Ladder Logic: Scale with parameters
- Thread starter Zephyr
- Start date
Mickey
Lifetime Supporting Member
That's the way the instruction works, it just a straight line equation.
It will keep on going.
If you want it to be clamped at your output high or low then check the input for limits before executing the SCP instruction. See picture below
It will keep on going.
If you want it to be clamped at your output high or low then check the input for limits before executing the SCP instruction. See picture below
Last edited:
Mickey
Lifetime Supporting Member
What processor do you have? Some support online editing.
Mickey, your example code will not clamp the output corresponding to max input, it simply stops executing the SCP when the input value is outside the Min/Max Input Range.
If the input value step-changed from 4000 to 5001, the output would not go to 65.
It would be better to clamp the output of the SCP with two rungs
GRT N7:1 65 MOV 65 N7:1
LES N7:1 59 MOV 59 N7:1
If the input value step-changed from 4000 to 5001, the output would not go to 65.
It would be better to clamp the output of the SCP with two rungs
GRT N7:1 65 MOV 65 N7:1
LES N7:1 59 MOV 59 N7:1
Mickey
Lifetime Supporting Member
Your right of-course.
The code I posted says if the operator enters an invalid value
( outside the limits) the corresponding out will not change.
This forces the operator to enter a valid value ( within limits).
Nothing wrong with your example though. But it does allow the operator to enter invalid values.
bernie_carlton
Lifetime Supporting Member + Moderator
Is it possible to implement the limits on the operator in the display program numeric input object?
Mickey
Lifetime Supporting Member
Do it both places. (PLC and HMI/SCADA) On SCADA systems I have even programmed a pop-up message telling them they screwed up.
( "Invalid Data Enter")
valski gonzaga
Member
Hi,I have a proximity sensor that will count the speed/rpm of a machine. can this be possible to use a digital input module (siemens plc s7300)and have it program to read the rpm/speed on the tp170HMI? any example please? thanks
Please give an example of how to execute in the rungs. Thanks
Mickey
Lifetime Supporting Member
Mickey
Lifetime Supporting Member
Your choice. You really don't need both though.
IMO, I prefer the limit because it stops the operator from entering an invalid number.
With the GRT,LES method the operator can still enter an invalid number although it will be clamped.
Since operators are unaware that attempting to make the speed faster than 65 will take the speed to 0 (They'll freak out and start pushing any button that blinks) then I should probably use the GRT and LES functions. You guys are great. Thanks a bunch.
Mickey
Lifetime Supporting Member
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.
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