This Guide covers basic requirements for the design, installation, and testing of transmitters and receivers. The manufacture and models of transmitters should be standardized where possible. Equipment shall be selected to suit the intended environment with due consideration.
This Guide covers basic requirements for the design, installation, and testing of transmitters and receivers. The manufacture and models of transmitters should be standardized where possible. Equipment shall be selected to suit the intended environment with due consideration.
This Guide covers basic requirements for the design, installation, and testing of transmitters and receivers. The manufacture and models of transmitters should be standardized where possible. Equipment shall be selected to suit the intended environment with due consideration.
This Guide covers basic requirements for the design, installation, and testing of transmitters and receivers. The manufacture and models of transmitters should be standardized where possible. Equipment shall be selected to suit the intended environment with due consideration.
TABLE OF CONTENTS 1. Scope 2. References 3. General 4. Transmitters 4.1 General 4.2 Pneumatic 4.3 Electronic 5. Receivers 5.1 General 5.2 Pneumatic 5.3 Electronic 6. Scales 7. Charts and Chart Drives History of Change 1. SCOPE This Guide covers basic requirements for the design, installation, and testing of transmitters and receivers. 2. REFERENCES The following publications form a part of this Guide. The references cited with dates in this Guide were used in its development. For all references which have been superseded, revised, and/or corrected, the user of this Guide is obligated to determine if the latest versions of the cited references have any impact on the content of this Guide or its use. Mobil Technology Company (MTC) Guide Sponsor should be consulted if there are any concerns or questions. Mobil Engineering Guides EGE 16-B-10 (1988) Piping Instruments EGE 16-B-30 (1994) Piping Materials and Service Classifications EGE 32-B-1 (1989) Instrumentation General Requirements ANSI (American National Standards Institute) Standard 913 (1988) UL Standard for Safety Intrinsically Safe Apparatus and Associate Apparatus for Use Hazardous Locations 3. GENERAL 3.1 The references and requirements of EGE 32-B-1 and ANSI 913 apply to this Guide. 3.2 All instrument loops shall consist of separate transmitter and receiver configurations. Exceptions, such as single head for a displacement level controller or a local single-case controller, shall be subject to Mobil approval. 3.3 All electrical or electronic instruments or devices for use in hazardous areas shall be approved for the installation location by a nationally recognized authority. Examples are Underwriters Laboratories (UL), MOBIL ENGINEERING GUIDE EGE 32-B-6 1994 PAGE 2 OF 6 APRIL 1994 Factory Mutual (FM), the Canadian Standards Association (CSA) in North America, and (BASEEFA) in Europe. 4. TRANSMITTERS 4.1 General 4.1.1 The manufacture and models of transmitters should be standardized where possible. Equipment shall be selected to suit the intended environment with due consideration of: (a) Electrical area classification. (b) Ambient temperature variations. (c) Thermal radiation. (d) Humidity. (e) Dust. (f) Vibration. (g) Atmospheric pollutants. 4.1.2 All transmitters shall be of the indicating type with integral indicator gages or, if blind, shall be provided with local indicator gages. Failure of local indication shall not cause failure of transmitter output. Elimination of local indicator gages shall require Mobil approval, and test connections shall be provided in its place. Indicator gages shall be located so that they are readable from a normal operating walkway or from ground level. In addition, they shall meet the requirements of Paragraph 5.1.5 of this Guide. Local electronic indicator gages shall be furnished with integrally mounted diodes to avoid interruption of the transmitted signal when the indicator gage is taken out of the loop. 4.1.3 Transmitters having a linear output throughout the sensing range may be used unless otherwise approved by Mobil. 4.1.4 When suppressed-range transmitters are used on critical loops, a parallel full-range transmitter shall be installed if required for startup of the unit. 4.1.5 Transmitters shall be as close coupled as possible, adequately supported, and easily accessible. A Mobil-approved valve manifold (see EGE 16-B-10) or a valving configuration that is adequately supported shall be provided to permit a zero check of the transmitter. Transmitters used in liquid sealed systems shall not be furnished with three-valve manifolds unless specifically approved by Mobil. Transmitters used in the measurement of hazardous materials such as chlorine, hydrogen chloride, or hydrogen fluoride shall be self- draining. 