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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