Analog Inputs and Outputs in an S7 PLC are represented in the PLC as a 16-bit integer. Over the nominal span of the analog input or output, the value of this integer will range between - 27648 and +27648. However, it is easier to use the analog values if they are scaled to the same units and ranges as the process being controlled. This applications tip describes methods for scaling analog values to and from engineering units.
The program for scaling analog values consists of 2 function (FC) blocks. These blocks are optimized for unipolar (0..27648) analog values, but will also work with bipolar analogs. Both blocks are shown in two different languages: LAD and STL.
The program for scaling analog values consists of 2 function (FC) blocks. These blocks are optimized for unipolar (0..27648) analog values, but will also work with bipolar analogs. Both blocks are shown in two different languages: LAD and STL.
FC100 converts an integer in a nominal 0..27648 range to a floating point number in the specified engineering units. FC101 converts a floating point number in the specified engineering units to an integer in 0..27648 range.
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