API RP 552:1994(R2007) pdf download.Transmission Systems
1 Scope
This document reviews the recommended practices for the installation of electronic and pneumatic measurement and control-signal transmission systems. It does not discuss leased wire, radio, and telemetering transmission. The methods described are generally used throughout the United States. These methods are based on the assumption that the field devices, such as measuring transmitters, transducers, valve positioners, control valves, and other devices are prop- erly installed. It is also assumed that the wiring, piping, and tubing at the control panel or Distributed Control System are properly installed. See the other appropriate API Recom- mended Practices and standards as needed.
3 General
3.1 ADVANTAGES OF TRANSMITTED SIGNALS Transmission systems permit operation of one or more large or small process units from a remote control center. 3.2 DESIGN CONSIDERATIONS FOR TRANSMISSION SYSTEMS The following major factors should be considered in the design of transmission systems: a. The relationship of time constants among process, trans- mission, and control lines, since this relationship may influence a control loopÕs actual performance. This problem is primarily associated with pneumatic transmis- sion. b. The reliability of air and electric power supplies. c. The routing and installation of tubing, wiring, and piping to maintain circuit integrity; to reduce the possibility of damage from fire, overheating from hot process lines or equipment, and mechanical abuse; and to ensure immunity from electrical and radio-frequency interference. d. The resistance of material and construction to corrosion caused by chemicals in the atmosphere or splatter from new construction or maintenance. e. Provisions for manual control, testing, and ready access to instruments for maintenance. f. Safety requirements and the effect of federal, state, and local 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 this document, starting with Section 4.
3.5 FIBER OPTICS
Fiber optics is the phrase applied to the use of transparent glass or plastic fibers to carry light signals between devices. Fiber optics is a maturing technology and will find more use in the future. At present, use is usually limited to dedicated cables between portions of control systems, and for some special applications. Cables, connectors, and matching electronics are available. The user is cautioned to verify that the cable selected is appropriate for the application in strength and mechanical makeup, and that the electronics are appropriate. If the signal power is limited to Light Emitting Diode (LED), sources, rather than a Laser source, there is little concern of ignition of hazardous vapors. If the cable has no metal components which could carry electrical currents, then fiber optics provides complete electrical, galvanic, isolation between the connected devices, thus eliminating concerns of ground currents.
API RP 552:1994(R2007) pdf download
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