I have no idea with the Red Lion but from a general troubleshooting viewpoint the symptoms described lead to:

#1 The tag referenced in the HMI is not correct. Maybe a case difference or a bit offset.
#2 A memory overwrite in the PLC but because of PLC scan time to HMI scan time the toggling of the memory is not seen as frequently as it is really occurring.
#3 Something in the HMI is writing to the tag locally but not the PLC.
#4 Some systems can be configured to set the state of a tag when a communication failure occurs. Maybe it is failing, for that tag, and only once in a while is valid and that is when it is true.

All monitoring programs, HMI, PLC debugger etc. are not, normally, in-sync with the PLC scan.

Put a one-shot and a counter on the memory location in the PLC. See if it is toggling and the HMI is not seeing it because of scan times.

If the counter is not incrementing that leads to the HMI. Now it gets fun.


Good luck,

Mark
http://www.peakhmi.com/

Elcan,

As in your other thread I would recommend having the second HMI communicate through the first so you don't have two masters talking to the PLC.
Also you might be looking at a possible addressing issue with the button. What version of Crimson are you running and what communications driver are you using?

Thanks
Jeremy

Jeremy,
This issue disappear without any action from my part.
I'm using Crimson 3, build 222.

I don't know how to implement your recommendation. Could you refer me to a section in the Manual, or any tech note that can guide me through this?

Thanks!

Elcan,

If it is working than I wouldn't worry about changing anything.

My recommendation is to leave one HMI as is, then instead of configuring the second HMI to talk to the PLC it would talk to the first HMI. The first HMI would have one of its other Ethernet protocols configured for Modbus slave and you can use gateway blocks to expose its registers. Then the second HMI would be configured for Modbus master and would talk to the first HMI.
If this is not clear feel free to give me a call and I can explain it over the phone.
800-677-7880

Thanks
Jeremy