好吧，附一段程序供大家参考，这是用在S120+增量型编码器，通过读取编码器度数计算移动距离的程序，给这个应用类似。前面的回帖不严谨，再次纠正一下：判断上溢时除了判断增量的绝对值>MaxValue/2,还有判断差值为负。

//==================================================================

//Calculate actual position by r482

//==================================================================

//------------------------------------------------------------------

//Initial

//------------------------------------------------------------------

#MaxPulseVal := 4294967296.0;

//------------------------------------------------------------------

//Read actual value(r482)

//------------------------------------------------------------------

#uData.CurrCycleReadVal := #ActReadVal;

//------------------------------------------------------------------

//Calculate increment value per cycle

//------------------------------------------------------------------

#uData.IncrementVal := UDINT_TO_LREAL(#uData.CurrCycleReadVal) - UDINT_TO_LREAL(#uData.LastCycleReadVal);

#uData.Status1.PulseOverFlow := ABS(#uData.IncrementVal) > #MaxPulseVal / 2.0;

IF #uData.Status1.PulseOverFlow THEN

    IF #uData.IncrementVal > 0.0 THEN               //underflow 

        #uData.EffectIncrementVal := - (#MaxPulseVal - #uData.CurrCycleReadVal + #uData.LastCycleReadVal);

    ELSE                                          //overflow

        #uData.EffectIncrementVal := #MaxPulseVal - #uData.LastCycleReadVal + #uData.CurrCycleReadVal;

    END_IF;

ELSE

    #uData.EffectIncrementVal := #uData.IncrementVal;

END_IF;

#uData.LastCycleReadVal := #uData.CurrCycleReadVal;

//------------------------------------------------------------------

//Calculate pulse increment per cycle

//------------------------------------------------------------------

#uData.ActPulseIncrement := #uData.EffectIncrementVal / (2.0 ** #FineResolution);

#uData.Status1.PulseCountOK := ABS(#uData.ActPulseIncrement) < #MaxPulsePerCycle;

//------------------------------------------------------------------

//Calculate actual position by pulse increment

//------------------------------------------------------------------

IF #Enable THEN

    IF #uData.Status1.PulseCountOK THEN

        #uData.ActPosition := #uData.ActPosition + #uData.ActPulseIncrement * ABS(#Resolution);

    END_IF;

END_IF;

//------------------------------------------------------------------

//Preset

//------------------------------------------------------------------

#uData.Status1.Preseted := (#uData.Control1.Preset AND NOT #uData.Status1.PresetRaiseEdgeSave) OR #ExtPreset;

IF #uData.Status1.Preseted THEN

    #uData.ActPosition := #uData.PresetPosition;

END_IF;

#uData.Status1.PresetRaiseEdgeSave := #uData.Control1.Preset;

#uData.Control1.Preset := false;

//------------------------------------------------------------------

//Out

//------------------------------------------------------------------

#ActPosition := #uData.ActPosition;

//------------------------------------------------------------------

//END

//------------------------------------------------------------------