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Check for quality information [message #1803146]

Sat, 23 February 2019 15:34

Philipp Ziegler

Messages: 4
Registered: February 2019

Junior Member

Hi,
I have less experience with 4diac-IDE and want to know someting about
a check function for structured text. Is there a possibility to check an input
of a basic function block whether it has no value. This could be for example
a subscribe-block has no value and outputs "not a number".
My question in structured text could be as follows:

bool_check_nan := FUNCTION_CHECK(Output_of_Subscribe_block);

Is there any possibility to access such a function?

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Re: Check for quality information [message #1803260 is a reply to message #1803146]

Mon, 25 February 2019 22:14

Alois Zoitl

Messages: 1582
Registered: January 2014

Senior Member

Hi,

unfortunately such a functionality does not exist. I would say currently I don't see a way to even provide such a functionality. But this comes from the data type system from IEC 61131-3, which defines that there is always valid data in a data type (maybe except for real and lreal).

I think the only option you have is that you have a dedicated Boolean value informing you about the validity of your data. You could even expand that to a time value giving you the freshness of the data. This could be rather easily be provided by an special communication layer.

To reduce the number of connections you could put this together into a struct. However structs are not so nicely usable yet in 4diac.

I hope this helps you.

Alois

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Re: Check for quality information [message #1803264 is a reply to message #1803260]

Mon, 25 February 2019 23:48

Alois Zoitl

Messages: 1582
Registered: January 2014

Senior Member

I just noticed that I forgot to mention the most important means IEC 61499 has to offer for you: events. A subscribe block which has never received any data, has never triggered an IND event. You can use this event to either set a Boolean (e.g., E_SR) or you trigger your FB based on the IND event. This allows you to build even more interesting applications as the means I described in my last post.

For example you can use different states in your FB for when no values have been received and when you have values. This shows much more explicit the behavior of your FB.

[Updated on: Tue, 26 February 2019 08:41]

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