Thermocouple not Reading in Siemens PLC

[Tweeker]

I am operating a Siemens IM151-8 F Processor with 4 6ES7-134-4NB01-0AB0 2 channel thermocouple cards. I am getting no reading from any of the inputs with or without a reference selected.

Has anyone experienced this before?

 

[JesperMP]

Are the channels assigned inside or outside the process image ?
Are you reading the values as IW or PIW words ?

 

[Tweeker]

Thanks for responding Jesper. I am new to Siemens Plc's.

What do you mean by channels assigned inside or outside the process image? I set up all the thermocouple i\o in the configuration.

I am attempting to read the data through IW words. Is that not correct? What are PIW words?

 

[L D[AR2P#0.0]]

What address have you used?

 

[JesperMP]

The process image is the IO address area that is automatically updated by the CPU.
Analog inputs are usually placed outside the process image, and if you just let STEP7 assign the address it will chose the address outside the process image.
On most S7-300 PLCs the default process image size is 256 bytes inputs and 256 bytes outputs. So from 0-255 the addresses are inside the process image, from 256 and higher they are outside the process image. The size of the process image can actually be adjusted in the hardware configuration.

To read or write addresses outside the process image you have to use "P" for direct Peripherial access. I.e. PIW256 instead of IW256, or PQW300 instead of QW300.

edit: If you are using TIA to program the IM151-8, then the syntax is %IW256 when you want to read an address with direct peripherial access.

 

[Tweeker]

Thank you for that explanation Jesper! That is probably my issue. I am using Portal V16 to program this cpu and I did let the configuration set the addresses. I was looking directly at the %IWnnnn expecting data and didn't see any.

I will try accessing the data as peripheral and let you know what happens.

Again, thanks.

 

[Tweeker]

Ok, so I went back to verify the process image was large enough that the input word fell within that range and it does. So now I am back to square one. I do not seem to have any data from all four of my thermocouple cards.

Would safety modules in my system be an issue?

 

[JesperMP]

Would safety modules in my system be an issue?

No, should not have any influence on the TC inputs.
It is a 6ES7134-4JD00-0AB0 card ?
I dont have experience with this.
The hardware configuration is loaded on the CPU ?
Do you have any hardware diagnostic errors ?
If you enable group diagnostics for the card, and wire break detection on each channel, do you get some more diagnostic information ?

 

[JesperMP]

You need to have a power module before the TC modules, and the power module must be supplied with 24V, do you have that ?
(I would guess you would have module errors if the power was missing).

 

[JesperMP]

And just to be sure, you have selected the correct type of TC for each channel, not 'deactivated' ?

 

[Tweeker]

To answer the questions above, the card is configured correctly. Other engineers have verified this for me. Attached is a picture of the system I am working with.

 

[Tweeker]

The digital input cards are working fine. None of the thermocouple cards nor the RTD module are giving me any data.

 

[JesperMP]

Both TC and RTD cards dont have data !

To answer the questions above, the card is configured correctly. Other engineers have verified this for me.

You know what they say, trust is good but ....
Post a screenshot of the parameter setup of one of the channels for each type of cards.

 

[Tweeker]

 

[JesperMP]

It looks fine except for on the TC card, channel 1 is deactivated but it looks as if all TC channels are wired up in the photo. But channel 0 should provide some data so it does not explain your problem.

I use IM151-8 and ET200S with STEP7 Classic, not TIA.
If you go online with the CPU, does it show all modules as "ok", i.e. it shows a green tick mark box at each module ?