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Can anybody Help


i'm a student just starting to use the V570, 

and i have just a quick question


Can you set an MB to output a mA output to a control valve?


the set up consists of a pressure transducer which inputs a 0.25 - 4 volt input to the plc, then i wish to convert this input to produce an output of 4-20mA which operates a control valve.


I also have a maintenance screen which i want to operate the control valve  independently to the input.( i.e. press a button on the h.m.i and open the valve 25%,50%,75% and 100%) is this possible. Picture attached below.




dylan( S.I.S==Stressed Irish Student   :wacko: ).


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Dear Stressed Irish Student,

The direct answer to your question is no. You cannot set and MB (digital output) to set an analog output.

However, you can use the Linearization FB to make this conversion. 

The first problem you have is a non-standard input device (0.25-4 V), but this can be solved by using only a fracture of the 0-10V input value. Then you need to scale this value to fit a 4-20 mA value. I attached an application that demonstrates this.

Inside the linearization FB you will find 6 values. These value depend on the resolution of the I/O module (in our case it is 10bit, what means that the values range is 0-1023): X and Y are the input and output respectively. X1 is the minimum input value, and because the minimum input value is 0.25V, our X1 value will be 1024/10*0.25=~26. Y1 is the minimum output value (which is 4mA) and will be calculated as 1024/20*4~=204. Respectively, X2=1024/10*4=410 and Y2=1023.

That's it. Now you have a signal convertor.

Regarding you second question, you can add a term for Auto/Manual mode and manually set the output value.

See attached application and help file regarding analog I/O definitions. For more information see Visilogic help.

V570_Analog converter.vlp

Analog IO.pdf

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