Control Wave Micro / Bristol file type conversion ?

darkesha · Oct 18, 2021

Any Bristol experts here, or anyone familiar with CWM environment ?

If I convert real into 2 integers in the plc (to N7:0 and N7:1) and send this to RTU, is there a way to convert this back into a floating point (REAL) ?

Can't find anything in Emerson's documentation.

drbitboy · Oct 18, 2021

I assume you have two 16-bit integers and and want to reconstruct the 32-bit real their bit pattern represents.

There is a mathematical approach, using bit-wise ANDs and floating-point DIVides and such, but I would look for ways to COPy the bits into the float, possibly with byte-swapping, to get the answer directly.

What is the make and model of the PLC that has the integers and needs to convert them to floating point?

What language is to be used?

darkesha · Oct 19, 2021

The platform is Bristol line of RTUs - owned by Emerson. Software is Control Wave Micro. Language can be function block or structured text.
I might call their tech support to see if they have pre-canned solution like Schneider has:
https://www.se.com/in/en/faqs/FA243214/

And float would be split into 2 INT at the plc and sent over.

drbitboy · Oct 19, 2021

You want a data UNION in structured text cf. http://www.plctalk.net/qanda/showthread.php?t=119300 or https://help.codesys.com/webapp/_cds_datatype_union;product=codesys;version=3.5.12.0

So you will have summat like

Code:

TYPE ints_union_real:

UNION 
    two_ints : ARRAY[0..1] OF INT;
    one_real : LREAL;
END_UNION
END_TYPE

VAR
    i2r : ints_union_real;
    is_the_val : BOOL;
END_VAR;

[COLOR=blue][B](* replace this with read of one PLC INT into i2r.two_ints[0] *)[/B][/COLOR]

i2r.two_ints[0] := -2048;

[COLOR=blue][B](* replace this with read of other PLC INT into i2r.two_ints[1] *)[/B][/COLOR]

i2r.two_ints[1] := -16513;

[COLOR=Blue][B](* Boolean is_the_val will be true. *)[/B][/COLOR]

is_the_val := (-0.9998779296875 = i2r.ints_union_real.one_real);

It will be straightforward if the byte and word order are the same in the PLC and in the RTU, but you may need to fiddle with byte and word order, but that is the basic idea.

Cf. https://en.wikipedia.org/wiki/Singl...cision_binary_floating-point_format:_binary32

darkesha · Oct 20, 2021

Thanks sir. It might be a good idea to set the test bench and see what is possible.
I do hope ST in CWM allows for much of that syntax.

C McAlpine · Oct 22, 2021

What are you using to send the data? Maybe if you do the conversion in whatever you are using to transfer the data it would remove a layer of complication. I have done a similar task with Red Lion DSPs into a CWM from a PLC 5.

Otherwise as far as my memory serves there isn't a function for that built into the CWM. You could convert both integers into reals in the CWM and do the math to combine them?

Control Wave Micro / Bristol file type conversion ?

darkesha

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