Overview of Loop Diagrams in Process Control Systems
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Loop
Diagrams
Chapter 07
–
Loop Diagrams
EMEC125
Overview
&
Definitions
•
Loop
diagrams are the
most popular of
all the documents generated
for
a
process control
system.
•
Definitions:
•
Loop Diagram
–
“A
schematic representation of
a
complete
hydraulic,
electric,
magnetic, or pneumatic
circuit.”
(International Society of Automation, 2003,
p.299)
•
Loop
–
“Instrumentation arranged
as a
combination of two
or
more
instruments or functions arranged so that
signals
pass from one to another
for
the purpose of measurement
and
indication or
control
of
a
process
variable. a) A
self-contained device that measures
and
controls
a
process
variable.” (International Society of Automation, 2009,
p.3.1.40)
Sample
Loop
Diagram
(CADtech
Consultants,
n.d.)
Loop_Diagram_Sample.pdf
1
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17
Loop
Diagrams
–
What’s
On
Them?
•
Everything
a
controls
technician needs
to
maintain
and/or install
a
system
of
instrumentation
•
Included
is:
•
Electrical and pneumatic
signal
connections
•
Power connections to instruments and
controls
•
Indication and
control
devices, along
with
the connections to the process, to
the
piping,
the ductwork,
vessels,
tanks,
etc.
•
Controllers whether computer or
pneumatic
•
Source
and service utilities
i.e.
compressed
air, water,
electrical
power,
etc.
•
Termination
information that includes the identification of junction box(es),
terminal strip numbers, terminal block numbers and possibly
even
pneumatic
port
numbers
Guidelines
•
ISA-5.4-1991 Instrument Loop
Diagrams
spell
out
a
few guidelines for
creating
loop
diagrams.
The standard
states:
•
Drawings
should
be
American
Society of Mechanical Engineers (ASME)
B
size
(11”
x
17”)
drawings.
•
Only one loop
should
be depicted on
a
loop
diagram.
•
Paper can be portrait or
landscape.
Landscape
is
the
preferred
and is
the most
common
orientation.
•
Should be divided into sections that relate to component locations, such
as
and according to
ISA-5.4:
•
Field or Field
Process
Area
•
Cable Spreading
Room
•
Computer I/O
Cabinet/Cabinet
•
Panel
Front
•
Control
Panel
•
Console
Developing
a Loop
Diagram
•
Development
can
start
when:
•
A
standard
has been established
as
to the
content.
•
The P&IDs are completed and
issued.
•
Specification forms have been completed.
•
All
devices and instruments have been specified and preferably
ordered.
•
Junction boxes,
if
used, have been
defined, a.k.a.
marshalling
panel.
•
Termination
diagrams
for control
computers are ready
for
loading.
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17
5
6
XXXX
1
2
3
Identify
junction
box
or
t
e
r
m
i
n
a
l
a
ss
e
m
b
l
y
4
Identify
each
c
o
nn
e
c
t
i
o
n
u
s
e
d
Instrument
terminals
or
ports
with
identifying letters,
numbers
or both.
(It
is
suggested
that
identifying
numbers
or letters
bethe
manufacturer’s
designations)
Instrument
Connections
“Symbols referenced
in ISA-5.1
and ISA-5.4 apply
for
instrument loop diagrams.
However,
expansion of those symbols to include connection points, energy sources
(electrical,
air,
hydraulic),
and instrument action
is
necessary to provide the
information required on instrument loop diagrams.” (The Instrumentation, Systems,
and Automation
Society,
1991,
p.12)
General terminal or bulkhead
symbol
Instrument terminals or
ports
Loop Diagram
–
Energy
Supply
TR
105
L1
L2
G
TT
S
104
S
WT
103
ES 115V,
60Hz
Panel
A,
Circuit
12
AS 20
PSIG
(IA or PA are optional
alternatives
for
air
supply)
HS 50
PSIG
Electrical Power
Supply
Identify electrical power supply
followed
by the
appropriate
supply
level
identification
and
circuit
number
or
disconnect
identification
Air
Supp
ly
Identify
air
supply
followed
by
air
supply
pre
ss
ur
e
Hydraulic fluid
Supply
Identify
hydraulic
fluid
followed
by
the
fluid
supply
pressure
Instrument
Action
•
Identifies the
response of
the device
to
applied signals. The signals
can be electronic
or
pneumatic.
•
A
transmitter and/or controller
can
provide
two actions, direct
or
reverse:
•
Direct Acting
–
The output
signal
increases
as
the process variable (PV)
increases.
