Signal range of data type real

Hi

I have two questions.

I have had a problem reading REAL numbers through ModBus and always get the sem error [-5] in the MBTCPRead block. Does anyone know what this error stands for because it is not in the manual? When I swich over to read DINT I have no problems.

I'm trying to read from ABB ANR96 Measuring station and since I'm not able to read REAL I wanted to read the 64bit INT and convert to REAL but then I found out I could not write value higher than 2147483147 (MaxDInt). Why can I not write higher value in REAL variable that I thought was in IEEE-754 format that should have maximum representable IEEE 754 floating-point value (2 − 2^ (-23) ) × 2^ (127) ≈ 3.402823 × 10^ (38) ?

Thanks for quick answers,
Danath

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Danath Rank: 2587

Asked 11 months ago

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As I know, you can't read dirctly REAL trough Modbus. Modbus supports only 16-bits transfer - e.g. INT or WORD.

Error -5 means that you used the wrong data format for read variables, set at MBTCPRead block (for example WORD). You have to use only INT or DINT for these parameters.

I'm reading the 32-bit real trough Modbus by means of 2 consequent INT variables, then use 2 blocks INT_TO_WORD and then WORDS_TO_REAL (using correct big endian format).

Respectively DINT_TO_WORD or DINT_TO_REAL have some disadvantages - please look in CBM help for this.

In order to read 64-bit real by means of Modbus, you can look in the post

http://www402.abbext.com/How-read-64bit-modbus-data-AC800M-controller-Mass-Flow
-Meter-q6294709.aspx

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by Danath Rank: 2587 on 9/14/2017 1:41:19 AM | Like (0) | Report

If I read the real values they are 32bit so I can use your solution that looks to be a decent one.
But that brings me to question 2, what is the biggest number I can have on 32bit real in 800xA system since I get "Bad value" if I try to write value higher than 2147483147. Have you tried to write value higher than this in the 32bit real variable in 800xA system?

by kstoilov AKS expert

Rank: 8 on 9/14/2017 1:55:09 AM | Like (0) | Report

Don't understand the question - you have 2pcs 16-bit int, read trough modbus. Then WORDS_TO_REAL take care for representing of the real value. I think in this case at the output of WORDS_TO_REAL you can receive higher than 2147483147 because that is a limit for DINT (input), and not to the REAL (output).
Pay attention - you can't write higher than 2147483147 at each input DINT ! But that should be handled by your slave device ANR96 - it should divide the real into 2 consequent dint
Please try

by kstoilov AKS expert

Rank: 8 on 9/14/2017 1:57:17 AM | Like (0) | Report

The output of the DINT_TO_REAL) should be defined as REAL in 800xA

by Danath Rank: 2587 on 9/14/2017 3:45:21 AM | Like (0) | Report

My second question has nothing to do with modbus. It is internal 800xA problem.
-open up CBM
-Open Control Module editor
-create new variable of type REAL
-Try to set initial value higher than 2147483647 with out getting "Bad value" error when you compile (Check).

by kstoilov AKS expert

Rank: 8 on 9/14/2017 5:37:07 AM | Like (1) | Report

see answer below

by Danath Rank: 2587 on 9/14/2017 11:23:13 AM | Like (0) | Report

Your solution works perfectly, thanks

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kstoilov

Rank: 8

Answered 11 months ago

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That is another beer.

In CBM Editor, in case you put initial value for real variable, you have to put a decimal point ! Especially if the value is greater than 2147483147

For example:

A/ 214748314722 (bigger than 2147483147) = report Error 1040 : Variables : Bad number: 214748314722

B/ 214748314722.0 = no error

As principle, it is a good idea the real values to be written as real number -> 1.0 instead of 1

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kstoilov

Rank: 8

Answered 11 months ago

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Signal range of data type real

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