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Entry type: FAQ Entry ID: 39334504, Entry date: 04/01/2016

For an S7-1200/S7-1500 controller in STEP 7 (TIA Portal), how do you scale integer values in real numbers and vice versa for analog inputs and outputs?

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STEP 7 (TIA Portal) provides the option of scaling analog values in the user program.

You can use the SCALE_ X "Scale" and NORM_X "Normalize" converters to scale analog values. These blocks are located in STEP 7 (TIA Portal) in "Instructions" task card under "Basic Instructions" and "Converters". A detailed description of the function and parameterization is available in the STEP 7 Online Help. To obtain the Online Help for a block, mark the block concerned (SCALE_X, for example) and press the "F1" key.

In the following examples it is assumed that the measuring ranges are unipolar. The integer input value is then between 0 and 27648.

The following values are generated by the conversion (for determining temperature via current measurement, for example):

Integer value
(analog value)
Measured value
(in the 0-20mA range)
Measured value
(in the 4-20mA range)
Phys. value

Example 1 - Conversion of an analog value into a physical value (analog input, taking the example of determining temperature)
The upper and lower limits are MAX=27648 and MIN=0 for normalization and MAX=150°C and Min=20°C for scaling. Since the input values are of the Integer data type and the output values are scaled as Real data type, the NORM_X function converts the data type from Integer to Real. The value 20000 corresponds to a measured value of 14.4676mA in the 0-20mA measuring range.

Fig. 1

The connection of the two blocks as in Fig. 1 results in the following definition between the input value of the NORM_X block and the output value of the SCALE_X block:
------------------------------------------- = -----------------------------------------

If the input "VALUE" of the NORM_X block has the value 20000 and the limit values as in Fig. 1, then the output "OUT" of the SCALE_X block has the value:

20000 - 0 SCALE_X_OUT - 20
------------- = -----------------------
27648 - 0 150 - 20

SCALE_X_OUT = 114.04 (corresponds to: 114.04°C)

Example 2 - Conversion of a physical value into an analog value (analog output taking the example of a control output)

Since the input values are of the Real data type and the output values are scaled as Integer data type, the SCALE_X function converts the data type from Real to Integer. The integer value 27648 corresponds to the upper limit and the integer value 0 to the lower limit of the output range. For example, for a control output of 65.0 the analog value 19968 is scaled, which corresponds to a current value of 14.4445mA (in the output range of 0-20mA).

Fig. 2

To change the data type conversion for the blocks, mark the block concerned and click on the yellow arrow. You can then select the required data type conversion from the drop-down list that opens. You must then change the parameters, because the data types of the parameters have changed.

Fig. 3

Additional Keywords
Voltage measurement, Temperature measurement, Resistance measuring, Pressure sensor

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