December 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
for pneumatic processes in particular but also, where reasonably precise analogies can be drawn, for all processes in general.
Acknowledgment This work was supported in part by funds of the Eugene Higgins Trust allocated to Princeton University. The helpful suggestions of C. E. Mason of the Bristol Co. and the assistance of George D. Kopperl in conducting preliminary studies and in assembling the analog are gratefully acknowledged.
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Literature Cited (1) Brown, G.S., and Campbell, D. P., “Principles of Servomechanisms,” New York, John Wiley & Sons, 1948. ( 2 ) Eckman, D. P., “Principles of Industrial Process Control,” New York, John Wiley & Sons, 1945. (3) Mason, C. E., private communication (1950). (4) ‘’Connor* J. A., No. 207-8 (5) Smith, E. S., “Automatic Control Engineering,” New York. McGraw-Hill Book Co., 1941. Eng.l
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R B C ~ I V EMay D 1, 1951.
The Instrument Engineer in Process Design T h e instrument engineer is relatively new to industry. Hie function as a member of a process design group in an engineering and construction firm is discussed, and the methods he uses to fulfill this function are described. The actual work required of the engineer is covered, and typical work sheets, specification forms, and other standards used by him are presented. This article is directed to the young engineer in the hope that it will help him to gain an understanding of the qualifications and duties of the instrument engineer engaged in the design of process plants.
J. N. Nonamaker Daw & Zfmmermann,Inc., I700 Saneom St., Philadelphia9Pa.
T
H E increasing complexity of chemical process operations, the necessity of reducing operating costs, and the demand for lower cost products able to meet more rigid quality specifications have probably been the most important factors in the development of modern instruments. Within the last decade, because of the rate of development and the resulting widespread application and specialized nature of industrial instrumentation, a new type of engineer-the instrument engineerhas been developed. Today, like other engineers, his services cover the fields of design, operation, and maintenance. I n this paper we are interested in the instrument engineer in the field of design, in particular that phase of engineering design that follows the research and development stages of an industrial project. The intent of this paper is to indicate the major duties of the instrument engineer and to discuss the work that he must accomplish in producing the instrumentation for a process. The comments contained herein are not limited t o any particular type of industrial plant but are applicable to all types. The actual work required of the instrument engineer will vary with the size of the plant only in so far as some of the items will not apply to relatively small projects since it would involve unreasonable engineering costs to undertake to complete them. The information presented represents some of the practices and methods used by an independent consulting engineering and construction firm. However, with minor changes it should be adaptable for use by plant engineering departments. The primary function of the instrument engineer is to analyze a process and, on the basis of the analysis, select an integrated system of instrumentation that will, in conjunction with associated equipment, produce the desired quality of product. To fulfill this function, the instrument engineer must have a working knowledge of the process and the process equipment involved; he must be familiar with the problems met in piping design; and he should be able to appreciate the factors involved in the electrical design for the process, in so far as it will be affected by the instrumentation. His work must be integrated
with that of the engineers responsible for the above phases of the design, if the desired process operation is to be obtained. In addition t o working with the other project design engineers, the instrument engineer must also work with the client to determine the extent to which the instrumentation will be affected by the operation and maintenance procedures that will be used after the process has been put into operation. For example: the client in many cases must be relied upon to establish the number of operating personnel that will be used on the process, as this may have an effect on the extent of automatic control. In addition, the availability and qualifications of the maintenance men may affect the type and construction of the instruments selected. Finally, the engineer must be able to aid the drafting department in the preparation of the installation drawings which will be required by the construction forces. I n view of these requirements the basic qualifications for an instrument engineer engaged in industrial design appear to be a general rather than specialized engineering background and a more than average ability to work with others,
Design The instrument design work on any industrial plant project may be divided into “preliminary design” and “production design.” The term “preliminary design” refers to that work which must be done to establish the scope of the project and thus make it possible to prepare a preliminary cost estimate for the job. This estimate is one of the primary factors used by the client in determining whether or not it is desirable to proceed further with the project. ‘(Production design” includes the work done from the time of approval of the preliminary design by the client until the design of the plant is completed. Before the actual work required of the instrument engineer can be divided into these two major divisions, consideration must be given to the type of preliminary estimate that is t o be prepared. For example, the cost of instrumentation may be
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INDUSTRIAL AND ENGINEERING CHEMISTRY
ohtained by estimating it as a percentage of the process equipment costs. In this case there is, for all practical purposes, no preliminary engineering involved. On the other hand, a detailed preliminary estimate may be required and therefore an appreciable amount of preliminary engineering must be done. It is important that the instrument engineer recognize these facts, since by doing so he is able, for a given project, to set limits on the amount of detail to be furnished in the preliminary design stage, thereby minimizing the engineering costs for this work. In the following discussion the work required of the instrument engineer during preliminary +lid production design is covered. It has been assumed that a detailed preliminary estimate is to be prepared for the project.
