Lecture 4 - Diagrams and variables (1)

Esta é uma pré-visualização de arquivo. Entre para ver o arquivo original

CP405 – Process Control
Lecture 4 – Diagrams and variables
Process flow diagram (PFD)
Shows major process units
Shows major process pipelines
May show some control
Doesn’t show instruments
Doesn’t show detail of pipelines and valves
Process flow diagram (PFD)
Piping and Instrumentation Diagram (P&ID)
PFD + 
Shows ALL pipework and valves
Shows instruments and controllers
Specifies pipe sizes
Specifies types of communications
Doesn’t specify plant arrangement
Piping and Instrumentation Diagram (P&ID)
Use for process design; process control design; safety (HAZOP); procedure writing; plant engineering; etc
Some ‘standards’ (e.g. ISA S5.1)but P&ID symbols tend to be very company specific
Piping and Instrumentation Diagram (P&ID)
P&ID Instrumentation
FY
023
Device ‘bubble’
Communication lines
Tag name
Tag identifier
Tag number
P&ID – tag identifiers
Letter
In 1stposition
Modifier (if used)
Followingletters
A
Analyser
Alarm
C
Anything
Controller
F
Flow rate
Ratio or fraction
I
Current
Indicator
L
Level
Light or Low
P
Pressure
R
Radiation
Recorder or printer
T
Temperature
Transmitter
P&ID – tag names
FI005 – flow indicator
TC123 – temperature controller
PIR059 – pressure indicator/recorder
LIC567 – level indicator/controller
Numbering convention depends on company
Some number all the components of a loop with the same number
Some number similar instruments in sequence
P&ID – tag numbers
P&ID – Bubble shapes
Thanks to the University of Rochester for this diagram
Field mounted distinct instruments
Shared displays
SCADA vs PLCs
P&ID – Communication lines
Thanks to the University of Rochester for this diagram
P&ID – Example
Process control systems are information processing systems
The take information from process, decide what to do about it, and then send information back to the process on what changes should be made
Processes, and their inputs and outputs, are quite different from what we talk about in process engineering
Control system variables and definitions
A process input is information that enters a process and, potentially, changes its state
There are two types of process inputs: disturbances and manipulations
Disturbances are process inputs that can change outside of the influence of the local control system
Manipulations are process inputs that are directly influenced by the local control system – they are control system outputs (the output of the control system is connected to a manipulated input)
Process inputs
A process output always comes from an instrument
All instrument outputs are process outputs
Process outputs are classed as either controlled variables or auxiliary variables
Controlled outputs are the target for active control
Auxiliary variables give more information about the process, but aren’t held at particular values
Process outputs
In control engineering, a process is something that converts input information into output information
Processes can be Single-input/Single-output(SISO), Multi-input/Single-output(MISO) or Multi-input/Multi-output(MIMO)
Standard control system analysis breaks MIMO and MISO systems into a number of SISO sub-processes
Processes from a control viewpoint
P&ID – Variables and Processes
Any questions?