•
Reverse Acting
–
The output
signal
decreases
as
the process variable (PV)
increases.
•
Loop diagram
instruments
should reference
the action as direct
or
reverse.
DIR can be used
for
direct and REV can be used
for
reverse.
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17
Instrument
Action
Instruments
TC
104
REV
LT
104
L
S
H
104
D
I
R
R
EV
These instrument
symbols show
the
control
action by placing an
acronym
for
the action near the instrument bubble. DIR
identifies the instrument as Direct Acting and REV identifies the
instrument as
Reverse
Acting. Because
most transmitters
are
direct acting the DIR designation is
optional
and if
not
present
the instrument can be assumed as direct
acting.
P&ID
Loop
100
1
0"
6
"
1
0"
10" 150
CS
004
1
"
P
I
C
100
P
IT
100
PV
100
6
7
6"
300
3-1
5
P
S
I
G
PIT-100-(B)
I
S
O
PIT
S
100
O
0-1
0
P
S
IG
E
L
EV
119'0
"
3-1
5
P
S
I
G
P
V-
100-(B)
A
S
10
0
P
S
I
G
1
0"
15
0
C
S
004
FO
I
PIC
O
AS
20
PSIG
S
100
REV
E
L
EV
11
4
'
6"
CONTROLLER:
M
O
DEL
N
O
:
S
P
E
C
:
NO:
E
L
EV
120'0
"
PV
100
VALVE:
M
O
DEL
N
O
:
S
P
E
C
:
NO:
Loop Diagram
P-100
Field
Process
Area
FROM
0
1-D
-001
TRANSMITTER:
M
O
DEL
N
O
:
S
P
E
C
:
NO:
3
A
S
2
0
P
S
IG
TO
F
L
A
R
E
NOTES:
1.
PV-100
FULLY
OPEN
AT
3
PSIG
FULLY
CLOSED
AT
15
PSIG
R
E
F
E
R
EN
C
E
D
R
A
WING
S
P&I
D
XX
X
I
N
S
T
A
L
L
A
TIO
N
DET
A
I
L
S
4
0
6
/0
6
/2
0
17
H
G
F
E
D
B
8
7
6
5
4
3
2
H
G
F
E
D
C
B
A
8
7
6
5
4
3
2
1
NCC
PLC
Training
Panel
Input
Temperature
Transducer/Transmitter
–
Loop
01
SIZE FSCM
NO
B
SCALE
None
DWG
NO
REV
A
NCC145-04
02
SHEET
1 OF
1
1
ZONE
REV
REVISIONS
DESCRIPTION
DATE APPROVED
C
F4 02 Changed transducer from
Air
Products
to
Automation
Direct Universal
Mar.
3,
2012
F7
01
M
od
ifi
ed
w
iri
ng
for
Type
‘
K
’
T/C
Feb. 24,
2003
TT
01
PLC
01
PLC
01
TT
01
TE
01
TE
01
5
Loop diagrams are essential documents in process control systems, providing schematic representations of hydraulic, electric, magnetic, or pneumatic circuits. They detail instrumentation arrangements, signal connections, power connections, and termination information. Guidelines and standards for creating loop diagrams are outlined, emphasizing the importance of accuracy and completeness in development. The diagrams include symbols for instrument connections, energy supplies, and instrument actions, ensuring clear communication for maintenance and installation purposes.
