Wednesday, February 25, 2015

How to design a P&ID? Part-3

Earlier two parts of designing a P&ID were from process perspective of a P&ID. Now in this present part we will deal with the instrument aspects of a P&ID. Some of the most common instruments which we are using in process industry are transmitters, gauges, indicators, control valves, on off valves etc. The parameters which we are interested may be flow, temperature, pressure, concentration etc. Before going to discuss further about instrumentation part in P&ID it is better to get familiarized with the instrumentation terms. Let’s get started


Letter
First letter
Succeeding letters
Measured or Initiating Variable
Modifier
Read out or passive function
Output function
Modifier
A
Analyzer

Alarm


B
Burner

Users Choice
Users Choice
Users Choice
C
Users Choice
Control

Control
Close
D
Users Choice
Differential



E
Voltage

Primary element


F
Flow
Ratio



G
Users Choice

Glass


H
Hand



High
I
Current

Indicate


J
Power
Scan



K
Time


Control Station

L
Level

Light

Low
M
Users Choice
Momentary


Medium
N
Users Choice

Users Choice
Users Choice
Users Choice
O
Users Choice

Orifice

Open
P
Pressure

Point test Connection


Q
Quantity
Integrate/Totalize



R
Radiation
Relief
Record


S
Speed
Safety

Switch

T
Temperature


Transmit

U
Multi variable

Multi function
Multi function
Multi function
V
Vibration


Valve, Damper

W
Weight, Force

Well


X
Unclassified
X-Axis
Unclassified
Unclassified
Unclassified
Y
State, Event
Y-Axis

Relay, Compute

Z
Position
Z-Axis

Driver, Actuator, unclassified final control element





Instrument tag identification

Instruments like equipment carry tag numbers. These tag numbers are very helpful in tracking the process parameters across the pipelines and equipment. Without the tag numbers confusion arises as lot of similar instruments exist in a process plant. Therefore tag philosophy of instruments is important. For example
LT – 3204
LT stands for Level transmitter (Prefix: Level, Suffix: Transmitter), 32 stands for reactor section and 04 stands for instrument number. Some of the most common instrument tags using in process industry are
  • PS : Pressure Switch
  • LIA : Level indicator alarm,
  • FIQC : Flow indicator totalizer and controller

Instrument symbols

Like valves and fittings we have symbols for instruments also. Each of them have a specific meaning and the reader should not confuse with the representation.


For example


Instrument abbreviations


AI                           
Analog Input
AO
Analog Output
BCD
Binary coded decimal
C
Computer
CPT
Control power transformer
DI
Digital input
DL
Data Logger
DO
Digital Output
FB
Feedback
FC
Fail closed
FI
Fail Intermediate
FO
Fail Open
FLP
Fail last position
FP
Fill port
FWD
Forward
KT
K – Type thermocouple
LC
Locked Closed
LO
Locked Open
MN       
Modbus network
MS
Motor starter
NC
Normally Closed
NO
Normally Open
PLC        
Programmable Logic Controller
PV
Process Variable
RSP
Remote set point
REV
Reverse
SP
Set point
EL
Elevation
IAR
Instrument Air

Transducer functions


A transducer is one which converts one form of signal to another. In P&ID it is necessary in some places where you need to mention the transducer function. Some of the most common transducer functions are as follows
  • Current to pneumatic convertor     :               I/P convertor
  • Pneumatic to current convertor      :               P/I convertor
  • Voltage to current convertor          :               E/I convertor
  • Voltage to pneumatic convertor     :               E/P convertor
  • Voltage to voltage convertor          :               E/E convertor











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