The purpose of loop diagrams are to represent associated electrical and piping connections of a instrument loop.
Instrumentation Loop diagrams serve many purposes. Several of these stated below are in the chronology of project development.
The loop diagrams are helpful during the design stage as listed below.
1) Illustrate control philosophy and confirm the completeness of submitted data
2) An extension of P&IDs, which show the components and accessories of the instrument loop, connections between devices, and identification of component action
3) The specification of instrument hardware items and a means of communicating requirements to vendors.
The loop diagrams are helpful during the plant construction as listed below.
1) Panel instrumentation interconnections and checkout diagram
2) Instrumentation installation references and special requirements
3) Instrumentation interconnections
4) Instrumentation loop checkout
5) Inspection and documentation
The loop diagrams are helpful during the start-up as listed below.
1) Pre-start-up commissioning and calibration
2) Training tool and aid
The loop diagrams are helpful during the operation as listed below.
1) Communication medium between operations, maintenance, and engineering personnel
2) Training device for operations
The loop diagrams are helpful during the maintenance as listed below.
2) Routine calibration
3) Preventative and corrective maintenance tool
The loop diagrams are helpful during the modification as listed below.
The instrument loop diagram is a composite representation of instrument loop information. It contains all associated electrical and piping connections and should contain all of the information needed to accommodate the intended uses.
Classified below are minimum requirements and some established options that can be used to match the desired uses.
1) Identification of the loop and loop components shown on the P&IDs.
2) Word description of loop functions within the title. If not adequate, use a supplemental note. Identify any special features or functions of shutdown and safety circuits.
4) All point-to-point interconnections with identifying numbers or colors of electrical cables, conductors, pneumatic multi-tubes, and individual pneumatic and hydraulic tubing. This identification of interconnections includes junction boxes, terminals, bulkheads, ports, and grounding connections.
5) General location of devices such as field, panel, auxiliary equipment, rack, termination cabinet, cable spreading room, I/O cabinet, etc.
6) Energy sources of devices, such as electrical power, air supply, and hydraulic fluid supply. Identify voltage, pressure, and other applicable requirements. For electrical sources, identify circuit or disconnect numbers.
7) Process lines and equipment sufficient to describe the process side of the loop and provide clarity of control action. Include what is being measured and what is being controlled.
8) Actions or fail-safe positions (electronic, pneumatic, or both) of control devices such as controllers, switches, control valves, solenoid valves, and transmitters (if reverse-acting).
Additional information needs to be considered for its effectiveness in accommodating the intended uses.
Stated below are typical examples of items for inclusion at the user’s discretion.
1) Process equipment, lines, and their identification numbers, source, designation, or flow direction.
2) Reference to supplementary records and drawings, such as installation details, P&IDs, location drawings, wiring diagrams or drawings, and instrument specifications.
3) Specific location of each device, such as elevation, area, panel subdivision, rack or cabinet number and location, I/O location, etc.
4) Cross reference between loops that share a common discrete component, such as multi-pen recorders, dual indicators, etc.
5) References to equipment descriptions, manufacturers, model numbers, hardware types, specifications or data sheets, purchase order numbers, etc.
7) Software reference numbers, such as I/O addresses, control block types and names, network interfaces, point names, etc.
8) Engraving or legend information that helps identify the instrument or accessory.
- Loop Diagram Question
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- Engineering Logic Diagrams
- Electrical Schematics
- Junction Box Schedule