Instrumentation Diagrams, Documents and Checklist

For a successful completion and the afterwards maintenance of plant instrumentation, the following drawings and documents are required. These documents serves its purpose right from the designing of the plant to erection, commissioning and successful running of plant. The documents are further used for maintenance of the same.

There are basically 2 drawings, more than 23 documents and more than 7 check lists used for instrumentation documentation. A brief explanation is as follows:

The 2 basic drawings are

1. P&ID

2. PFD

The 16 basic documents used for designing and constructions are

1.Piping details of instruments

2.Installation schedule of instruments

3.Calculation sheets for instruments

4.Specification sheets for instruments

5.Cause and effect diagrams of instruments

6.Layout drawings

7.Interconnection wiring diagrams of instruments

8.Process system drawings for equipments

9.Segment diagrams of instruments / GA drawings

10.Special drawings

11.Architect diagram or System block diagram

12.Logic diagrams

13.Emergency shutdown system functional diagram

14.Mounting details/Hook up diagram

15.Decommissioning documents

16.Cable schedule

17.I/O List

18.Vendor list and drawings

19.Instrumentation index

20.Loop drawings

21.JB Schedule

22.Concept node/ Control narrative



Apart from these documents there are various check lists for instrumentation. These includes


2.Punch point list.

3.Inspection report

4.Loop check list.

5.Logic checklist.

6.Process graphics checklist.

7.Installation checklist

8.Calibration check list.


A brief explanation of diagram can be given as follows:


The instrumentation department of an engineering firm is responsible for the selection of field devices that best matches the process design requirements. This includes the selection of the transmitters that fit the operating conditions, the type and sizing of valves, and other implementation details. An instrumentation engineer selects field devices that are designed to work under the normal operating conditions specified in the process flow diagram. Tag numbers are assigned to the field devices so they may be easily identified when ordering and shipping, as well as installing in the plant. The decisions that are made concerning field instrumentation, the assignment of device tags, and piping details are documented using a piping and instrumentation diagram (P&ID). A piping and instrumentation diagram is similar to a process flow diagram in that it includes an illustration of the major equipment. However, the P&ID includes much more detail about the piping associated with the process, to include manually operated blocking valves. It shows the field instrumentation that will be wired into the control system, as well as local pressure, temperature, or level gauges that may be viewed in the field but are not brought into the control system.

As mentioned earlier, the engineering company that is creating the P&ID normally has standards that they follow in the creation of this document. In some cases, the drawing includes an overview of the closed loop and manual control, calculations, and measurements that will be implemented in the control system. However, details on the implementation of these functions within the control system are not shown on the P&ID. Even so, the P&ID contains a significant amount of information and in printed form normally consists of many D size drawings (22 x 34 inches; 559 x 864 mm) or the European equivalent C1 (648 x 917mm). The drawings that make up the P&ID are normally organized by process area, with one or more sheets dedicated to the equipment, instrumentation, and piping for one process area.

Piping and Instrumentation Diagram is drawing that shows the instrumentation and piping details for plant equipment. The P&ID acts as a directory to all field instrumentation and control that will be installed on a process and thus is a key document to the control engineer. Since the instrument tag (tag number) assigned to field devices is shown on this document, the instrument tag associated with, for example, a measurement device or actuator of interest may be quickly found. Also, based on the instrument tags, it is possible to quickly identify the instrumentation and control associated with a piece of equipment. For example, a plant operator may report to maintenance that a valve on a piece of equipment is not functioning correctly. By going to the P&ID the maintenance person can quickly identify the tag assigned to the valve and also learn how the valve is used in the control of the process. Thus, the P&ID plays an important role in the design, installation and day to day maintenance of the control system. It is a key piece of information in terms of understanding what is currently being used in the plant for process control.



