1、Binary Logic Diagramsfor Process OperationsReaffirmed 13 July 1992ISA-5.2-1976 (R1992) Formerly ANSI/ISA-5.2-1976 (R1992)STANDARDISA The Instrumentation,Systems, andAutomation Society TMCopyright g227 1976 by the Instrument Society of America. All rights reserved. Printed in the UnitedStates of Amer
2、ica. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted in any form or by any means (electronic, mechanical, photocopying, recording, orotherwise), without the prior written permission of the publisher.ISA67 Alexander DriveP.O. Box 12277Research Triangle Park,
3、 North Carolina 27709ISA-5.2-1976 (R1992)Binary Logic Diagrams for Process OperationsISBN 0-87664-331-4ISA-5.2-1976 (R 1992) 3PrefaceThis preface is included for informational purposes and is not part of ISA-5.2-1976 (R1992).This Standard has been prepared as a part of the service of ISA toward a go
4、al 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, and asks that they be addressed to the Secretary, Standards and Practices Board, ISA
5、, 67 Alexander Drive, P.O. Box 12277, Research Triangle Park, NC 27709, Telephone (919) 549-8411, e-mail: standardsisa.org.The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in par
6、ticular, 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 metric system) in their business and professional dealings with other countries. Toward this end this Depart
7、ment will endeavor to introduce SI-acceptable metric units in all new and revised standards to the greatest extent possible. The Metric Practice Guide, which has been published by the American Society for Testing and Materials as ANSI designation Z210.1 (ASTM E380-76, IEEE Std. 286-1975), and furthe
8、r revisions, will be the reference guide for definitions, symbols, abbreviation, and conversion factors.It is the Policy of ISA to encourage and welcome the participation of all concerned individuals and interests in the development of ISA Standards. Participation in the ISA Standards making process
9、 by an individual in no way constitutes endorsement by the employer of that individual of ISA or any of the Standards which ISA develops.The system described in this Standard is intended to meet the needs of people who are concerned with the operation of process systems. The guide for the Standard w
10、as American National Standards Institute (ANSI) Standard Y32.14.1973, Graphic Symbols for Logic Diagrams, which the committee attempted to follow so far as practical for the intended users of the ISA Standard.The Committee also referred to National Electric Manufacturers Association Standards ICS 1-
11、102, Graphic Symbols for Logic Diagrams, whose symbols bear resemblance to those of the ANSI Standard, and ICS 1-103, Static Switching Control Devices, which may eventually be supplanted by ICS 1-102. Reference was also made to National Fluid Power Association Recommended Standard T.3.7.68.2, Graphi
12、c Symbols for Fluidic Devices and Circuits. In addition, numerous other industrial standards were reviewed.The following people served on the 1976 SP5.2 Committee:NAME COMPANYGeorge Platt, Chairman Bechtel Power CompanyEdward J. Blahut Procon Incorporated, Pacific OperationsSanford Chalfin Fluor Cor
13、porationLouis Costea Hunt-Wesson Foods, IncorporatedRussell C. Greer Bailey Meter CompanyRoy Lazar Carnation Company4 ISA-5.2-1976 (R 1992)Frank Mehle (deceased) Procon Incorporated, Pacific OperationGary L. Pierce Shell Oil CompanyChuck Simms Fisher Controls CompanyJohn Vance United Process Control
14、 SystemsRobert Woo Los Angeles Department of Water the logic diagram may or may not go so far as to specify the outcome if both the commands were to exist at the same time. In addition, explanatory notes may be added to the diagram to record the logic rationale.Non-logic information may also be adde
15、d, if desired, e.g., reference document identification, tag numbers, terminal markings, etc.In these ways, the diagram may provide the level of detail appropriate, for example, for communication between a designer of pneumatic circuits and a designer of electric circuits, or may provide a broad-view
16、 system-description for a plant manager.10 ISA-5.2-1976 (R 1992)3.3 The existence of 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 that are selected.
