Logic Representation

Functional Logics

• Systems designed to provide the safe start up, shut down and operation of units. • They use a system of locks and interlocks that prevent unsafe situations developing. • A logic system consists of inputs and outputs, interconnected by gates and timers. • The system is designed to only allow

Starter Motor

Neutral

Output

Switc Input

Logic System

Input

Input

Switc

Switc

Functional Logic • Look like a series of boxes connected to other boxes via signal lines • The lines connect inputs to gates, timers etc to the final element box. • The signals are based on the Binary system • Signals are either 1 or 0 • Healthy Signal = 1 • Unhealthy Signal = 0

•

Any signal failure for example due to a power failure would cause a • If a final element is a solenoid, the solenoid will be energised in normal operation to • keep Whenthe thesystem solenoid is de-energised alive. the system will trip, to provide its 31-XE105 FUEL GAS

• Logics sheets have coded circles and symbols connected off them. • Logic sheets are read from left to right.

A functional logic diagram may encompass, several sheets of functional logic. Each of these sheets is necessary to show the interrelationship of a safeguarding logic system The sheets must be integrated with each other. Each sheet has an identifying number in the bottom right hand corner.

Functional Logics

Logic Sheet Number

SAFEGAURDING DEB.FEEDGAS

-

FRACTIONATOR SAUDIARAMCO SHELL REFINERT COMP.

Logic Sheet Identification Number

P

Signals that leave, enter, or transfer on a sheet are displayed by a circle with the sheet number entered in the circle.

The identifying number in a circle on the logic diagram gives the identity of the functional logic sheet where the signal originates from, or the

A functional logic sheet may have several inputs/outputs to other sheets. Sheet 13

Sheet 11

A 14

Sheet 14

A 13

C 12

Sheet 12

C 11

D 14

Sheet 14

D 11

Fail Safe Concept

Healthy 1 Unhealthy 0

Top Section is defined as healthy and generates a logical 1 31-PEA-07


If signal is less than high high setting then output is healthy and gives a 1

Fuel Gas IfBurner signal is more than high high

setting then output is unhealthy and gives a 0

Bottom Section is defined as unhealthy

1 0

High High setting = 3.5 bar

3.3 3.0 bar

31-PEA-07


Fuel Gas Burner

System Healthy

1

High High setting = 3.5 bar

3.6 bar

31-PEA-07

Fuel Gas to Burner


0

System Unhealthy

Unhealthy

OF F

0

0

1

1 Healthy

ON

Two Position Rotary Switch Position1

31-HE15 Emergency Shutdown Signal is 1 when not actuated

1

Two Position Rotary Switch Position 2

31-HE15 Emergency Shutdown Signal is 0 when actuated

0 Signal out known as the “Y” output

Signal to Input box Output greater than Low Low Condition Healthy Level Leg 31-LEA-20 Range 4 to 20ma Trip value 63% = 14.08 ma output

Input Box Tuned to trip the contacts. In this case at 14.08m a

>LL

31-LEA-20

Tuned Relay 0 or 1 output Output 15ma

1

Signal to Input box Output lower than Low Low Condition Unhealthy Level Leg 31-LEA-20 Range 4 to 20ma Trip value 63% = 14.08 ma output

Input Box Tuned to trip the contacts. In this case at 14.08m a

>LL

31-LEA-20

Tuned Relay 0 or 1 output Output 14 ma

0

Signal to Input box Output lower than Low Low Condition Unhealthy Level Leg 31-LEA-20 Range 4 to 20ma Trip value 63% = 14.08 ma output

Input Box Tuned to trip the contacts. In this case at 14.08m a

>LL

31-LEA-20

Tuned Relay 0 or 1 output Output 14 ma

Relay Trips

0

Input Box

Gates and Timers Final Element Box

Gates Device that performs a simple logic function

X1 X2

>

Y

A Truth Table shows the Logic of the Gate X1 X2 Y

0 0 1 1 0 1 1 1

0 0 1 1

A Truth Table shows the Logic of the Gate X1 X2 Y X1 1 X2 0

1

>

Y

0 0 1 1 0 1 1 1

0 0 1 1

If X1 is 1 X2 is 0 Y is 1

Truth Table

X1 X2 Y

X1 X2

> “OR” GATE

Y

0 10 01 1 1

0 0 1 1

Needs X1 or X2 to be 1 for Y to be 1

Truth Table

X1

1

X2

0

X1 X2 Y

>

1 Y

“OR” GATE

0 10 01 1 1

0 0 1 1

Needs X1 or X2 to be 1 for Y to be 1

Truth Table

X1

1

X2

0

X1 X2 Y

>

1 Y

“OR” GATE

0 10 01 1 1

0 0 1 1

Needs X1 or X2 to be 1 for Y to be 1

Truth Table

X1

0

X2

1

X1 X2 Y

>

1 Y

“OR” GATE

0 10 01 1 1

0 0 1 1

Needs X1 or X2 to be 1 for Y to be 1

Truth Table

X1

0

X2

0

X1 X2 Y

>

0 Y

“OR” GATE

0 10 01 1 1

0 0 1 1

Needs X1 or X2 to be 1 for Y to be 1

Truth Table

X1

1

X2

1

X1 X2 Y

+

0 Y

0 10 01 1 0

0 0 1 1

“EOR” GATE (Exclusive OR gate)

