1、Transmission SystemsAPI RECOMMENDED PRACTICE 552FIRST EDITION, OCTOBER 1994REAFFIRMED, FEBRUARY 2007Transmission SystemsManufacturing, Distribution and Marketing DepartmentAPI RECOMMENDED PRACTICE 552FIRST EDITION, OCTOBER 1994REAFFIRMED, FEBRUARY 2007SPECIAL NOTES1. API PUBLICATIONS NECESSARILY ADD
2、RESS PROBLEMS OF A GENERALNATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE,AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED.2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANU-FACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIPTHEIR EMPLOYEES AND OTHERS EXPOSED
3、CONCERNING HEALTH ANDSAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONSUNDER LOCAL, STATE, OR FEDERAL LAWS.3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPERPRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI-TIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER,
4、OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.4. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED ASGRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANU-FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCTCOVERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING
5、CONTAINEDIN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINSTLIABILITY FOR INFRINGEMENT OF LETTERS PATENT.5. GENERALLY, API STANDARDS ARE REVIEWED AND REVISED, REAF-FIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS. SOMETIMES AONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THISREVIEW CYCL
6、E. THIS PUBLICATION WILL NO LONGER BE IN EFFECT FIVEYEARS AFTER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR,WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION.STATUS OF THE PUBLICATION CAN BE ASCERTAINED FROM THE APIAUTHORING DEPARTMENT TELEPHONE (202) 682-8000. A CATALOG OF APIPUBLICA
7、TIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATEDQUARTERLY BY API, 1220 L STREET, N.W., WASHINGTON, D.C. 20005.Copyright 1994 American Petroleum InstituteiiiFOREWORDThis publication reflects the current practices in the transmission of instrument measure-ment and control signals in a refinery.Th
8、roughout this publication, soft-conversion (calculated) units are provided in paren-theses following actual units. Soft-conversion units are provided for the users referenceonly.API publications may be used by anyone desiring to do so. Every effort has been madeby the Institute to assure the accurac
9、y and reliability of the data contained in them; however,the Institute makes no representation, warranty, or guarantee in connection with this publi-cation and hereby expressly disclaims any liability or responsibility for loss or damageresulting from its use or for the violation of any federal, sta
10、te, or municipal regulation withwhich this publication may conflict.Suggested revisions are invited and should be submitted to the director of the Manufac-turing, Distribution, and Marketing Department, American Petroleum Institute, 1220 LStreet, N.W., Washington, D.C. 20005.vCONTENTSPage1 Scope 12
11、References 13 General . 13.1 Advantages of Transmitted Signals 13.2 Design Considerations for Transmission Systems . 13.3 Electronic . 13.4 Pneumatic . 13.5 Fiber Optics 23.6 Digital Field Bus 24 General Information on Electronic Systems 24.1 General . 24.2 Standard Electronic Signal Ranges 34.3 Reg
12、ulatory Codes and Recommended Practices 35 Reducing Electrical Interference in Electronic Systems 35.1 Sources of Electrical Interference 35.2 Minimizing Unwanted Voltages in Signal Transmission Circuits . 45.3 Instruments to be Interconnected . 56 Engineering Factors in Selection of Wire Types for
13、Electronic Systems 66.1 Process Controls with Milliampere Signals . 66.2 Process Controls with Voltage Signals. 66.3 Digital Communications Signals 76.4 Process Control Low Energy/Voltage Sensors. 76.5 Process Control with Pulse Output Meters 76.6 Low-Impedance Sensors to Computers 76.7 Turbine Mete
14、rs . 76.8 Magnetic-Flow Transmitters 77 Specifications for Wires and Cables in Electronic Systems. 77.1 Wire Size 77.2 Stranded Wire. 77.3 Insulation 87.4 Temperature Rating 87.5 Overall Jacket. 87.6 Shielding. 87.7 Number of Crossovers 87.8 Wire and Pair Identification . 87.9 Communication Wires 87
15、.10 Lightning Protection. 88 Typical Applications of Wire Types Used in Electronic Systems 89 Guidelines for Separation of Wires in Electronic Systems 89.1 Similar Signal Levels . 89.2 Signal and Power Wiring 89.3 Proximity to AC Fields 910 Effect of Transmission Distance on Electronic Signal Instal
16、lations 911 High Temperature Areas 912 General Information on Installation Methods for Electronic Systems. 913 Installation of Trays for Electronic Systems 913.1 Locations and Advantages . 913.2 Description . 914 Installation of Raceways in Electronic Systems. 1114.1 General . 11viPage14.2 Abovegrou
17、nd Installations 1114.3 Underground Installations 1114.4 Routing . 1215 Messenger Cable 1216 Surge Protection for Cables in Electronic Systems 1216.1 General . 1216.2 Types of Electrical Surges 1316.3 Types of Protective Devices. 1316.4 Selection and Installation of Surge Protection Devices . 1617 W
