Converting The Loop Output To A Scaled Integer Value - Siemens SIMATIC S7 System Manual

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Converting the loop output to a scaled integer value

The loop output is the control variable, such as the throttle setting of the cruise control on an

automobile. The loop output is a normalized, real number value between 0.0 and 1.0. Before

the loop output can be used to drive an analog output, the loop output must be converted to

a 16-bit, scaled integer value. This process is the reverse of converting the PV and SP to a

normalized value. The first step is to convert the loop output to a scaled, real number value

using the formula given below:

The following instruction sequence shows how to scale the loop output:

MOVR VD108, AC0 //Moves the loop output to the accumulator

Next, the scaled, real number value representing the loop output must be converted to a 16-

bit integer. The following instruction sequence shows how to do this conversion:

ROUND AC0, AC0

is the scaled, real number value of the loop output

is the normalized, real number value of the loop output

is 0.0 for unipolar values

is 0.5 for bipolar values

is the maximum possible value minus the minimum possible value

= 27,648 for unipolar values (typical)

= 55,296 for bipolar values (typical)

//Include this statement only if the value is bipolar

55296.0, AC0 //Scales the value in the accumulator

//Converts the real number to a 32-bit integer

//Converts the value to a 16-bit integer

LW0, AQW0 //Writes the value to the analog output

System Manual, V2.3, 07/2017, A5E03822230-AF

S7-200 SMART

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