Siemens SIMATIC S7-1200 Function Manual page 483

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Accuracy of pulse generation

The smaller the pulse generator CYCLE_P is compared to the period duration PER_TM, the

more precise the pulse width modulation is. To achieve sufficiently accurate control, the

following relationship should apply:

CYCLE_P ≤ PER_TM/50

The manipulated value is transformed with a resolution of ≤ 2 % into an impulse.

When calling the controller in the pulse shaper cycle, you must note the following:

Calling the controller in the pulse shaper cycle will cause the process value to be averaged.

As a result, at output PV, different values may be at input PV_IN and PV_PER. If you want to

track the setpoint value, you must save the process value at input parameter PV_IN at the

call times for complete controller processing (QC_ACT = TRUE). For pulse shaper calls

occurring between these times, you must supply the input parameters PV_IN and SP_INT

with the saved process value.

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