之前看到过的一个随机数的样例，可以给你参考一下：

//Set "No current job" status

#error := false;

#statusID := #ERROR_IN_THIS_BLOCK;

#status := #NO_CURRENT_JOBS;

//Check if the maximal Value is less than the minimal value

IF (#minValue > #maxValue) THEN

    #error := true;

    #statusID := #ERROR_IN_THIS_BLOCK;

    #status := #MAX_LESS_MIN;

    #LGF_RandomReal := 0;

    RETURN;

END_IF;

//Read system time

#tempTimeStatus := RD_SYS_T(#tempTime);

IF (#tempTimeStatus <> 0) THEN

    #error := true;

    #statusID := #ERROR_RD_SYS_T;

    #status := INT_TO_WORD(#tempTimeStatus);

    #LGF_RandomReal := 0;

    RETURN;

END_IF;

//Callculate a random-start-value depending on the time

#tempRandomValue.%B3 := #tempTime.NANOSECOND.%B0;

#tempRandomValue.%B2 := #tempTime.NANOSECOND.%B1;

#tempRandomValue.%B1 := #tempTime.NANOSECOND.%B2;

#tempRandomValue.%B0 := #tempTime.NANOSECOND.%B3;

//adapt the calculated random number to the given number span

#tempNormReal := NORM_X(MIN := #MIN_UDINT, VALUE := #tempRandomValue, MAX := #MAX_UDINT);

#LGF_RandomReal := SCALE_X(MIN := #minValue, VALUE := #tempNormReal, MAX := #maxValue);

"DB_分期".随机数 := #LGF_RandomReal;

#status := #NO_ERROR;