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page 594

35. PROCESS MODELLING

• Instrumentation Symbols,

Table 2: ANSI/ISA-S5.1-1984 Instrumentation Symbols and Identification

LETTER

FIRST LETTER

SECOND LETTER

 

 

 

 

 

 

A

Analysis

Alarm

 

 

 

B

Burner, Combustion

User’s Choice

 

 

 

C

User’s Choice

Control

 

 

 

D

User’s Choice

 

 

 

 

E

Voltage

Sensor (Primary Element)

 

 

 

F

Flow Rate

 

 

 

 

G

User’s Choice

Glass (Sight Tube)

 

 

 

H

Hand (Manually Initiated)

 

 

 

 

I

Current (Electric)

Indicate

 

 

 

J

Power

 

 

 

 

K

Time or Time Schedule

Control Station

 

 

 

L

Level

Light (pilot)

 

 

 

M

User’s Choice

 

 

 

 

N

User’s Choice

User’s Choice

 

 

 

O

User’s Choice

Orifice, Restriction

 

 

 

P

Pressure, Vacuum

Point (Test Connection)

 

 

 

Q

Quantity

 

 

 

 

R

Radiation

Record or Print

 

 

 

S

Speed or Frequency

Switch

 

 

 

T

Temperature

Transmit

 

 

 

U

Multivariable

Multifunction

 

 

 

V

Vibration, Mechanical Analysis

Valve, Damper, Louver

 

 

 

W

Weight, Force

Well

 

 

 

page 595

Table 2: ANSI/ISA-S5.1-1984 Instrumentation Symbols and Identification

LETTER

FIRST LETTER

SECOND LETTER

 

 

 

 

 

 

X

Unclassified

Unclassified

 

 

 

Y

Event, State or Presence

Relay, Compute

 

 

 

Z

Position, Dimen sion

Driver, Actuator, Unclassified

 

 

 

• Line symbols include,

Capillary Tube

Electric Signal

EM, Sonic, Radioactive

Hydraulic

Pneumatic

Process

• Sensor and actuator symbols include,

FE 11

orrifice plate

EE 2

magnetic

FV

11

control valve

page 596

FE 11

venturi or nozzle

FI 6

rotameter

• An example of a process diagram is given below,

page 597

35.1 REFERENCES

Paques, Joseph-Jean, “Basic Safety Rules for Using Programmable Controllers”, ISA Transactions, Vol. 29, No. 2, 1990.

35.2 PRACTICE PROBLEMS

1.The best location for the PLC enclosure is:

a)close to the incoming power

b)in the control room

c)close to the machine or process

d)far away from the machine or process

(ans. c)

2. Typically, programmable controller systems installed inside an enclosure can withstand a maximum of:

page 598

a)60°C outside the enclosure

b)50°C outside the enclosure

c)60°C inside the enclosure

d)50°C inside the enclosure

(ans. c)

3.Input/Output racks are not typically placed:

a)adjacent to the CPU

b)beside the power supply

c)directly above the CPU

d)in a remote enclosure

(ans. c)

4.The I/O placement and wiring documents should be updated:

a)during maintenance

b)every time there is a change

c)at the end of the project

d)during the documentation

(ans. b)

5. What steps are required to replace a defective PLC?

(ans. in a rack the defective card is removed and replaced. If the card has wiring terminals these are removed first, and connected to the replacement card.)

6. Draw the electrical schematic and panel layout for the relay logic below. The system will be connected to 3 phase power. Be sure to include a master power disconnect.

A C

B

B

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