S7-1500 channel diagnostics (i.e. wire break)

I'm trying to update my analog input FC to also have proper channel diagnostics.
So I enabled all those options for analog inputs on AI cards.
Now, when I go online I can see what I'm getting as diagnostic (wire break when we disconnect AI).

Now I try to get that in my program, for alarms and such.
But it seems it's impossible to extract such data with GET_DIAG function I planned to use. With that I can get diagnostics for remote IO head and I can get diagnostics for module (8x analog inputs card). But not possible to get it to channel level.
I've seen Siemens suggests using interrupt OB (OB82) and RALRM function, but it's not how I like it and doesn't fit our current FC we used in 300/400 PLCs.

So is there a way to incorporate this in FC which is called every cycle?
Is there a number from AI(I've seen 32767 appearing for 4-20mA sensors when they are disconnected) which tells it's wire break? Since that could also be signal overflow (max. value reached).

4..20 mA corresponds with 0..27648 in the program.


We have a custom scaling block, we use <-3456 or >31104 to indicate wire break/overflow.


I think it is possible to extract the channel from the diagnostics, but in case of multiple errors you run into some issues. From what I remember.

boneless said:

4..20 mA corresponds with 0..27648 in the program.


We have a custom scaling block, we use <-3456 or >31104 to indicate wire break/overflow.


I think it is possible to extract the channel from the diagnostics, but in case of multiple errors you run into some issues. From what I remember.

Click to expand...

I think solution here could be simply to declare 32767 as wire break and therefore as channel fault.
Since we use only unipolar 4-20mA in this project I can't test bipolar sensors so I don't know if -32768 is seen when you have wire break for bipolar sensor or it's also 32767 for bipolar sensors.

I'd like to differentiate between field fault (sensor has problems) and channel problems (wire break), because it would save time to know where to look.
Why can we see this in online diagnostics and cannot access it in user program I can't understand, most of stuff you can see in TIA Portal is also reachable from user program. Why would something common like this be so convoluted to extract?

Some devices intentionally give out for example 0 mA or 22mA in case of failure. I have also seen -32768 with wirebreak.


The way we do it catches all (at least most) cases.

boneless said:

Some devices intentionally give out for example 0 mA or 22mA in case of failure. I have also seen -32768 with wirebreak.

The way we do it catches all (at least most) cases.

Click to expand...

Yeah, I think my AI gives me 32767 because I enabled wire break (signals below 1.185 mA, default value offered by hw config). I have to test tomorrow or later what happens when we go 0-20mA range, if I'm correct then when we're below 4mA we should start sliding to negative numbers and then there should be jump to 32767 when value goes below 1.185mA.


I also enabled checks for underflows and overflows (Siemens defined underflow is <-4865 and overflow is >32512), common mode error (don't know how to simulate this to see what I get in this case) and no supply voltage L+.


I guess all this could cause signals to show 32767.