When X1 and X2 are both 1 signal = 0

Truth Table

X1

1

X2

1

X1 X2 Y

+

0 Y

0 10 01 1 0

0 0 1 1

“EOR” GATE (Exclusive OR gate)

When X1 and X2 are both 1 signal = 0

Truth Table

X1 X2 Y

X1 X2

&

Y

“AND” GATE

0 10 0 10 1

0 0 1 1

Needs X1 and X2 to be 1 for Y to be 1

Truth Table

X1

1

X2

0

X1 X2 Y

&

0 Y

“AND” GATE

0 10 0 10 1

0 0 1 1

Truth Table

X1

0

X2

1

X1 X2 Y

&

0 Y

“AND” GATE

0 10 0 10 1

0 0 1 1

Truth Table

X1

1

X2

1

X1 X2 Y

&

1 Y

“AND” GATE

0 10 0 10 1

0 0 1 1

Truth Table

X

Y

“Invert Gate” GATE When X = 0 Y = 1

X Y

0 1 1 0

(or NOT Gate)

Truth Table

X

0

1 Y

“Invert Gate” GATE

X Y

0 1 1 0

(or NOT Gate)

Truth Table

X

1

0 Y

“Invert Gate” GATE

X Y

0 1 1 0

(or NOT Gate)

Timers •Delay the acceptance of a healthy signal •Extend recognition of a healthy signal •Hold a healthy or unhealthy signal for a period of time

Delay Timer

X

t= 5sec

1 signal starts timer 1 X 0

t

5sec 1 Y 0

Y

1

0 TIME Output only after 5 seconds delay

5 Second Delay Timer OFF Stop

Start

5 Second Delay Timer OFF Stop

Start

5 Second Delay Timer

Stop

Start

Extension Timer

Y

X

t= 5sec

1 signal starts timer 1 X 0 1 Y 0

t 0

1

5sec

TIME Output Continues for 5 seconds

Double Acting Timer

X

t= 5sec

1 signal starts timer 1 X 0 1 Y 0

Y

t 0

Output only after 5 seconds delay

t

5sec

5sec

1 TIME Output Continues for 5 seconds

Pulse Timers

X

t=

1 X 0 1 Y 0

Y

t

t

TIME Output will pulse to either 1 or 0 for the time shown

Alarms and Indicators Signal=1 alarm is off Emergency Priority Alarm

Signal=1 alarm is off Locally Mounted panel Alarm

Signal=1 light is on Local Running Light

MOS

Maintenance Overide Switches 31-HI-907

POS 5

1

Maintenance Overide

Outputs 1 when switch in overide position Otherwise signal output = signal input

Used for Trip Testing

OOS Operational Overide Switches 30-HI-32 Operational Overide

OVERIDE

1

NORMA L

Outputs 1 when switch in overide position When in normal position signal output = signal input

Used for Start Ups

Final Element Boxes Receiving Boxes

K-3101

Logical 1 TRIP

DEB.FEED COMP.

Compressor is RUNNING when signal is 1

Final Element Boxes Receiving Boxes

K-3101

Logical 0

TRIP

DEB.FEED COMP.

Compressor is Tripped when signal is 0

Final Element Boxes Receiving Boxes

O

0

C

31-XE-105

FUEL GAS TO F-3101

Logical 0 Closes Fuel Gas Valve

No Flow of gas to furnace

Gas Flow

Final Element Boxes Receiving Boxes

Gas Flow

Logical 1 Opens Fuel Gas Valve

1

O C

31-XE-105

FUEL GAS TO F-3101

Valve opens and gas flows to Furnace

Final Element Boxes Receiving Boxes

0

C

51-XE-113

O

Nitrogen Purge

Logical 0 Opens Nitrogen Valve

Nitrogen Flow

Final Element Boxes Receiving Boxes

Gas Flow

Logical 1 Opens Fuel Gas Valve

1

O C

31-XE-105

FUEL GAS TO F-3101

Valve opens and gas flows to Furnace

Final Element Boxes Receiving Boxes

0

C

51-XE-113

O

Nitrogen Purge

Logical 0 Opens Nitrogen Valve

Nitrogen Flow

Final Element Boxes Receiving Boxes

Logical 1 Closes Nitrogen Valve

1

C

51-XE-113

O

Nitrogen Purge

Nitrogen Flow

Final Element Boxes Receiving Boxes

Nitrogen Flow

Logical 1 Closes Nitrogen Valve

1

C

51-XE-113

O

Nitrogen Purge

Valve closes and Nitrogen flow stops

Summary

Functional logics are used to quickly and safely shutdown equipment where a failure would Logics are also used to ensure plant is started safely using the correct procedure, e.g. start up of the sulphur A knowledge of functional logic sheets provides a useful tool to better understanding of the safeguarding Try working through the logic sheets for your block with a colleague, this will help to reinforce your

The End

Device that performs a simple logic function

X1 X2

> “OR” GATE

Y

O C

51-XE-119

•Functional logic sheets look like a series of boxes connected to other boxes via signal lines. •The lines connect inputs, to gates, timers etc, to the Final Element Box. •The logical arithmetic is based on the binary system. This requires that the signals used be either “1”or "O".

Healthy 1 Unhealthy

Health y 1

0kg Health y

1kg Unhealth y

Identifying numbers and letters Input boxes. Circuits. (trip cards identifies numbers and letters.) Alarm signals Overrid es Gates,(a.) "AND",(b.) “OR”, (c.) "INVERT" Timers, "Delay", "Extension", "Pulse" Final Element boxes.