To meet market demands, a company may commission an engineering firm to build a new plant or to modify an existing plant to manufacture a product that meets certain specifications and that can be manufactured at a specific cost. Given these basic objectives, a process engineer will select the type of chemical or mechanical processing that best meets the planned production, quality, and efficiency targets. For example, if the equipment is to be used to make more than one product then the process engineer may recommend a batch process. For example, a batch reactor may be used to manufacture various grades of a lubrication additive. Once these basic decisions are made, the process engineer selects the equipment that will most cost-effectively meet the company’s objectives. Based on the production rate, the process engineer selects the size of the processing equipment and determines the necessary connections between the pieces of equipment. The process engineer then documents the design in a process flow diagram (PFD). The process flow diagram typically identifies the major pieces of equipment, the flow paths through the process, and the design operating conditions—that is, the flow rates, pressures, and temperatures at normal operating conditions and the target production rate.

Process flow diagram – Drawing that shows the general process flow between major pieces of equipment of a plant and the expected operating conditions at the target production rate.

pfd 2pfd

A brief explanation of documents can be given as follows:

1.Piping details of instruments

Instrument piping details are generated from SPI hook up module functionality. These gives  details of instruments installed in an equipment or in a pipe.

piping detail2piping details

2.Installation schedule of instruments

These documents are used as the primary instrumentation index and are prepared from SPI software. The time schedule for starting and finishing of a work is graphically said in these diagrams.

instrument schedule

3.Calculation sheets for instruments

These forms can be generated from SPI standard calculation module. The below form gives us details regarding the calculation done to select a particular instrument for a particular process with respect to pipe size, process, area and its application.

calculation sheet

4.Specification sheets for instruments

These forms can be prepared from SPI standard specification sheet module. This document has details regarding instruments tag number, service, P&ID number, make, model, serial number, lower sensor limit, upper sensor limit, material connections, power supply types etc.

specification sheet for instrumentsinstrumentation specification sheet 2

5.Cause and effect diagrams of instruments

A cause and effect drawing is a chart showing ESD or regulatory control system output reaction in response to abnormal input changes, giving details of process alarms, or trip points in response to process parameters or operating conditions. It is required for all permitted modes of plant operation. This does not detail all the logic decisions which takes place and cannot replace the logic diagram. It is arranged in a way that abnormal process conditions result in either shutdown or isolation of process equipments. For instance, if HH level of KO drum is sensed then shut down the compressor drive and close the isolation valve.

cause and effect 2cause and effect3

6.Layout drawings

Control room layout drawings show in plan views, the location of consoles, panels, control racks, computer racks and peripherals, logic racks, termination racks and boxes. Remote building layout drawings show the position of each item of major equipment like process interface building, analyzer house etc. Layout of control room console, panels, cabinets, or local panel serves as a guide for construction but does not provide exact dimensions. Only the overall dimensions, location of instrument items, shape, graphic layout, and general layout are provided in this. Front and back of cabinet/rack layout show dimensions, equipment location, wiring raceway, cable entries and terminal strips.

layout diagram

7.Interconnection wiring diagrams of instruments

Instrument interconnection wiring diagram are prepared for junction box and field control panels, Marshelling cabinets and instrument console/panels, cabinet/racks, junction boxes located in process interface building, substation, control rooms etc.

The main purpose of this drawing is to the individual wiring between devices and to identify the cable numbers, wire tagging, terminal identification, fuses sizes etc. All spare termination details are also shown in these drawings. Some simple wiring diagram are as shown below

wiring diawiring dia 3

8.Process system drawings for equipment

These drawings consists of the control system for opening of closing of valves for controlling level, pressure, temperature, flow and quality of any vessel or system on a large scale. This will have narrative explaining the control of system along with its logic. This is accompanied by control application program related documents. These documents also include smaller scale process system drawings such as analyzer unit. These are generally drawings relate to a system operating in plant like steam and water analysis system drawing as in analyzer panel, TIC- TOC (Total organic content/Total inorganic content) analyzer panel system, water in oil and oil in water analyzer panel etc on a smaller scale.

system drawings

9.Segment diagrams of instruments / General arrangement (GA) drawings

These drawing give us details regarding the cross sectional, top, front and side view of instruments along with its fittings like SS, ground terminals or conduits, HP, LP side in case of DP transmitter, mounting bracket details.