Preliminary Design As previously mentioned, this stage of the design covers the preparation of the preliminary estimate. Since a detailed estimate is to be furnished, preliminary specifications covering the instruments must be prepared and estimates of the piping and electrical materials required for the instrumentation must be made. I n addition, an estimate must be made of the production engineering required should the client decide to proceed with the actual design of the plant. A description of the work covered by the estimate must also be furnished. In order to undertake the preliminary engineering, the following information must, in general, be available: 1. Process Flow Sheets: The preliminary cheniical or process flow sheets which show, functionally, the process equipment and piping; usually the flow of process materials, and the allowable variation in process variables are shoxn on these sheets. 2. RIaterial Balances: These include the preliminary material and energy balances covering the utilities and any special services. 3. Plot and Equipment Arrangement Plans: The preliminary drawings showing the location of buildings and the layout of equipment in the various buildings.
Preliminary Specifications. The first step in the preliminary engineering, following a review of the process, is the preparation of the preliminary specifications covering the instruments, the instrument panels, and the equipment required for the supply of controller operating medium. Since these specifications are primarily used as a source of information for obtaining prices, the amount of detail is minimized. Tsually, the specifications are not put in formal form but appear only as notes on the engineer’s work sheets. The actual development of the specifications takes place in two steps: The first consists of a process analysis to determine the variables that must be metered or controlled; the second consists of selecting the specific instruments that are required to satisfy the analysis. I n order to proceed with the process analysis, the engineer must have available the process flow sheets and the material balances. The analysis is usually undertaken by first going through the process stepwise to select those variables which when controlled will permit the unit to operate as close to design conditions-i.e., output rate and product quality-as possible. Following this, the procedure is repeated to determine those variables which require metering as an operational aid or for accounting purposes. The selection of the specific instruments to satisfy the above analysis will depend on a number of factors involving the process conditions, the physical characteristics of the plant and equipment, and the design of the instrument itself. Giving consideration to these factors will require discussions with the process, mechanical, and electrical design engineers. In addition to these factors, the client’s intended operating procedures and maintenance program may also have an effect on the instruments selected. However, in the preliminary stage, the effects of these factors are seldom given consideration except in establishing the size and location of the major operating panels
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and satisfying requests from the client to consider specific types or manufacture of instruments. In general, the following information, where applicable, will sufficiently specify the instruments to permit preliminary costs to be obtained and a preliminary description to be prepared. 1. AIeasuring Element: The type of primary element to he used such as thermocouple, orifice plate, etc., must be determined. 2. Type of Control: Keeds to he determined to the extent of whether the control device is to be self- or relay-operated. If the latter is used, then operating medium must be specified. 3. Instrument Type: I t must be decided whether a directconnected or remote transmission type instrument is to he used. If the latter type is decided on, then the location of the control mechanism should be fixed so that piping runs can be more accurately determined. 4. Instrument Mounting: I t niust be decided whether the instrument is to be local or panel mounted. 5 . Instrument Display: Recorders requiring electric clock drives must be designated for electrical purposes. 6. Special: Any unique features of the instrument, such as requiring an explosion-proof housing or containing parts of an alarin or equipment interlock system should be established.
