This same question was asked recently.

[Most likely] Answer:

If you are looking at the watch table, the values only change once you enable live monitoring.

Click the green arrow.

If they are not changing now, create a new watch table and add the tags to monitor one at a time while the green arrow is checked.

Engineer_Athens

Hello everyone, 

I'm using a S7-1200 PLC for my PhD experiments. I have connected some thermocouples, 2 flowmeters and a pyranometer on it .

For the last two (flowmeters, pyranometers) , I have written the needed blocks so as to translate the pulses to lt/min (flowmeter) and the voltage to Wm^-2 (pyranometer). When I monitor the block values the results are the expected ones (especially for the pyranometer). However, when I monitor the corresponding tag values in the tag values table, the results are not the same as in the block monitoring. In specific, the tag values referring to the pyranometer and the flowmeters are stuck and do not change. Why does this happen?

I'm quite new in the field of PLCs, so any help would be appreciated.

Regards 

Engineer_Athens

I'm quite new in the field of PLCs, so any help would be appreciated.

Posting a screen capture of your problem,
would go a very long way to understand you clearly.

_{1 x picture >= 1000 x words}

You are programming Siemens like Modicon or some other PLC manufacturer.

Siemens is share memory with byte callouts.

Examples:

MB2 is byte at memory location 2

MW2 is a word starting at location 2, and ending at memory location 3

MW3 is a word starting at location 3, and ending at location 4 in memory

MD2 is a double word starting at byte 2, ending at byte 5

MD3 is a DWord starting at byte 3, ending at byte 6

If you look at your picture, you are using MD2 and MD3 for related by not the same value, so they are overlapping each other.

If you are manually assigning tag references, please stop.  Assign a name, and allow Portal to provide the next unused chunk of memory available for that datatype.

It will likely do something like MD2 and MD6 rather than MD2 and MD3.

If you have similar memory overlapping in your project, you need to fix it.

A simple way to do it is to delete every tag from your tag table that has the potential to overlap.  Then compile and use the errors to quickly go to each undefined tag, right click on the tag, define it and accept whatever reference portal chooses.

Recompile and try again.

Engineer_Athens

Thank you guys for the responses.

Hereby follows a screenshot of the block and the tag value. 

Can the difference be explained somehow?