10.Special drawings

When intrinsically safety is used for protection in hazardous areas a special drawings like system control drawings are made in which both the intrinsically safe apparatus and the associated apparatus are identified by the manufactures, model numbers and entity parameters. Some special drawings are Bentley Nevada VMS drawings, Woodward governor documents, IR compressor module packages etc, BMS for boiler management.


11.Architect diagram or System block diagram

These drawings will be having a block diagram format of all major control systems components including routers, switches, gateways, servers, subsystems etc. Some of these drawing also identifies where all these physical components are located in CCR, Substation, Utilities control building. The overall cable wiring details are also provided along with the cable types, speed of communication link, protocol type and redundancy in some of the block diagrams but not every block diagrams. These drawings are generally drawn showing the DCS architecture, including all connected auxiliary systems like PCS, ESD, VMS, Compressor control, F&G, Printers etc.

system block diagram 2system block diagram

12.Logic diagrams

For a PLC or programmable logic controller to work, it must be programmed to do so. The most popular language used for programming a PLC is ladder logic. A simple ladder logic diagram is as shown below.

ladder logic

13.Emergency shutdown system drawing

Details of ESD drawing consist of following documents also contains Cause and effect supporting ESD actions, logic diagrams of ESD control narrative etc. The figure below shows an ESD drawing implemented using functional block diagram. ESD system is to shut down a unit or plant in case of any abnormality occurs in plant which would otherwise cause casualty or accident in a plant or factory.

esd fun dia2esd fun diagr

14.Mounting details/Hook up diagrams

These are also similar to piping details of instrument documents. In piping details, we get piping related documents for instrument locations and mounting styles. In mounting details there is wide perspective of installation techniques involving impulse tubes, mounting brackets, stanchions, flanges, capillary tube, nut-bolts, canopy, equalizing valves etc. These drawings can be generated from SPI hook up module functionality. A hook up diagram format is as shown below

hookup 1hookup 2

15.Decommissioning documents

Decommissioning activities is a very vast topic to be covered. It is beyond the scope of this article. A decommission documents include site evaluation documents; closure considerations like decontamination, waste disposal, soil removal etc; closure tasks and programmes; closure plan validation; closure plan costing etc. Some sample document is as shown below

decom 1decom 2decom 3decom 4decom 5

16.Cable schedule

The cable schedule documents give us a detailed explanation of the cable for laying. For instance PCS signals uses paired cables, ESD signals uses core cables, and FNG uses triad cables. These details along with cable number, cable type, drum number, cable length, vendor, details for cable laying regarding source panel to destination panel are also specified. Some sample cable schedule list as shown below

cable list list report 1cable list list report

17.I/O List

The Input output list gives explanation of the inputs and outputs of ESD, PCS and FNG groups. It gives us details about inputs like PT, FT, LT tag details and outputs like Control valve tag, On/Off valve tags etc. The details included in the I/O list are PID number, loop number, tag number of I/O service, location, type of function whether ESD, PCS or FNG, I/O type whether digital or analog, range, unit, redundancy, category etc. Some sample I/O lists format are as shown below.

I-O list 1I-O list

18.Vendor list and drawings

These lists consist of the vendors who supply the instruments to the client. These vendors provide their instrument details and related documents and drawings which are known to be vendor drawings. The total number of vendors, who are allowed to supply instruments in the project are listed in vendor list and their manuals are considered as vendor drawings. Some sample vendor lists for instrument supply are as shown below

vendor list 1vendor list 2vendor list 3

These authorised vendors are thereby needed to provide the vendor drawings related to their instrument details of each tags and its installation method and its datasheets. A sample vendor drawing for a pressure gauge is as shown below and its specification

vendor drawing 1vendor drawing 2

19.Instrumentation index

An instrument index gives us the total instruments to be installed in a project. It gives us the details regarding the instruments like tag number, instrument type like Pressure transmitter, FT or LT etc, P&ID number, equipment number, scope, location, I/O type, system, category etc. A simple instrument index format is as shown below.