Khen the specifications for instruments have been completed, sketches are made of the panels that will be required. These are normally roughed out on sketch paper to determine the approximate over-all dimensions. On completion of the instrument specifications, the number of ielay-operated controllers can also be determined and an estimate made of the operating medium requirements. Following this the equipment necessary to supply the operating medium can be selected. For air, which is probably the most widely used medium for process work, this equipment will consist of a compressor, with the necessary controls, receiver, dryer, oil filter, and a pressure regulating station. The type of equipment used will depend primarily on the capacity required. For small systems, a receiver-mounted compressor with an in-the-line dryer may be sufficient, whereas for larger systems the receiver will probably be a separate vessel and the dryer of the dual-ton er type. Piping Materials. For preliminary piirposes, the instrument piping is estimated in terms of the number of straight feet of pipe required. Consideration need not be given to fittings, valves, and supports, because the cost of the piping will be established by using a unit installed cost figure. Since the instrument piping at panels is usually included in the estimate for the panel it need not be considered at this time. The usual procedure in making an estimate of the piping is to spot the instruments on the preliminary equipment layout drawings and, then, after selecting a location for the air supply equipment to approximate the length of the distributing headers and the piping required for each instrument. I n locating t h o v instruments, which are installed in pipelines, it is of course necessary for the engineer to estimate the probable location of the process and utility piping. A take-off of quantities will be required for each of the following services: I . Supply Air: This includes the distribution headers plus the lines to controllers, valves, positioners, etc. 2. Signal Air: The piping beheen controllers and the control elements, from transmitters to receivers, etc. 3. Process and Utility Materials: The metering lines between the process equipment and piping and the instruments. In addition to determining the length, it is also necessary to determine the type of pipe required for the various services since the installed cost may vary appreciably depending on thr material used. For air, steel pipe, brass pipe, or copper tubing is used for the headers, but copper tubing is normally used for all other air lines. In general, the metering lines are considered to he of the same material and suitable for the same working pressures as the process or utility piping to which it connects.
INDUSTRIAL AND ENGINEERIYG CHEMISTRY
December 1951
Although this discussion on piping has assumed air to be the operating medium, it is, in general, applicable to any of the fluids normally used. Electrical Materials. The estimate covering the electrical wiring required for instrumentation is usually furnished by the electrical designer based on data furnished him by the instrument engineer. The estimate, although designated as electrical wiring, includes any electrical equipment, such as transformers and switches, which should be charged to instrumentation, since in most cases these constitute a very small part of the total electrical instrumentation cost. -Material
A. Instruments
$
B. Instrument Piping
C. Instrument Wiring Subtotal D. Contingency E. Engineering Expense Total Cost Figure 1.
Estimated Cost Labor
Total
--
$
$
--
---
--
Summary Form for Preliminary Instrument Estimate
The information required for the electrical estimate is transmitted through sketches, marked-up preliminary equipment layout drawings, and discussions between the imtrument and electrical engineers. It must be complete enough to determine the approximate requirements for: 1. Power wiring for controller operating medium, chart drives, and valve operators. 2. Signal wiring between controller and control element, from transmitters to receivers, etc. 3. Special wiring for thermocouple instruments, p H measurement, etc., if involved in any quantity.
In the preliminary stage the electrical requirements for panel lighting and for interlock and alarm systems are not usually considered as individual items, but allowance is made for them in the estimate. Wiring at instrument panels is, in most cases, included in the cost of the panels Preliminary Estimate. On completion of the preliminary engineering, the preliminary estimate is prepared. Figure 1 shows a typical form used to transmit the instrumentation costs for assembly into the total estimate for the project. Item A (Instruments) includes all instruments (meters, valves, etc.) and the instrument panels. The major equipment required for controller operating media, such as pumps, compressors, dryers, and coolers are not usually included in this item, but appear with the process equipment. The material cost for the instruments is based on the preliminary specifications and is obtained by using average manufacturers’ prices. The instrument labor, which covers mounting and installing the instruments, is o b t a i n 4 by using unit installation costs for the major items and adding a percentage of this for minor equipment. The cost of the panels is usually estimated by applying a priceper-square-foot figure, which includes the fabrication and installation of the panel and the installation of all piping and wiring at the panel. The breakdown of material and labor is estimated on a percentage basis in the case of field-assembled units, but for shop-assembled units the cost of the assembled panel is indicated as material and the cost of setting the panel as field labor. Item B (Instrument Piping) includes pipe, fittings, valves, insulation, and supports. The total piping cost is obtained by using an installed pri;e-per-foot figure. This is usually done by type of service, since, as previously mentioned, the unit installed cost may vary appreciably with the material and service conditions. The breakdown of the total cost into labor and material is obtained on a percentage basis.