4.1.6 Where required by project location, lightning protection shall be provided by the instrument vendor as an integral part of, or a factory-assembled external addition to, the transmitter. 4.1.7 For critical temperature control points, field-mounted temperature transmitters are preferred. Thermocouples for controlling high-pressure reactors and other critical equipment may be used. 4.1.8 The material of transmitter sensing elements (capsules) shall be Type 316 stainless steel unless the process fluid requires a different material, such as Monel for HF service. Cadmium-plated carbon steel MOBIL ENGINEERING GUIDE APRIL 1994 PAGE 3 OF 6 EGE 32-B-6 1994 is not acceptable. Instrument body material shall be Type 316 stainless steel as a minimum and be consistent with, or exceed, the piping material specifications. 4.2 Pneumatic 4.2.1 Pneumatic transmitters shall have a linear output of 20 to 100 kPa gage or 0.2 to 1.0 bar gage (3 to 15 psig) throughout the measured range. The maximum transmission distance is 100 m (333 ft). Exceptions shall require Mobil approval. 4.2.2 Pneumatic transmitters shall be provided with a 6 mm (1/4 in.) tee and plugged valve for testing the output signal. The tee and plugged valve shall be of material specified in EGE 16-B-10. 4.3 Electronic 4.3.1 Microprocessor-based intelligent transmitters are preferred for critical control applications, for their accuracy, ease of maintenance, and greater stability. Intelligent transmitters with digital output mode signal shall be a maximum of 24 volts DC and not used for fast response loops (i.e. compressor anti-surge control). Use the 4 to 20 milliampere analog output mode signal. Conventional electronic transmitters shall have a DC output of 4 to 20 milliamperes and may be used for noncritical applications. Conventional transmitters with output signals of any other type shall require Mobil approval. Transmitters shall meet the hazardous area classification designated for their location. Intrinsic safety is the preferred design to meet the class of risk designated for the area. Other methods, such as nonincendive and explosionproof techniques, may be used with Mobil approval. Electronic transmitters, with or without barriers, shall be certified as intrinsically safe by a recognized authority. 4.3.2 As a minimum, electronic transmitters shall be of the DC current-regulating type and capable of operating with the power source located in a nonhazardous areas. These transmitters shall utilize a two-wire system for signal/power transmission. Exceptions shall require Mobil approval. Where applicable, microprocessor-based intelligent transmitters that can be range changed and calibrated on line may be used (see Paragraph 4.3.1). 4.3.3 Equipment shall not be susceptible to, or interfere with, hand-held radio transceivers operated in the immediate vicinity of the equipment. Equipment shall be capable of correct operation in a field strength of 10V/meter over a frequency range of 27-500 meghz at a distance of 1 m (.3 ft). 4.3.4 Electronic transmitters shall have noninteractive zero and span adjustments. 5. RECEIVERS 5.1 General 5.1.1 Any device that receives a transmitted signal representing the magnitude of a variable is a receiver. This includes the display portion as well as the control portion of a split-architecture system or any of the many operation interface devices currently available. 5.1.2 Central control room displays of process variables shall be achieved by a cathode ray tube (CRT) operator interface. One-on-one displays such as a traditional analog receiver or single microprocessor-based receiver may be considered, subject to Mobil approval. 5.1.3 If board-mounted receivers are approved, they shall be of the miniature type with a pullout chassis. High-density arrangements shall be used. MOBIL ENGINEERING GUIDE EGE 32-B-6 1994 PAGE 4 OF 6 APRIL 1994 5.1.4 CRT operator interface shall have the capacity of trend recording any indicated variable. The need for, and configuration of, additional trend-recording requirements shall be determined during the engineering phase of the project. 