instrument index

20.Loop drawings

The piping and instrumentation diagram identifies, but does not describe in detail, the field instrumentation that is used by the process control system, as well as field devices such as manual blocking valves that are needed in plant operations. Many of the installation details associated with field instrumentation, such as the field devices, measurement elements, wiring, junction block termination, and other installation details are documented using a loop diagram. A loop diagram, also commonly known as a loop sheet, is created for each field device that has been given a unique tag number. The loop diagrams for a process area are normally bound into a book and are used to install and support checkout of newly

installed field devices. After plant commissioning, the loop Diagrams provide the wiring details that a maintenance person needs to find and troubleshoot wiring to the control system.

Loop Diagram – Drawing that shows field device installation details including wiring and the junction box (if one is used) that connects the field device to the control system. The loop diagram typically contains a significant amount of detail. For example, if a junction box is used as an intermediate wiring point, the loop diagram will contain information on the wiring junctions from the field device to the control system.As is illustrated in this example, junction box connections are shown on the line that shows the division between the field and the rack room. The loop diagram shows the termination numbers used in the junction box and the field device and for wiring to the control system input and output cards. Also, the Display and Schematic portions of the loop diagram provide information on how the field input and output are used in the control system.Also, connections are shown between the control system analog output card and an I/P transducer and pneumatic valve actuator. Details such as the 20 psi air supply to the I/P and the 60 psi air supply to the actuator are shown on this drawing. Based on information provided by the loop diagram, we know that the I/P will be calibrated to provide a 3–15 psi signal to the valve actuator. In addition, specific details are provided on the level measurement installation. Since the installation shows sensing lines to the top and bottom of the tank, it becomes clear that the tank is pressurized and that level will be sensed based on the differential pressure.Even fine details such as the manual valve to regulate the flow of purge water are included in the loop diagram to guide the installation and maintenance of the measurement device. The loop diagram provides information that is critical to the installation, checkout, and maintenance of field devices. By examining the loop diagram, it is possible to learn details that may not be obvious when you are touring the plant site. A simple loop drawing format is as shown below.

LOOP DIAGRloop diagram

21.JB Schedule

A JB schedule gives us a detailed description of termination and wiring to be carried out in a junction box. It gives us how is the primary cable coming from Marshelling cabinet is connected to field cables or secondary cables of the respective instruments. Normally the secondary cables are connected to the left side of the terminal block of JB and the primary cables are connected to the right side of the terminal block. A JB schedule details include the number of terminal strips, JB location, colour code of the cables, instrument tag numbers, polarity of the cables, shield cable connection details etc. A simple JB schedule is as shown below.

JB scedule

22.Concept node/ Control narrative

A Concept note explains the ESD logic shown in the logic diagram. This narrative serves as guideline for embedding comments in ladder and logic diagram networks. A process control narrative, or PCN, is a functional statement describing how device-mounted controls, panel mounted controls, PLCs, HMIs, and other processor-based process control system components should be configured and programmed to control and monitor a particular process, process area or facility. PCNs are sometimes referred to as concept node, control strategies, control narratives, sequence descriptions, and by other similar names. A PCN is the essential link between process design and control system design. It also forms an integral part of the final control system documentation, providing in the most concise but descriptive form, a statement that ties together process operation, process equipment, instrumentation, control philosophy, available control modes and control loops, as well as documenting control logic settings such as set points, computed values, alarm limits, normal operating limits, trips, interlocks, and other key parameters. A concept node is as shown below

control narrative 1control narrative 2control narrative 3control narrative 4control narrative 5control narrative 6control narrative 7control narrative 8

23. BOQ or Bill of Quantity.

BOQ or bill of quantity is the quantity or number or amount of materials need to carry out project. Normally 20% extra or spare is requested for carrying out the work in order to compensate for shortage. These BOQ includes number of JB, length of cables, number of instruments, number of instrument fittings, its installation and service cost, cable trays and ducts, canopy and sun shed, angles and plates, SS tubes and all materials related to erection of instruments. It consist of description of material to be purchased or procured, its quantity, its weight or unit, quantity to be procured within a time limit etc. Some simple form of BOQ are as shown below.