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Item C (Instrument Wiring) covers all wire, conduit, etc., required to complete the electrical-instrument installations. I n general, this is a difficult item to determine accurately unless a detailed procedure of estimating is used. Since such a procedure is not normally warranted for preliminary estimates, the total costs for this item are usually estimated as a percentage of the cost of the instruments involved. Allowance is made for interlocking and alarm circuits by adjustment of the ratio used. The material and labor costs are determined on a percentage basis. The sum of items A, B, and C represents the total physical cost of the instrumentation. To this must be added the contingency and the engineering costs which would be involved should the actual design be undertaken. The contingency, as indicated, is established as a percentage of the total physical cost and for preliminary estimates of the type described, it is of the order of 10 to 15%. The engineering expense, item E, is the engineering and drafting payrolls which would be required to cover the production design. These costs are usually estimated by establishing the man-hours required for preparation of specifications and the square feet of drawings required. This item will include the home office overhead, which, for a given project, will be a fixed percentage of the payroll for engineering and design. In conjunction with the estimate, a deseription of the work that is included must be prepared. Usually this consists of indicating the instruments and instrument piping on the engineering flow sheets prepared for the project and preparing a written description of the instrument panels and controller operating medium equipment. I n some instances a preliminary list which gives, for the major instruments, (1) the equipment number, (2) service, and (3) type may also be requested by the client.
Production Design The production design begins when the client decides to proceed with the actual design and construction of the plant. The work done during this stage will include the preparation of (1) engineering specifications for procurement of the necessary equipment and materials; (2) instructions which will enable the field to install the instrumentation in accordance with the planned design; and (3) an official estimate to establish the contractor’s fee. During this stage of the design, the client frequently requests changes in the scope of the work and these, of course, must be included in the final design. Generally, this requires some preliminary design work on the part of the process involved. Although these items constitute the greater part of the engineer’s work he may also be required t o make bid comparisons, search for instruments to do special jobs, and prepare relative cost estimates if required for the selection of instrumentation equipment. I n discussing the duties of the instrument engineer during this stage of the design, the preparation of the following will be considered: job work sheets, specifications, field instructions, and h a 1 estimate. Before undertaking the final design, the engineer should have in final form (1) the process flow sheets, (2) the material balances, and (3) the preliminary engineering flow sheets. As the engineering progresses, copies of the mechanical drawings (including equipment plans and elevations and those made for fabrication of tanks and other process equipment) and the piping drawings will be required for working purposes. Electrical drawings are usually required for reference only. Copies of manufacturer’s equipment drawings covering process equipment designed by the manufacturer and involved in the instrumentation may also be required. Job Work Sheets. The instrument engineer must integrate his work not only with that of the other designers on the job, so that good instrumentation results, but alsowith the purchasing depart-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2114
ment, so that construct,ion schedules are met. Because of the great number of equipment pieces usually involved in instrumentation and the large amount of detail that must be handled in preparing the field instructions, it becomes necessary for the engineer t o set up job work sheets if he is to comply with the above requirements in an efficient and complete manner. Practice has indicated that best results are obtained if tiyo work sheets are used, one for correlating the inst,rumentation with regard to scheduling or purchasing, the other with regard to the design. An instrxnient list (Figure 2) is a form normally used by the engineer in connection with scheduling or purchasing to ensure that the delivery of equipment to the field nil1 meet the requirements of the construction forces. The first four columns to t'he left, including (A), are used to identify the instrument. This identification is important since it will be used throughout all phases of the design, purchase, and construction. Columns B to H cover those items which must be considered in scheduling the order in which specifications are to be written. These data are also useful to the engineer in discussions lvith the purchasing and construction departments. Columns J to M relate to manufacturer's drawings and instructions, which are furnished for the