ISA TR5 1 01 TR77 40 01-2012 Functional Diagram Usage.pdf

1、 TECHNICAL REPORT ISA-TR5.1.01/ISA-TR77.40.01-2012 Functional Diagram Usage Approved 10 August 2012ISA-TR5.1.01/ISA-TR77.40.01-2012 - 2 - Copyright 2012 ISA. All rights reserved. ISA-TR5.1.01/ISA-TR77.40.01-2012 Functional Diagram Usage ISBN: 978-1-937560-06-5 Copyright 2012 by ISA. All rights reser

2、ved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher.

3、 ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709 - 3 - ISA-TR5.1.01/ISA-TR77.40.01-2012 Copyright 2012 ISA. All rights reserved. Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ISA-TR5.1.01/ISA-TR7

4、7.40.01-2012. This document has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms

5、 and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards and Practices Department is aware of the growing nee

6、d for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the m

7、etric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible . Standard for Use of

8、the International System of Units (SI): The Modern Metric System, published by the American Society for Testing provides outputs in response to external inputs and internal logic (NFPA 85: Boiler and Combustion Systems Hazards Code, 2011 Edition) 3.14 macro: a set of functions combined as a specific

9、 program to be run as a single task. The task is a subset of the controllers program but executes repeatedly for similar devices or applications with unique inputs and outputs. 3.15 measurement: the determination of the existence or the magnitude of a variable ISA-51.1-1979 (R1993) 3.16 multiple inp

10、ut multiple output: an algorithm/program, such as model predictive control, neural net, expert system, etc., that computes one or more output demands, biases, or setpoints based on multiple inputs 3.17 process: any operation or sequence of operations involving a change of energy, state, composition,

11、 dimension, or other properties that may be defined with respect to a datum ISA-51.1-1979 (R1993) 3.18 process measurement: the acquisition of information that establishes the magnitude of process qualities. ISA-51.1-1979 (R1993) 3.19 process variable: any variable property of a process; used in thi

12、s standard to apply to all variables other than instrument signals ISA-51.1-1979 (R1993) 3.20 program: a repeatable sequence of actions that defines the status of outputs as a fixed relationship to a set of inputs 3.21 setpoint: an input variable that sets the desired value of the controlled variabl

13、e; may be manually set, automatically set, or programmed. Its value is expressed in the same units as the controlled variable. 4 Abbreviations (Acronyms) HMI human machine interface I/O input/output MIMO multiple input multiple output MOV motor operated valve PID - proportional integral derivative -

14、 13 - ISA-TR5.1.01/ISA-TR77.40.01-2012 Copyright 2012 ISA. All rights reserved. 5 Preparation of functional diagrams This report is concerned with the functional diagrams normally prepared in the early stages of system conception from the mechanical or process flow sheet. Functional diagrams normall

15、y are revised and kept current over the complete system life cycle as system design progresses through the various stages of negotiations, quotation, contract award, reduction to final equipment, system checkout, installation, and ongoing system enhancements. They are also included as part of the sy

16、stem instructions. The functional diagrams define functions of a control configuration that are independent of the hardware and firmware of the control system used for process automation. Functional diagrams are a method to document application software and transfer information for implementation in

17、to the selected control system. A functional diagram may be more or less detailed, depending on its intended use. The amount of detail in a logic diagram depends on the degree of refinement of the logic and on whether auxiliary, essentially non-logic, information is included. Simplified diagrams can

18、 be drawn by omitting details that may be obvious. This report is intended to provide sufficient information to enable anyone with a reasonable amount of process and instrumentation knowledge, who is reviewing documents depicting process measurement and control, to understand the means of measuremen

19、t and control of the process. This report is suitable for use whenever reference to measurement and/or control instrumentation, control devices and/or functions, or software applications and/or functions is required for the purposes of symbolizing and identification. 5.1 Basic symbols A logic symbol

20、 comprises an outline or a combination of outlines together with one or more qualifying identifications and/or qualifying texts. Basic and complex logic symbols with minimum inputs need not specify input names. Logic symbols with multiple inputs can have input name identifiers to specify the signal

21、functions within the algorithm. New function or algorithm symbols should represent an encapsulated software component (i.e., function block) that exists within a systems library. 5.2 Advanced symbols With the introduction of microprocessor-based systems, suppliers have developed advanced algorithms

22、that are not represented by previous PMC 22.1, the German Institute for Standardization (DIN), the International Electrotechnical Commission (IEC), or ISA-5.1 standards. While following the intent of these standards, suppliers either create a new symbol or group existing symbols to represent the new

23、 algorithm. The problem occurs in understanding what function that symbol really represents and the symbols boundaries. Thus, advanced symbols depict new control algorithms via a combination of existing symbols, new control algorithms with multiple functions, and new control algorithm s previously u

24、navailable with electric analog systems. ISA-TR5.1.01/ISA-TR77.40.01-2012 - 14 - Copyright 2012 ISA. All rights reserved. 5.2.1 Combination of symbols A control algorithm containing multiple mathematical functions may be represented by combining multiple symbols within one block, as shown in Figure

25、5.2.1.a (PID controller), or by having the blocks physically touching each other along the longer dimension of the block, as shown in Figure 5.2.1.b (Mathematical function). The combination of mathematical symbols should only be used where there is no possibility of misunderstanding the function bei

26、ng represented. Combining symbols is often necessary to conserve space on a diagram. With the exception of arithmetic blocks, only single-input, single-output blocks should be combined with each other, and the inputs to the difference and summing blocks must always be shown as separate inputs and no

27、t as a combination with any other symbol or block. These combination symbols clearly explain the intended control algorithm. If a simplified combination of symbols is used to represent a complex control algorithm, the chosen simplified combination of symbols must represent one and only one control a

