Control.com - Nerds in Control

Please let us know the procedure to prepare instrument logic diagrams or guide lines to prepare logic diagrams

mohammad.majidkhan@czfp.com

If anyone has answered this e-mail is it possible to have the answer posted for all to see??

Bob

To prepare Instrument Logic Diagrams, you should have some the required documents as below:
- P&ID
- Cause & Effect Diagram
- Logic Diagram Symbols

And some the following guidelines help you to prepare logic diagram:

1. Develop the logic diagram in such a way that it presents results in a positive logic format. For example, if the result of the logic operation is to completely open a valve, it should be so stated and not be stated as being “not closed.”

2. Use a specific separate label to indicate conditions of final control elements that have more than two responses to binary signal

3. Label each input and output of each set of logic operations on every sheet of the diagram

4. Label each external input or output for each sheet of the diagram so that its source and destination are clearly understood.

5. Adopt a standard set of logic symbols and instrument labels, and resist the temptation to modify your logic symbols for the “special situation” that inevitably develops. If the situation cannot be initially explained with relatively simple combinations of AND, OR, NOT, NAND, and NOR symbols, think about it some more until it can be done that way

6. Avoid using ladder diagrams or ladder diagram logic symbolism. These types of icons are useful when installing or troubleshooting the control scheme but are only routinely used and understood by a small percentage of the technical personnel who need to know about the process.

These useful rules of thumb all follow from one “golden rule.” If the binary logic diagram does not clearly, easily, and unambiguously indicate what is going on in the process, then the diagram is of marginal value and should be reworked until it does. Following this rule will increase the chances of having the diagram match what it is intended to say with what it actually says.