instruments, and form an index which permits the engineer to account for these items. In normal usage the identification columns are filled in first. Following this, the required delivery of all instruments (column G) is established using the job construction schedule. When this has been done, the required date for the requisition, the quotation, and finally that for the specification is established. Columns J to h/I are normally filled in with a date for reference purposes. The Instrument' Design Work Sheet (Figure 3) serves as an aid to the engineer in correlating his work with that of the mechanical and electrical design groups and as a check list of the information required by the field forces. The first four columns on the left are the identification information required on each instrument. Columns B to E relate t o the specifications and give the number, the date originated, the date it went to the client, and the dat'e the client approved it,. Columns F to M refer to the various drawings, mechanical and electrical, on which the installation details covering the instruments and their components are shown. These items are of particular value as an aid to the engineer in connection with the preparation of the construction drawings covering the instrumentation. Columns N and P refer to the memorandums which are often written to transmit information to the other design engineers and draftsmen in connection with instrument piping and electrical work. R is used to indicate the type povier, such as air or electricity, that may be required for various instruments. The value of this work sheet will become more apparent following the discussion of the design work. Specifications. As previously ment,ioned, t,he purpose of the engineering specification is t o transmit to the purchasing department the information necessary for procurement of t'he materials required for the plant instrumentation. I n addition to serving this purpose, the specification also forms the basis for the preparation of field instructions and, in the case of the instrument equipment, gives an engineering record of the operating and design conditions. This record may prove of particular value if, aft,er
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initial operations, it becomes desirable t o make modifications in the process. In addition to preparing the instrument specifications, the instrument engineer is usually required to furnish the specifications for the controller operating medium supply equipment and the instrument piping not covered by process piping specifications. The specifications for electrical wiring, conduit, etc , are furnished by the electrical design engineer, hou-ever, the material specifications for special wire such as that used for thermocouples and in pH measurement, are usually prepared by the instrument engineer. The preparation of the final instrument specification begins with a review of the preliminary specification. If the process conditions have not been altered and the client has not requested changes in the instrument, the neceksary detail is added to put the specification in final form. Should the instrument selected no longer be satisfactory, then, the preliminary engineering must be repeated. I n converting the specification from preliminary to final form, the engineer must apply the principles of instrument engineering, in so far as measurement and control are concerned and, a t the same time. give due consideration to the effects on the selection of the instrument of (1) the process conditions, (2) the physical characteristics of the plant and equipment, (3) the operating procedures to be followed, and (4) the client's maintenance program. I n order t o satisfy these requirements, the instrument engineer must integrate his work with that of the other job engiwers. The effect of procees conditions and operating procedures on the selection of instruments is determined through use of the process flow sheets and discussions with the process engineer and the client. I n this manner the materials of construction to be used for metering and control elements, the type of control mechanisms required, the location and layout of instrument panels, the location of locally mounted instruments, and other similar items are established. Consideration of the client's maintenance procedures may result in the selection of a particular type or manufacture of instrument, I n addition to working with the process engineer, the instrument engineer must also correlate his work with that of the mechanical designer responsible for the process equipment and piping. For tanks, dryers, and other process equipment, all required connections must be properly located so that the metering and controlling functions are served as Fell as the mechanical design. In connection nith pumps, fans, etc., the pressure drop through in-the-line measuring and control elements must be established so that the head required for the pumping equipmrnt can be determined and, for control elements, sufficient drop I S available t o permit the element to function properly. If an orifice or similar meamring device is t o be used and it is necessary t o provide a special metering run, then, such information must be furnished t o the piping designer. These examples are typical of
1 Figure 2 I
Figure3
t
.