17、* 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 condition may be represented physic
18、ally by the absence of an electric signal or by the presence of the electric signal. The Standard does not attempt to relate the logic signal to an instrument signal of any specific kind.3.4 A logic symbol that is shown in Section 4 with three inputs A, B, and C is typical for the logic function hav
19、ing any number of two or more inputs.3.5 The flow of intelligence is represented by lines that interconnect logic statements. The normal direction of flow is from left to right, or top to bottom. Arrowheads may be added to the flow lines wherever needed for clarity, and shall be added to lines whose
20、 flow is not in a normal direction.3.6 A summary of the status of an operating system may be put in the diagram wherever it is deemed useful as a reference point or landmark in the sequence.3.7 There may be misunderstanding of binary logic statements involving devices that are not recognizable as in
21、herently 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) that the valve is simply not closed, namely, that it may be in any position from almost closed to wide open. To aid accurate
22、communication between writer and reader of the logic diagram, the diagram should be interpreted literally. Therefore, possibility (b) is the correct one.If a valve is an open-close valve, then, to avoid misunderstanding, it is necessary to do one of the following:1) Develop the logic diagram in such
23、 a way that it says exactly what is intended. If the valve is intended to be open, then it should be so stated and not be stated as being not closed.2) Have a separate note specifying that the valve always assumes either the closed or the open position.By contrast, a device such as a motor-driven pu
24、mp 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 devices that have open, closed, or intermediate positions. The positions stated are nominal to the extent that ther
25、e are differential-gap 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 less than 100-percent open. A device that is not open may or may not be closed.Closed position: a position that is ze
26、ro-percent open.*In process operations, binary instrument signals are commonly either ON or OFF. However, as a more general case, logic systems exist that make use of binary hardware having signals with two alternate real values, e.g., +5 volts and 3 volts. In positive logic, the more positive signa
27、l, +5 volts, represents the existence of a logic condition, e.g., pump stopped. In negative logic, the less positive signal, 3 volts, represents the existence of a logic condition of pump stopped.ISA-5.2-1976 (R 1992) 11Not-closed position: a position that is more than zero-percent open. A device th
28、at is not closed may or may not be open.Intermediate position: a SPECIFIED position that is greater than zero- and less than 100-percent open.Not-at-intermediate position: a position that is either above or below the SPECIFIED intermediate position.For a logic system having an input statement that i
29、s derived inferentially or indirectly, a condition may arise that will lead to an erroneous conclusion. For example, an assumption 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
30、 on positive measurements that a certain condition specifically exists or does not exist, are generally more reliable.3.8 A process operation may be affected by loss of the power supply* to memories and to other logic elements. In order to take such operating eventualities into account, it may there
31、fore be necessary to consider the effect of loss of power to any logic component or to the entire logic system. In such cases, it may be necessary to enter power supply or loss of power supply as logic inputs to a system or to individual logic elements. For memories, the consideration of power suppl
32、y may be handled in this manner or as shown in Sections 4.7b, c, and d.By the same token, it may be necessary to consider the effect of restoration of power supply.Logic diagrams do not necessarily have to cover the effect of logic power supplies on process systems but may do so for thoroughness.3.9
33、 It is recommended, for clarity, that a single time-function symbol, as appropriate, be used to represent each time function in its entirety. Though not incorrect, the representation of a complex or uncommon time function by using a time-function symbol in immediate sequence with a second time-funct
34、ion symbol or with a NOT symbol should be avoided (see Section 4.8).3.10 Process instrument symbols and designations follow ISA Standard 5.1-1973 (American National Standards Institute Standard Y32.20-1975), “Instrumentation Symbols and Designations.“ However, these symbols are included for illustra