18、iring for Field Mounted Process Instruments . 1917.1 Leakage of Process Fluid . 1917.2 Moisture . 1917.3 Temperature 1917.4 Typical Wiring Practice 1917.5 Factory Sealed Enclosures . 1917.6 Non-Incendive Design (Division 2), Intrinsically Safe Design (Division 1), Purged Enclosures, and MI Cable Ins
19、tallations . 1917.7 Drainage Requirements 1917.8 Other Seal Requirements 1918 Junction Boxes . 1918.1 Use of Boxes 1918 2 Factors in Box Selection 1918.3 Box Design. 2118.4 Interior Color 2218.5 Mounting of Boxes. 2218.6 Mounting of Terminal Strips 2318.7 Ground Continuity for Shields . 2319 Control
20、 Room Wiring. 2319.1 General . 2319.2 Field Wiring Terminations . 2319.3 Other Control Wiring . 2319.4 Precautions For Power Supply Wiring. 2320 Installation of Grounding for Electronic Systems 2420.1 General . 2420.2 Definition of Terms 2420.3 Quality of Instrument-Circuit Ground Systems . 2420.4 T
21、esting of Grounds . 2520.5 Ground Electrodes 2520.6 Grounding of Transmission Circuits 2620.7 Grounding of Cable Shields . 2620.8 Grounding of DES Termination Room and Control Panelboards 2820.9 DES and Panelboard Ground Buses. 2820.10 Grounding of Instrument Cases 2820.11 Grounding of Conduits and
22、Wireways. 2820.12 Grounding Considerations Where Cathodic Protection is Used 2821 General Information on Pneumatic Systems 2921.1 Scope 2921.2 Air Supply Systems 2921.3 Pneumatic Transmission Systems 3422 Installation of Pneumatic Systems . 3722.1 General . 3722.2 Field-Routed Tubing Installations 3
23、722.3 Junction Box. 37viiPage22.4 Transmission Tubing Installations 3723 Cleaning And Pressure Testing of Pneumatic Tubing 3723.1 General . 3723.2 Cleaning . 3723.3 Pressure and Leak Testing 3723.4 Processing Plant Installations. 3723.5 Collection Points 3723.6 Transmission Tubing 38APPENDIX AABBREV
24、IATIONS USED IN FIGURES. 41Figures1Vertical Tray 132Vertically Mounted Long Span Tray. 143Typical Application and Location of Lightning Protective Devices. 154Typical Installation Of Lightning Protective Device for Personnel Safetyat One End of a Signal Pair. 165Typical Three-Terminal Gas-Filled Gap
25、 Arrester and Diode Shunt Lightning Protector 176Typical Carbon Air Gap and Diode Shunt On A-C Signal Transmission. 187Typical Junction Box. 208Panelboard Wiring Terminating Field Wiring at Instruments. 219Panelboard Wiring Terminating Field Wiring at Panel-MountedJunction Box . 2110Panelboard Wirin
26、g Terminating Field Wiring at Separate Junction Box 2211Computer Floors 2312Single-Point Ground Scheme 2513Total Single-Point Ground 2614Ground Electrode for One Low-Conductivity Soil Condition 2715Panelboard Grounding 2816Air Supply Piping for Field Instrument 2917Instrument Air Supply System with
27、Standby Compressor and Optional Plant Air Backup 3018Instrument Air Supply System from Plant Air with Instrument Air Standby as Air Backup 3119Instrument Air Supply System Using a Centrifugal Compressor . 3220Typical Instrument Air Supply and Subheader Piping 3421Methods Of Supporting Single Tubes a
28、nd Tubing Bundles at the Processing Unit . 3522Enclosed Jucntion Box Configurations. 36Tables1Specific Applications With Wiring Requirements, Wire Type, and Environment 22Power Level Classification . 43Wire Separation. 54Types of Wire or Cable for Signal Transmission 65Guidelines for Grouping Wires
29、Bearing Signals of the Same Magnitude 66Resistance Of Copper Wire - Per Conductor 67Line Sizing Guide for Pipe Headers 341 ScopeThis document reviews the recommended practices for theinstallation of electronic and pneumatic measurement andcontrol-signal transmission systems. It does not discusslease
30、d wire, radio, and telemetering transmission. Themethods described are generally used throughout the UnitedStates. These methods are based on the assumption that thefield devices, such as measuring transmitters, transducers,valve positioners, control valves, and other devices are prop-erly installed
31、. It is also assumed that the wiring, piping, andtubing at the control panel or Distributed Control System areproperly installed. See the other appropriate API Recom-mended Practices and standards as needed.2 ReferencesThe following publications are cited in this recommendedpractice:APIRP 500 Classi
32、fication of Areas for Electrical Installa-tions at Petroleum FaciltiesRP 540 Electrical Installations in Petroleum Pro-cessing PlantsASTM1A 123 Specification for Zinc (Hot-Dip Galvanized)Coatings on Iron and Steel ProductsA 525 Specification for General Requirements forSteel Sheet, Zinc-Coated (Galv
33、anized) by theHot-Dip ProcessISA2RP 12.6 Installation of Intrinsically Safe Systems forHazardous (Classified) Locations (ANSI3/ISARP 12.6)S7.4 Air Pressures for Pneumatic Controllers, Trans-mitters, and Transmission Systems (ANSI/ISAS7.4)S7.7 Recommended Practice for Producing QualityInstrument Air