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Presentation Transcript
06/06/2017 LoopDiagrams Chapter 07 Loop Diagrams EMEC125 Overview &Definitions Loop diagrams are the most popular of all the documents generated for a process controlsystem. Definitions: Loop Diagram A schematic representation of a complete hydraulic, electric, magnetic, or pneumatic circuit. (International Society of Automation, 2003, p.299) Loop Instrumentation arranged as a combination of two or more instruments or functions arranged so that signals pass from one to another for the purpose of measurement and indication or control of a process variable. a) A self-contained device that measures and controls a process variable. (International Society of Automation, 2009, p.3.1.40) Sample LoopDiagram Loop_Diagram_Sample.pdf (CADtech Consultants, n.d.) 1
06/06/2017 Loop Diagrams What s On Them? Everything a controls technician needs to maintain and/or install a system of instrumentation Includedis: Electrical and pneumatic signalconnections Power connections to instruments andcontrols Indication and control devices, along with the connections to the process, to the piping, the ductwork, vessels, tanks,etc. Controllers whether computer or pneumatic Source and service utilities i.e. compressed air, water, electrical power, etc. Termination information that includes the identification of junction box(es), terminal strip numbers, terminal block numbers and possibly even pneumatic portnumbers Guidelines ISA-5.4-1991 Instrument Loop Diagrams spell out a few guidelines for creating loop diagrams. The standardstates: Drawings should be American Society of Mechanical Engineers (ASME) B size (11 x 17 )drawings. Only one loop should be depicted on a loop diagram. Paper can be portrait or landscape. Landscape is the preferred and is the most commonorientation. Should be divided into sections that relate to component locations, such as and according toISA-5.4: Field or Field ProcessArea Cable SpreadingRoom Computer I/OCabinet/Cabinet PanelFront ControlPanel Console Developing a LoopDiagram Development can startwhen: A standard has been established as to the content. The P&IDs are completed andissued. Specification forms have been completed. All devices and instruments have been specified and preferably ordered. Junction boxes, if used, have been defined, a.k.a. marshalling panel. Termination diagrams for control computers are ready for loading. 2
06/06/2017 Instrument Connections Symbols referenced in ISA-5.1 and ISA-5.4 apply for instrument loop diagrams. However, expansion of those symbols to include connection points, energy sources (electrical, air, hydraulic), and instrument action is necessary to provide the information required on instrument loop diagrams. (The Instrumentation, Systems, and Automation Society, 1991,p.12) Identify junction box or terminalassembly XXXX 1 2 3 4 Identify each Instrumentterminalsorports with identifying letters, numbers or both. (It is suggested that identifying numbers or lettersbethe manufacturer s designations) 7 8 15 16 FIC 103 1 2 5 6 connection used Instrument terminals orports General terminal or bulkheadsymbol Loop Diagram EnergySupply Electrical PowerSupply Identify electrical power supply followed by the appropriate supply levelidentification and circuit number ordisconnect identification L1 L2 G ES 115V,60Hz Panel A,Circuit12 TR 105 AS 20PSIG (IA or PA are optional alternatives forairsupply) AirSupply Identify airsupply followed by air supply pressure TT S 104 Hydraulic fluidSupply Identify hydraulic fluid followedby the fluid supply pressure WT S HS 50PSIG 103 InstrumentAction Identifies the response of the device to applied signals. The signals can be electronic orpneumatic. A transmitter and/or controller can provide two actions, direct or reverse: Direct Acting The output signal increases as the process variable (PV) increases. Reverse Acting The output signal decreases as the process variable (PV) increases. Loop diagram instruments should reference the action as direct or reverse. DIR can be used for direct and REV can be used for reverse. 3
06/06/2017 Instrument Action Instruments REV LT LSH 104 TC 104 104 REV DIR These instrument symbols show the control action by placing an acronym for the action near the instrument bubble. DIR identifies the instrument as Direct Acting and REV identifies the instrument as Reverse Acting. Because most transmitters are direct acting the DIR designation is optional and if not present the instrument can be assumed as directacting. P&ID Loop100 PIC 100 PIT 100 PV 100 1" 10" 150 CS004 10" 10" 6" 300 6 7 6" Loop Diagram P-100 Field ProcessArea FROM 01-D-001 TRANSMITTER: MODELNO: SPEC: NO: 3 AS 20 PSIG CONTROLLER: MODELNO: SPEC: NO: 0-10 PSIG PIT S 100 O I PIC O 3-15 PSIG PIT-100-(B) AS 20 PSIG S 100REV 10"150CS 004 ELEV 114'6" ELEV 119'0" 3-15 PSIG PV-100-(B) AS 100 PSIG I S O FO ELEV 120'0" PV 100 VALVE: MODELNO: SPEC: NO: TO FLARE REFERENCE DRAWINGS P&ID XXX INSTALLATION DETAILS NOTES: 1. PV-100 FULLYOPEN AT 3 PSIG FULLYCLOSEDAT 15PSIG 4
06/06/2017 8 7 6 5 4 3 2 1 PLC 01 H H PLC 01 TT 01 TT 01 G G F F TE 01 TE 01 E E D D REVISIONS DESCRIPTION ZONE REV DATE APPROVED C C F4 02 Changed transducer from Air Products to Automation Direct Universal Mar. 3, 2012 F7 01 Modified wiring for Type K T/C Feb. 24, 2003 B B NCC PLC Training Panel Input Temperature Transducer/Transmitter Loop 01 DWG NO REV A 02 A SIZE FSCMNO NCC145-04 B SHEET 1 OF 1 SCALE None 1 8 7 6 5 4 3 2 5
