Thermocouple not Reading in Siemens PLC

[Tweeker]

 

[Lare]

Do you have right terminal module (base) for TC and also for other AI cards?
https://adegis.com/media/asset/1dcad01f3bd0a8e35c4c478c701f3dc6e07263a6471a29699b75a6a82b5dcb46.pdf

 

[danw]

The ckonfiguration is for a 4-wire thermal resistor, presumably the RTD, but the photo of the RTD in post 11 appears to show a 3-wire, 2 red wires and one white wire, with a white wire jumper connected somewhere the photo doesn’t show. Is there no 3-wire selection that avoids a jumper?

 

[Tweeker]

Do you have right terminal module (base) for TC and also for other AI cards?
https://adegis.com/media/asset/1dcad01f3bd0a8e35c4c478c701f3dc6e07263a6471a29699b75a6a82b5dcb46.pdf

Yes, I have the correct bases for the modules.

 

[Lare]

Yes, I have the correct bases for the modules.

Another one could be that you have selected more recent firmware version for than cards actually has.

 

[RVaughan]

Please send a screenshot of the I/O address area of the module's properties. There are a few dropdown menus below the address assignment where you may select which Process Image Partition the cards are associated with.
Have you tried addressing them with %IWnnn?

 

[Rob...]

Looking at the wiring, are you using proper thermocouple cable? Looks to be normal copper wires, which of course will not give you readings.

As a test, you can get a small length of thermocouple cable, wire into the cars, at the other end, strip the wires and twist together, you should have a reading of around room temperature.

 

[Tweeker]

Actually, I upgraded the firmware to the latest from the Siemens website because of this issue. I will try taking the firmware to a lower version.

 

[JesperMP]

Rob.. mentioned something pertinent about your wiring.
Care to comment on that ?

 

[Tweeker]

This panel is an old panel I am using to learn about Siemens PLCs. All of the connections to the TC cards are run to terminal blocks (not my design). I have tried wiring the two thermocouples I have to the terminal blocks AND directly to the TC cards. Always the same result of zeros on the input address.

 

[Tweeker]

Another one could be that you have selected more recent firmware version for than cards actually has.

Reduced the firmware version of the processor from 3.5 to 2.7. Still have the same result.

There is no option to change the firmware of the TC cards.

 

[Tweeker]

Please send a screenshot of the I/O address area of the module's properties. There are a few dropdown menus below the address assignment where you may select which Process Image Partition the cards are associated with.
Have you tried addressing them with %IWnnn?

This was mentioned earlier from JesperMP and I thought I checked it. Apparently, I verified it incorrectly because the addressing was the issue.

Thank you for your help.

 

[Tweeker]

Ok, now how do I access that data outside the process image to for display on the HMI? I cannot create a tag with the address of %IWnnnn.

Thanks.

 

[RVaughan]

Ok, now how do I access that data outside the process image to for display on the HMI? I cannot create a tag with the address of %IWnnnn.

Thanks.

In the PLC program, create a DB or M tag and MOVE %IWnnnn to that tag.
Create an HMI tag that connects to your new tag.

 

[Rob...]

IW256 and IW256 will display the same value....

Only IW256 is updated asynchronously.

256 is an example address, not sure what yours should be.