December 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
which apply to the particular panel under consideration. The written part covers the materials to be used and the methods that are to be followed in fabricating the panel and installing the piping and wiring. The drawings furnished may vary depending on whether the panel is to be field- or I 61 shop-assembled. If assembly is t o be done in the ETfX CONSTRUCTION field, then two layout drawings-one showing the 7 Ufr. k Model No. 8 Thermal system arrangement of equipment on the panel and the 9 Indicator or Recorder other the installation of the piping and wiring be10 Range hind the panel-and a cutout drawing showing in 11 Case Construction I complete detail the openings required in the panel 12 I Mounting .I I I are usually prepared. When the panel is to be 1 F l e x i b l e TubinR shop-assembled, the design engineer usually fur14 I l l a t e r i a i I I I nishes only the cutout drawing, the others being 15 I Connection ~6 I Lsngth. i t ! I I furnished by the vendor. Since instrument piping is required for metering 17 Meterial Were11 LBnuth, i n . 18 lines and for controller operating and signaling Connection 19 mediums, specifications must be made available Elevetion from c a s e , tt 20 S e w r a b l e Socket for each of these services. Usually, the piping for 0verall Le nRth I I 31 metering lines is identical with the process piping 22 Material Lagging Extension. i n . 23 to which the lines are connected, and therefore, the External oomection 2El Indicator Dial necessary specifications will be furnished by the piping designer. ‘Generally, air is used as the con2b Chart S i n e 27 Chart D r i v e ( 1 ) troller operating medium and copper tubing is 28 nD..Of Pens used to supply air to the controller and for trans29 Accessories mission of controller signals. Since this type of service is not normally met in general process work the preparation of these specifications is (1)Supply f o r e l e c t r i c drive to be 110 V , 60 c y c l e s usually the responsibility of the instrument engi* The bidder i s t o furnish in his r r m ~ o s a la l l items ;oerked with an.aeterisk neer. In practice, general specifications are set up ~ Issue NO. _ DBte_ _ Changes RalesrsdEoe-for this service and therefore the engineer need only ~ modify these general specifications for the particu-~ ~ _ _ _ _ _ _ lar project under consideration. Where other PROJECT T I T L E 0. (1 2 PROJECT NO operating mediums are used and specifications CLIENT CLIENT PROJCOT NO are not available, the instrument engineer must LOCATION S P E C I F I G AT1 O N work with the piping designer to establish the TEMPERATURE. IN 0 1 c A T O R / R E C O R O E R required specifications. Specifications required for electrical wiring and PRESSURE ACTUATFD SYSTEMS accessories are furnished by the electrical deEOUlP NOS signer. The instrument engineer usually furnishes D A Y (L Z I Y N C R Y A H N , INC , ENGINEERS. PHILL , PA SHEET-OFmaterial specifications on thermocouple or other Figure 4 special wire, but beyond that he does not become involved in the preparation of electrical specifications. Field Instructions. Regardless of how well the instrumentathe problems that must be solved through coordination with the tion design is accomplished, the results obtained in operation will mechanical group. be no better than the installation of the various components. During the preparation of the final specificationb, coordination For this reason, the instrument engineer must prepare the design with the electrical designer is required in conjunction with those data in such form that the field can make proper installations. instruments which function as part of an equipment interlock or The primary method of transmitting the design data t o the alarm circuit. Before proceeding with these specifications, a field is through mechanical and electrical drawings, including memorandum covering the interlocking and alarm circuits is those prepared by the design engineers and those furnished by usually prepared by the instrument and process engineers. The the instrument manufacturers. I n addition, memorandums and description of the circuits is functional only-Le., it tells what manufacturers’ installation instructions are used to supplement, the circuit is to accomplish from an operating standpoint. Using the data given on the drawings. Copies of the instrument list this memorandum as a basis, the instrument and electrical engineers must agree on the instruments to be used and the circuit and the instrument design work sheet are also given to the field since they serve as an index to the drawings, thereby permitting arrangements. the field to operate more efficiently. In preparing specifications for the more commonly used instruThe drawings used to correlate the instrumentation data m a l ments, standardized forms, similar to that shown in Figure 4, are vary widely depending on the project under consideration and normally used. The use of such standards will appreciably reduce engineering costp. the client. However, regardless of the type and number of Preparation of specifications for the controller supply medium drawings prepared, they must, in general, include the following equipment and accessories, will, in general, involve working with information : the process engineer and client to the extent of establishing the 1. The type and location of all metering connections and the additional capacity that should be allowed for future requirelocation and mmnting details for all in-the-line metering and conments and the type of power to be used for the drive trol devices The final specifications for the instrument panels usually con2. The location and support details of all locally mounted sist of a written specification of a general nature and drawings equipment