34、(ANSI/ISA S7.7)S12.4 Instrument Purging for Reduction of HazardousArea ClassificationS50.1 Compatibility of Analog Signals for ElectronicIndustrial Process Instruments (ANSI/ISA S50.1)NEMA4250 Enclosures for Electrical Equipment (ANSI/NEMA 250) 1American Society of Testing and Materials, 1916 Race S
35、treet, Philadel-phia, PA 19103.2Instrument Society of America, P.O. Box 12277, Research Triangle Park,NC 27709.3American National Standards Institute, 11 West 42nd Street, New York,NY 10036.NFPA570 National Electric Code (NEC) (ANSI/NFPA70) 78 Lightening Protection Code (ANSI/NFPA 78) 493 Intrinsica
36、lly Safe Apparatus in Division IHazardous Locations496 Purged and Pressurized Enclosures for Elec-trical Equipment (ANSI/NFPA 496)3 General3.1 ADVANTAGES OF TRANSMITTED SIGNALSTransmission systems permit operation of one or morelarge or small process units from a remote control center. 3.2 DESIGN CO
37、NSIDERATIONS FORTRANSMISSION SYSTEMSThe following major factors should be considered in thedesign of transmission systems:a. The relationship of time constants among process, trans-mission, and control lines, since this relationship mayinfluence a control loops actual performance. Thisproblem is pri
38、marily associated with pneumatic transmis-sion.b. The reliability of air and electric power supplies.c. The routing and installation of tubing, wiring, and pipingto maintain circuit integrity; to reduce the possibility ofdamage from fire, overheating from hot process lines orequipment, and mechanica
39、l abuse; and to ensure immunityfrom electrical and radio-frequency interference. d. The resistance of material and construction to corrosioncaused by chemicals in the atmosphere or splatter fromnew construction or maintenance. e. Provisions for manual control, testing, and ready accessto instruments
40、 for maintenance. f. Safety requirements and the effect of federal, state, andlocal regulations and of national and local codes.3.3 ELECTRONIC The preferred signal transmission today is electronic.Electronic methods and needs are discussed in depth in thisdocument, starting with Section 4.3.4 PNEUMA
41、TIC Pneumatic signals are used today primarily in older plantsand where there is a special advantage to pneumatics. TheTransmission Systems14National Electrical Manufacturers Association, 2101 L Street, N.W., Wash-ington, DC 20032.5National Fire Protection Association, 1 Batterymarch Park, Quincy, M
42、A02269.2 API RECOMMENDED PRACTICE 552advantages, needs, and recommended methods are discussedin this document, starting with Section 21.3.5 FIBER OPTICSFiber optics is the phrase applied to the use of transparentglass or plastic fibers to carry light signals between devices.Fiber optics is a maturin
43、g technology and will find more use inthe future. At present, use is usually limited to dedicated cablesbetween portions of control systems, and for some specialapplications. Cables, connectors, and matching electronics areavailable. The user is cautioned to verify that the cable selectedis appropri
44、ate for the application in strength and mechanicalmakeup, and that the electronics are appropriate. If the signalpower is limited to Light Emitting Diode (LED), sources,rather than a Laser source, there is little concern of ignition ofhazardous vapors. If the cable has no metal components whichcould
45、 carry electrical currents, then fiber optics providescomplete electrical, galvanic, isolation between the connecteddevices, thus eliminating concerns of ground currents. 3.6 DIGITAL FIELD BUSSeveral proprietary digital communications schemes areavailable today for field instruments, and standards a
46、re underdevelopment to permit convenient interconnection. Digitalcommunications between microcomputer-based devices canutilize the intelligence of the devices to improve accuracy, toimprove utility, to reduce check-out costs, and to facilutatefurther advances in control and control systems. These te
47、ch-niques also allow multiple devices to share one wire pair toreduce wiring costs. Where metallic wiring is used, the usualconcerns of grounding, electrical surge, and electrical safetyall apply.4 General Information On ElectronicSystems4.1 GENERALThis section includes practices for classified and
48、non-clas-sified areas. The discussion of electric signal transmissionnecessarily includes signals, analog or digital, that are usedin measurement and control systems. The instrumentsinclude sensing elements, transmitters, analyzers, con-trollers, and display devices. The installation of signal wirin
49、g requires practices thatwill prevent excessive distortion of the signal. Signal wiringis only part of an electronic signal transmission system. Thedesign and installation of the wiring, transmitter, andreceiver must result in a system that is suitably accurate forthe application. Factors that must be considered includeregulatory codes, requirements of a specific set of equip-ment, and electrical characteristics of the environmentthrough which the wiring passes. This document describesfrequently encountered instruments and associated equip-Table 1Specific
