RS Logix 5000-Would like to remove several digits to the right of the decimal point ?

Baker in Virginia

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• Dec 28, 2018

• #1

Good Afternoon ,

I have a number like .025690034 and I'm trying to keep a plate gap of .025 that has a motor driving it. This 3 phase motor keeps going up and down trying to keep the position of .025690034 , when all it needs to do is keep .025. I once used the instruction Truncate (TRN) , but that takes all the numbers to the right away of the decimal point.

Do you guys know of a simple way of doing this ?

Thanks so much ,

 

TheWaterboy

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• Dec 28, 2018

• #2

Multiply by 1000, then move that to a Dint

 

RonJohn

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• Dec 28, 2018

• #3

Along with The Waterboy's suggestion, you could probably try a LIM instruction too. This would incorporate a type of deadband around your setpoint.

 

Baker in Virginia

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• Dec 28, 2018

• #4

Ok , what I did was take .2018163 ( Really my number ) and Multplied that by 1000. Got 201.8163 . Then I used a TRN ( in Math Conversions instruction tab ) and got 201.0. The TRN took everything off to the right of the decimal. I then multiplied it by .001 , then I got .201 .

 

rupej

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• Dec 28, 2018

• #5

Sounds like your controls need some deadband rather than just lowering the resolution.

 

Rob S.

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• Dec 28, 2018

• #6

What is deadband really and how would you implement it in your RS Logix 5000 code ?

 

OkiePC

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• Dec 28, 2018

• #7

Rob S. said:

What is deadband really and how would you implement it in your RS Logix 5000 code ?

Click to expand...

Tolerance: "Close enough, stop trying."

UpperLimit = Target +0.05
LowerLimit = Target - 0.05

(Instead of 0.05, use deadband/2 if you want it to be adjustable)...

If actual value is within those LIMits, then that's good enough and quit moving...

 

TheWaterboy

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• Dec 31, 2018

• #8

Baker in Virginia said:

Ok , what I did was take .2018163 ( Really my number ) and Multplied that by 1000. Got 201.8163 . Then I used a TRN ( in Math Conversions instruction tab ) and got 201.0. The TRN took everything off to the right of the decimal. I then multiplied it by .001 , then I got .201 .

Click to expand...

2 things to note, the number "should" have been rounded to .202, MOV instruction will do that for you (I think... I've been on a really good vacation for a couple weeks so I have forgotten almost everything I ever knew about work), but if rounding isn't important, if you do any math on that REAL number again, or potentially even if that root number changes in the right way, you will have additional digits to the right.

Such is the world of binary math.