5 replies to this topic

[mes127]

Hello Everyone,

 

Our EPC company asked to provide a control logic diagram based on process control narrative for a hydrocarbon processing plant. However, I was asked specifically the diagram should be prepared in "negative logic" format. 

 

 

I did some internet search but there are limited sources on this, plus as a chemical engineer it makes more sense to me to see similar approach on a chemical process rather than other disciplines such electrical engineering.

I just wonder if someone could share with me with such a diagram for a typical unit operation with a few instruments?

 

Thank you

 

Max

[Pan Nata]

Hi Max,

 

I've never heard any kind of that document. For control logic, process/chemical eng. mostly deal with S.A.F.E charts, causes & effects matrix, and ESD Logic diagram.

[mes127]

Pan,

 

The documents you mentioned are also part of the package, but Control Logic is also a stand alone document.

 

Thank you

 

Max

[Saml]

As far as I know, "negative logic" means that low voltage means true, while high voltage means false.

This makes sense when you want to consider the loss of signal as a "true" value signal for an alarm or a switch that activates a logic.

 

But it may also mean writing the logic in the negative forms like A_AND_B = Neg(NegA_OR_NegB)

 

Say

Positive AND

True-True = True

True-False = False

False-True =False

False-False = False

 

equals to

Negative OR

False-False (Negative of True-True) = False (Negative is True)

False-True (Negative of True-False) = True (Negative is False)

True-False (Negative of False-True) = True (Negative is False)

True-True (Negative of False-False) = True (Negative is False)

 

Also Check This

http://hyperphysics....ic/gate.html#c2

[breizh]

hi ,

training materials are available on Youtube .

Good luck.

Breizh

[mes127]

Thank you everyone for your feedback.

 

Max