*
-~ ~~
c1
x
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Vol. 43, No. 12
-4s an alternate to the individual standards and rvhen standards are not available, special drawings similar information - are made which give but with t,he details shown for each manufacturer's instrument,. Drawings of this type have the advantage that each connection is shown F L A R E D ADAP TER in its exact relative position and is ident,ified with the actual marking on the instrument. The information required for items 4 and 6 i p CONTROLLED AIR F L A R E D ADAPTER furnished by electrical drawings consisting of schematic wiring diagrams, det'ailed airing diaCOMBINATION FILTER grams, and conduit layout drawings. Thc inREDUCING VALVE C L E A R A N C E ILEP'D. OP FILTER REMOVAL formation required for the preparation of these NIPPLE drawings is normally transmitt>ed t o thtl electrical designer through manufacturer?' drawings, LEVEL CONTROLLER WITH interlock circuit memorandums writt,cv for the preparation of specificatioiis, and thc instrummt H I G H /LOW LEVEL SWITCH design work sheet, Figure 5 The drawings uscd to describe t'he instmnient piping (item 6) should sholv the location of the line; indicate the line number, service, size, and 3. Details of the piping and electrical connections a t each fabrication specification; and indicat,e the supports reqiiircd. instrument The type drair-ings used in conjunrtion lvith the instrument pip4. The details of the wring a t each instrument ing vary widely depending on the size of the project and the 5 . The layout of the instrument piping including metering lines and operating medium supply and signal lines amount of detail required. For large projects complete drawings 6. The layout of conduit for instrument wiring including plans and elevations may be prepared, whereas for s m a k r projects the instrument lines may be shown ~atisfactorily I n addition t o this information, the assembly and mounting deon the process piping drawings. X method which is oft,en used, tails for the panels must be furnished. The assembly details and one which is useful on almost any size project, consibts of will be shown, as previously mentioned, on layout drawings preshoxkig the instrument piping on rcproductions of the equipment pared for the specification, and the method of mounting the layout plans. Since elevations of instrument piping are seldom panels is normally shown on the job stri~cturaldrawings. necessary, this type drawing meets the field requirenirnts and, I n transmitting these data t o the field, use is normally made of in addition, is probably the most economical t o preparc (1) equipment and piping dra,.sings; (2) electrical dravr-ings; (3) Final Estimate. During the production engineering stagc, an instrument piping drawings; and (4) special instrument drawings. official estimate must be prepared to establish the engineering The informat ion required for items 1 and 2 is given on the procfee and the client's commitments. Vsually, by the time this ess equipment and piping drawings. The details for metering estimate is made, the design dl have advanced to the point connections located on process equipment, as previously menwhere the major instruments have been selected and it is possible tioned, are shon-n on the drawings made for fabrication purposes. to make accurate take-offs of piping and wiring. The final The location and mounting details for in-the-line metering and estimate will differ from the preliminary estiniat,ein that it ~villbe control devices and the location and dctails for supporting locally more accurate and will include the cost of changes in the scope of mounted instrument's are usually shon.n on the piping dra'ivings Jvork. for the services involved. Often, nhere there is a large number of locally mounted instruments, the location of the instrument is Concclnsion shown on the piping draviing and a special draiving is prepared to r. 1 hroughout this papw tho instrument ctngineer has been reshow in detail the supports required. The location of the operatfcrred to as though he n-erc one individual. Actually, in large ing medium supply equipment and the operating panels is shown organizations, the instrument wgineering may be handled by a on the equipment layout dralvings. Since the preparation of the group of engirieere, each specializing in some particular phase of equipment and piping drawings is the responsibility of other the dcsign work I n addition: the scope of the work covcrcd by designers, the instrument enginwr must supply the necessary instrument engineering niny vary Tr-idely, drpending on the data t o those responsible. This is normally done by means of organizat ion. sketches, manufacturrrs' dran-ings, and marked-up copies of the The author realizes that this paper is far from being a complete drawings involved. discussion of the functions of the instrument, engineer in process The details of the piping and electrical connections at locally design, hut hopes that the information presented will stiniulate mounted instruments, item 3, are normally shown by the use of similar articles by othws. installation standards similar t'o that shown in Figure 5, These BRAIS
NIPPLBJ
(SHORT A I POJIIBLE)
standards are prepared for t,he more commonly used instruments.
RECEIVED May 1,1951
nd s f Pnstrumentation Symposium