28、lgorithm. In no case should the combination of symbols or blocks be used as a means of representing a specific suppliers implementation of an algorithm or controller. Either the suppliers implementation should be fully detailed in the legend sheet in which it is used, or combined symbols should be s

29、hown as a new algorithm block, as defined in 5.2.3. For example, Figure 5.2.1.c includes a PID combination symbol. This symbol could represent control algorithm “b” or control algorithm “a.” If the PID combination symbol represents control algorithm “a”, a legend sheet should be provided to clearly

30、describe the symbols function. DP IP I D c o n t r o l l e rF i g u r e 5 . 2 . 1 . aM a t h e m a t i c a l f u n c t i o nF i g u r e 5 . 2 . 1 . b Example of Median Select 5.3 Diagram format This section discusses several methods to prepare a functional diagram. 5.3.1 Diagram organization A set o

31、f functional diagrams typically consists of multiple sheets: 1) title page, including the name of the functional group, revision, status, and date of the document; 2) table of contents, indicating the names of the subsections, the revisions, diagram numbers, and sheets; 3) legend sheet(s); and 4) in

32、dividual functional diagrams. 5.3.2 Diagram interconnection 5.3.2.1 Inputs and outputs may show connections to or from the actual process as well as other diagrams within the same logic system or other logic systems. 5.3.2.2 Process measurements or interconnections from another logic system required

33、 on another sheet should have single output interconnections with single/multiple reference to other sheets. 5.3.2.3 Process measurements should be identified by their instrument tag name. Tag descriptions, tag ranges, etc., may also be provided. 5.3.2.4 Process measurements and inputs from other lo

34、gic systems should appear only on one sheet of a diagram. 5.3.2.5 Signal lines between instruments and function symbols or between function symbols shown on different diagrams should be drawn with an interconnecting symbol (arrow, box, etc.). In cases of signals connected to more than one sheet, the

35、 connection reference must identify all signal destinations by a method that includes sheet reference and unique connection identification detail. Those signals originating from another page are to reference the source sheet by a method that includes the sheet reference and unique connection identif

36、ication detail. The methods may include symbols and/or text at the input/output connections themselves, listing tables on the diagram itself, or listing tables on a separate diagram that is used only for such listing tables. The interconnection symbols/tables should indicate: - 19 - ISA-TR5.1.01/ISA

37、-TR77.40.01-2012 Copyright 2012 ISA. All rights reserved. a) Direction of signal flow, going to a symbol or coming from a symbol on another diagram. Arrowheads depicting direction of signal flow are used for clarity in diagram connections, including inputs and outputs. b) A page identifier (e.g., di

38、agram number, sheet number) should identify where logic signals go to or come from. Grid zone location is optional. c) An input signal description/statement should be stated in a noun-verb text. A binary output signal description/statement should be stated in a verb-noun text. The noun represents th

39、e function or device tag number or name. The verb represents the signals function (i.e., status, override, command, etc.). d) Diagrams containing both continuous and binary signals should be distinguished with the continuously variable signal as a solid line and a binary (on-off) signal as a dashed

40、line. The binary signal lines may be a solid line if on a separate binary logic diagram that does not contain continuously variable signal representation or if on an inset detail diagram. 5.3.2.6 When the description for binary signal is true, the value of the binary signal is logic one. 5.3.2.7 The

41、re may be misunderstanding of binary logic statements involving devices or functions that are not recognizable as inherently having only two specific alternative states. For example, if it is stated that a valve is not closed, this could mean either (a) that the valve is open fully or (b) the valve

42、is simply not closed, namely, that the valve may be in any position from almost closed to wide open. To aid accurate communication between writer and reader of the diagrams, the diagrams should be interpreted literally. Therefore, possibility (b) is the correct one. If a valve is an open-closed valv

43、e, then, to avoid misunderstanding, it is necessary to do one of the following: a) Develop the diagram in such a way that it says exactly what is intended. If the valve is intended to be open, then is should be so stated and not be stated as being not closed. b) Have a separate note specifying that

44、the valve always assumes either the closed or the open position. By contrast, a device such as a motor-driven pump is either operating or stopped, barring some special situations. To say that the pump is not operating usually clearly denotes that it has stopped. The following definitions apply to de

45、vices that have open, closed, or intermediate positions. The positions stated are nominal to the extent that there are differential gaps and dead-band in the instrument that senses the position of the device: open position: a position that is 100 percent open not-open position: a position that is le

46、ss than 100 percent open. A device that is not open may or may not be closed. closed position: a position that is zero percent open not-closed position: a position that is more than zero percent open. A device that is not closed may or may not be open. ISA-TR5.1.01/ISA-TR77.40.01-2012 - 20 - Copyrig

47、ht 2012 ISA. All rights reserved. intermediate position: a specified position that is neither fully open nor fully closed For a logic system having an input statement that is derived inferentially or indirectly, a condition may arise that will lead to an erroneous conclusion. For example, an assumpt

48、ion that flow exists because a pump motor is energized may be false because of a closed valve, a broken shaft, or other mishap. Factual statements, that is, statements based on positive measurements that a certain condition specifically exists or does not exist, are generally more reliable. 5.3.2.8

49、A logic signal may correspond physically to either the existence or the non-existence of an instrument signal, depending on the particular type of hardware system and the circuit design philosophy selected. For example, a high-flow alarm may be chosen to be actuated by an electric switch whose contacts open on high-flow. On the other hand, the high-flow alarm may be designed to be actuated by an electric switch whose contacts close on high flow. Thus, the high-flow conditions may be represented physically by the absence of an electric sign