The use of the limit instruction I posted will not move the speed to zero if the number is out of range. It will do nothing. As the rung will be false, no change will occur it will just stay put at whatever value is there.
But do whatever you are comfortable with.
I see; so, there's no need to change the program further because being out of range will simply leave it in the last commanded speed - Excellent. Again, your help is greatly appreciated.