Now we will discuss about various check list used in instrumentation. There are more than 8 check lists for instrumentation. These includes


FAT or Factory acceptance test and SAT or Site Acceptance Test are one and same only. The only difference is FAT is executed at vendor test facilities and SAT is carried out at client site. FAT / SAT documents covers all the functional specifications of the equipment as demanded by the client requirements.

Factory Acceptance Tests are done at the factory to make sure that certain requirements are met, which results in high quality products. The tests are normally done with the customer, and also, in certain more demanding cases, with a third party inspection agency.

Although all cabins should be fault-free when they arrive from the subcontractors that assemble them, faults sometimes occur. Therefore these factory acceptance tests are needed.

At a FAT, installations are double checked so that they match the drawings for the specific project. Functions that should work when cabins are installed at site are also simulated to check the automation functionality. All possible faults, deviations and wishes are also noted.Site Acceptance Tests are done at the specific places where commissioning is done. These tests are also done to make sure that certain requirements and a high quality are met amongst client’s projects and to offer customers quality testing and documents. Normally the same test procedures as at FAT are followed, plus procedures that cannot be done at FAT. E.g. breaker control is excluded from FAT but done at SAT. The results of the SAT are noted in the test protocols and then signed by both the customer and the commissioner. A FAT/SAT procedure covers 6 main parts:


b.System Software,

c.Human Interface Station Application.

d.Field Control Station Application

e.Safety Control Station Application

f.Field Control Node Application.

These procedures are covered in detail in another topic SAT/FAT procedures and is beyond the scope of this article.

2.Punch point list.

This checklist covers instrument list whose works are to be completion after the erection phase. The list have date, item description, the person who have inspected, action plan for completion of work, whether the job is completed after the issue of punch list, comments regarding the punch list etc.

punch list

3.Inspection report.

The inspection check list is generally is filled by QA and QC instrument engineer to confirm whether individual tag number are installed properly. The list details about the tag number, model, serial number, inspection checks for correct tagging, leak test, wiring, cable tags etc. An inspection checklist for a switch is as shown below.


4.Loop check list.

These check list gives us details regarding each loop for transmitters used in an erection. These details about the type of signals like AO, DO, ESD, PCS, FNG etc. It also confirms transmitter display, output and include the results of hot and cold loops performed. These also do have continuity test report regarding the loop. Some loop check reports are as shown below.


5.Logic checklist.

This checklist gives us data regarding the logic checks performed during commissioning phase and include the details of logics implemented in a control system or start up of a system. These have details regarding instrument tags, its state, alarms, inputs and outputs, how many items are affected during its activation etc.


6.Process graphics checklist.

The HMI or a control station panel will be having graphics for human interface. These graphical icons are tested during commissioning and erection period tag wise. This is done and documented in process graphics tag list. This list has graphic tags, service, its static test result and its dynamic test results during its working. For example the red colour of a control valve indicate it is closed and green colour in its graphic represents closed and yellow colour represents the valve moving condition. These are verified and are documented in a process graphics list. A process graphics checklist is as shown below.


7.Installation check list:

The instrument installation check list is similar to inspection checklist and details whether an instrument is properly installed in a field. A simple installation check list is as shown below


8.Calibration check list

A calibration check list contains the details of calibration check done during its commissioning period for its proper working. The instruments are checked for their various ranges from 0% to its 100% in both increasing and decreasing order. These details include instrument tag, model number serial number, range, test ranges, equipments used for testing, performer and verifier signature etc. These check list is also used for annual maintenance report for carrying out preventive maintenance and corrective maintenance documentation. Simple calibration checklist is as shown below

calibration check listSUMMARY DOCUMENTS

6 thoughts on “Instrumentation Diagrams, Documents and Checklist

  1. The content material are Very Nice Sir,
    Now I can understand and relate to what it means to be , while working as an Instrumentation engineer .
    Thanks !!

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