35、tive purposes, only, and are not part of Standard 5.2.3.11 If a drawing, or set of drawings, uses graphic symbols that are similar or identical to one another in shape or configuration and that have different meanings because they are taken from different standards, then adequate steps shall be take
36、n to avoid misinterpretation of the symbols used. These steps may be to use caution notes or reference notes, comparison charts that illustrate and define the conflicting symbols, or other suitable means. This requirement is especially critical if the graphic symbols used, being from different disci
37、plines, represent devices, conductors, flow lines, or signals whose symbols, if misinterpreted, may result in danger to personnel or damage to equipment.4 SymbolsThe symbols for diagramming binary logic are defined as follows:*The term power supply covers the energizing medium, whether it be electri
38、c, pneumatic, or other.12 ISA-5.2-1976 (R 1992)ISA-5.2-1976 (R 1992) 1314 ISA-5.2-1976 (R 1992)ISA-5.2-1976 (R 1992) 1516 ISA-5.2-1976 (R 1992)ISA-5.2-1976 (R 1992) 1718 ISA-5.2-1976 (R 1992)5 BibliographyAmerican National Standards Institute Standard Y32.14-1973, Graphic Symbols for Logic Diagrams
39、(Two-State Devices).American National Standards Institute Standard X3.5-1970, Flowchart Symbols and Their Usage in Information Processing.International Electrotechnical Commission Recommendation, Publication 117-15, 1972, Binary Logic Elements.National Electric Manufacturers Association Standard ICS
40、 1-102, Graphic Symbols for Logic Diagrams.National Electric Manufacturers Association Standard ICS 1-103, Static Switching Control Devices.National Fluid Power Association Standard T.3.7.68.2, Graphic Symbols for Fluidic Devices and Circuits.ISA-5.2-1976 (R 1992) 19Appendix A General application ex
41、ampleA.1 IntroductionThis example uses a representative process whose instruments are denoted by the symbols of ISA-5.1-1973, (ANSI Y32.20-1975.) The process equipment symbols are included only to illustrate applications of instrumentation symbols. The example is not a part of Standard 5.2.A.2 Simpl
42、ified flow diagramFigure A.1 Tank filling operation simplified flow diagram20 ISA-5.2-1976 (R 1992)A.3 Word descriptionA.3.1 Pump startFeed is pumped into either tank A or tank B. The pump may be operated manually or automatically, as selected manually on a local maintained-output selector switch, H
43、S-7, which has three positions: ON, OFF, and AUTO. When the pump is operating, red pilot light L-8A is on; when not operating, green pilot light L-8B is on. Once started, the pump continues to operate until a stopping command exists or until the control power supply is lost.The pump may be operated
44、manually at any time provided that no trouble condition exists: The suction pressure must not be low; the seal water pressure must not be low; and the pump motor must not be overloaded and its starter must be reset.In order to operate the pump automatically, all the following conditions must be met:
45、A.3.1.1 Board-mounted electric momentary-contact hand switches, HS-1 and HS-2, start the filling operation for tanks A and B, respectively. Each switch has two positions, START and STOP. START de-energizes the associated solenoid valves, HY-1 and HY-2. De-energizing a solenoid valve causes it to go
46、to the fail-safe position, i.e., to vent. This depressurizes the pneumatic actuator of the associated control valves, HV-1 and HV-2. Depressurizing a control valve causes it to go to the fail-safe position, i.e., to open. The control valves have associated open-position switches, ZSH-1 and ZSH-2, an
47、d closed-position switches, ZSL-1 and ZSL-2.The STOP position of switches HS-1 and HS-2 causes the opposite actions to occur so that the solenoid valves are energized, the control valve actuators are pressurized, and the control valves close.If starting circuit power is lost, the starting memory is
48、lost and the filling operation stops. The command to stop filling can override the command to start filling.To start the pump automatically, either control valve HV-1 or HV-2 must be open and the other control valve must be closed, depending on whether tank A or tank B is to be filled.A.3.1.2 The pu
49、mp suction pressure must be above a given value, as signalled by pressure switch PSL-5.A.3.1.3 If valve HV-1 is open to permit pumping into tank A, the tank level must be below a given value, as signalled by level switch LSH-3, which also actuates a board-mounted high-level pilot light, LLH-3. Similarly, high-level switch, LSH-4, permits pumping into tank B, if not actuated, and actuates pilot light LLH-4, if actuated.A.3.1.4 Pump seal water pressure must be adequate, as indicated on board-mounted receiver gage, PI-6. This is a non-interlocked requirement that depends on the operato
