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Interpretation of the ANSI/ISA-5.01.01 standard

Aug. 8, 2005
Process control authority Bela Liptak brings in specialists from his cadre of co-authors to answer a reader's question. Find out if they agree to the intepretation given with reference to the ANSI/ISA-5.01.01 standard.
QUESTION:INITALLY I would like to congratulate you, also your team, for the collection of Instrument's Handbook which I possess the third edition of "Process Software and Digital Networks." I am an Electrical Engineer, specialized in automation, and I have a problem with the interpretation of the ANSI/ISA-5.01.01 standard:In one determined petrochemical plant, the control system possesss some elements (servers, controllers, stations of supervision, converters and terminators of network, switches) that I understand to be able to be identified according to related standard. The devices of the network receive the data by means of a network from control, they effect its service and they read the results for the customers or write in the control system.The devices of the net follow listed to below:
  1. System of Distributed Control - DCS; 
  2. Advanced Process Control - APC; 
  3. Real Time Optimization - RTO; 
  4. OLE for Process Control - OPC; 
  5. WEB Server; 
  6. Operation Systems - Supervisory/

For the functions above, I related with the letters foreseen in the ANSI/ISA-5.01.01 standard, obeying the possible combinations. It follows below the respective correspondence with the previous sequence:

  1. NK - identification of the area - sequential: DCS; 
  2. NK - identification of the area - sequential: APC; 
  3. NK - identification of the area - sequential: RTO; 
  4. NY - identification of the area - sequential: OPC; 
  5. NKI - identification of the area - sequential: WEB Server; 
  6. NKI - identification of the area - sequential: Operation Systems.

The documents that I foresaw to identify the automation system are related below:

  1. Drawing of the architecture using the symbology of the ANSI/ISA-5.01.01 standard; 
  2. List of Segments; 
  3. List of Devices of Networks.

I am working in the creation of a datasheet for devices as switches and servers. I would like to know if you agree to the interpretation given with reference to the standard.

Marcos Castro


I AM RETIRED now. But years ago I was on the ISA 5.1/ 5.3 committee, when DCS and PLC's just started. The ISA 5.1 symbols represent  I/O's  and basic control functions only (which variable is being controlled, not how).

Thus, system architecture cannot be described by it. Neither can control algorithms. I had suggested a special set of symbols for those, but the committee did not want to go there, because algortithms, platforms and software are changing too fast. ISA 5.3 was a compromise. However, ISA 5.06 "Functional Requirements - Documentation for Software Applications" is a great tool that can also be used for batch control.

In my work with refineries, we have often created supplementary symbols, such as dotted or hyphened liens to distinguish which I/O goes to the PLC and which to the DCS rack. ISA 5.3 is tolerant to creating supplemental symbols for company use.

Stephan Gaertner, P.E. Control Systems, San Francisco

REFER TO page 4 of the 4th edition of Volume 1 of the Instrument Engineer’s Handbook for “ Flowsheet and P&I Diagram Symbols and see page 31 of the same volume for “Functional Diagram and Function Symbols”.  

Béla Lipták


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