5.1.5 Whenever a control valve manipulates a variable and this variable has a transmitted signal, then a local indicator gage showing the output of the associated transmitter shall be provided and shall be readable at the control valve. If no transmitter is being used, a local process-variable indicator shall be provided at the valve. If a local indicator gage is used, failure or removal of this indicator shall not cause failure of the loop. Local indicator gages shall have a Type 316 stainless steel tag showing the transmitter number, service, and range. 5.2 Pneumatic Local indicator gages shall have a 100 mm (4 in.) minimum dial, with the spring or input range as well as the scale shown on the dial. For pneumatic indicator gages, 20 to 100 kPa gage or 0.2 to 1.0 bar gage (3 to 15 psig) is acceptable. 5.3 Electronic 5.3.1 Analog and digital signals from sensors shall be conditioned, if necessary, for input to any receiver display unit. A microprocessor-based controller or data acquisition unit shall be capable of receiving 4 to 20 milliamperes DC, millivolts, and digital signals. The controller system shall be capable of generating the required output signal necessary to operate the final control element; that is, a valve. Signal conditioning can linearize flow signals, thermocouples, resistance bulbs, etc. 5.3.2 Field-mounted multiplexers may be used for transmission of temperature points for indication in the central control room. 6. SCALES Scales for control room or local indicators shall be direct reading for pressure and temperature. Flow indicators shall be direct, linear, or zero to 10 square root, depending on the application. Level indication shall be direct reading or zero to 100 percent uniform. 7. CHARTS AND CHART DRIVES 7.1 Charts shall be zero to 10 square root and zero to 100 percent uniform for differential flow, depending on whether or not a square-root extractor is used. For all other miniature recorders, charts shall be zero to 100 percent uniform or as called for by the project specifications. Large-case temperature recorders shall be microprocessor based, incorporating linearization of the input signal. Accordingly, charts shall be linear. Combination charts shall be used where more than one variable is to be recorded. Multipoint temperature recorders shall have 150 mm (6 in.) or wider strip charts. A minimum scale width of 100 mm (4 in.) shall be used on all other charts. A minimum six month supply of charts and ink shall be provided for each recording instrument. 7.2 Chart drives for all electronic and electric recorders shall be synchronous AC electric motors. Switch-selectable, multispeed chart drives shall be pulsed stepping motor driven. Field units shall meet area classification. For locally mounted recorders in areas where electricity is not available or frequency control of AC power supply is not adequate to permit use of synchronous motors, chart drives may be spring wound, pneumatic, or gas activated as determined during the engineering phase of the project. MOBIL ENGINEERING GUIDE APRIL 1994 PAGE 5 OF 6 EGE 32-B-6 1994 Pneumatic chart drives shall be of the impulse type. If a pneumatic driving force other than air is used, local environmental requirements shall be met. 7.3 Charts and scales for locally mounted instruments shall have ranges in accordance with the units shown in Table 1. Charts and scales for other instruments shall have factors to convert to these units. TABLE 1 RANGES FOR LOCALLY MOUNTED INSTRUMENTS Measured Variable or Transmission API Preferred Customary Signals SI* Units Electronic signals 4 to 20 4 to 20 milliamperes milliamperes Air signals 20 to 100 kPa gage, 3 to 15 psig 0.2 to 1.0 bar gage Volumes m scf, bbl, US gal 3 Flow capacities m /day, m /h US gpm, scfh 3 3 bbl/d, lb/h, ton/h (steam flow) Pressures kPa gage, kPa abs, mm Hg, psi, psia, in. water, bar gage, bar abs, in. Hg. millibar Temperatures C F Analyzers As noted As noted (pH, %0 ) (pH, %0 ) 2 2 Level mm, % in., % * Units shall be subject to regional or local preference. MOBIL ENGINEERING GUIDE EGE 32-B-6 1994 PAGE 6 OF 6 APRIL 1994 HISTORY OF CHANGE The history of change contained herein does not constitute a complete listing of revisions and changes made to this document. Only revisions and changes of significant technical content (per sponsor and Steering Committee) are listed. EGE 32-B-6 1994 EGE 32-B-6 1994 supersedes the 1986 version with the following significant technical changes: 1. Thermocouples for controlling high pressure reactors and other critical equipment may be used. 2. Pneumatic signal transmission distance is not to exceed 100 m (333 ft) without Mobil approval. 3. The use of intelligent transmitters with digital output mode signal shall be avoided for fast response loops (i.e., compressor anti-surge control).