electro-pneumatics m3 teacher version

Electro-Pneumatics

Module 3: Logic Operations in Electro-Pneumatics

PREPARED BY

Academic Services

August 2012

Applied Technology High Schools, 2012

ATM-414 Electro-Pneumatics

2 Module 3: Logic Operations in Electro-pneumatics

Module 3: Logic Operations in Electro-

pneumatics Module Objectives

After the completion of this module, the student will be able to:

1- Explain the concept of logic operation (OR circuits).

2- Explain the concept of logic operation (AND circuits).

3- Describe, Explain and construct a simple AND/OR circuits.

4- Describe and use the latching circuits.

Module Contents

1 Logic operations-OR circuit 3

2 Truth table of the OR circuit 4

3 Logic operations-AND circuit 5

4 Truth table of the AND circuit 6

5 Practical Task 1 7


7 Latching Circuits 15

8 Types of latching 16


10 References 22


Module 3: Logic Operations in Electro-pneumatics 3

Logic Operations

In order to produce the required

movements by pneumatic cylinders under

certain conditions, it is often necessary to

combine signals from several control

elements through some logic operations

such as:

1. OR circuits

2. AND circuits.

1- Logic operation - OR circuit

The OR circuit has two inputs and a single

output. The aim is to be able to extend

the piston rod of a cylinder with two

different input elements, pushbutton S1

and S2. The contacts of the pushbuttons

S1 and S2 are arranged in parallel

branches in the circuit diagram as shown

in Fig. 3.1.b.

As long as no pushbutton is pressed, the solenoid valve remains in the

normal position. The piston rod is

retracted.

If at least one of the two pushbuttons is pressed, the solenoid valve switches

to the actuated position. The piston rod

advances.

When both switches are released. The solenoid valve switches to the normal

position. The piston rod is retracted.

(a)

(b)

Fig. 3.1:

(a): Pneumatic circuit

(b): Parallel connection of two contacts (OR circuit)

+24V

0V

S1

3

4

Y1

S2

3

4

1 2 3

4 2

51

3Y1



Truth table of the OR circuit:

The truth table depicts the status of the output in relation with specific

inputs. Let us assume the following

0: push buttons are not pressed and thus there is no input signal. 1: push button pressed and thus the input signal exists. Y1 is 0 means the solenoid valve is not activated Y1 is 1 means the solenoid valve is activated

The table below shows the possible outputs based on the input operating

conditions.

S1 S2 Y1

0 0 0

1 0 1

0 1 1

1 1 1

Fig. 3.2: Truth table of the OR circuit.



2- Logic operation - AND circuit

The AND circuit has two inputs and a

single output. The output of the AND

circuit exists only when both inputs are

existing. In this case the piston rod of a

cylinder will be advanced only if both

pushbuttons S1 and S2 are pressed at the

same time. The Two pushbutton switches

are arranged in series in the circuit

diagram as shown in Fig.3.3.b

As long as neither or only one of the two pushbuttons is pressed, the

solenoid valve remains in the normal

position and the piston rod is retracted.

If both pushbuttons are pressed at the same time, the solenoid valve switches

to the actuated position and the piston

rod advances.

When at least one of the switches is released, the solenoid valve switches

to the normal position and the piston

rod retracted.

(a)

(b)

Fig. 3.3:

(a): Pneumatic circuit

(b): Series connection of two contacts (AND circuit)

+24V

0V

S1

3

4

Y1

S2

3

4

1

4 2

5 1 3Y1



Truth table of the AND circuit:

The truth table depicts the status of the output in relation with specific

inputs. Let us assume the following

0: push buttons are not pressed and thus there is no input signal. 1: push button pressed and thus the input signal exists. Y1 is 0 means the solenoid valve is not activated Y1 is 1 means the solenoid valve is activated

The table below shows the possible outputs based on the input operating

conditions.

S1 S2 Y1

0 0 0

1 0 0

0 1 0

1 1 1

Fig. 3.2: Truth table of the AND circuit.

Practical Task 1

Title: Operating a pneumatic press directly

Objectives:

Upon the completion of this task, the student should

1- Explain and use the AND connection practically to ensure a safe

operation.

2- Explain and use the OR connection practically.

3- Explain the direct (without using relays) control circuit with AND/OR.

4- Be able to use the FluidSIM software as well as workstations.



Problem description:

The pneumatic press that is shown in the Fig.3.3 has to be operated by

two switches at the same time in order to protect the operator hands

from any possible injury during the press operation. The press will be

released automatically by a limit switch. However, another switch has to

be provided to release the press in case of the limit switch malfunction.

Fig.3.3



Required components:

1- Double acting cylinder

2- 5/2 Directional control valve, double solenoid

3- Power supply

4- Switch blocks

Required procedures:

1. Draw the elector-pneumatic circuit using the FluidSim software

2. The speed of the forward and backward stroke of the cylinder rod is

adjustable

3. Test the circuit functions against any errors or mistakes.

4. Construct the circuit on the workstation

5. Write down your notes and observations.

Pneumatic circuit Electric circuit



Observations and notes ............................................................................................................

............................................................................................................

............................................................................................................

............................................................................................................

............................................................................................................

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............................................................................................................

............................................................................................................

Practical Task 2

Title: Operating a pneumatic press indirectly

Objectives:

Upon the completion of this task, the student should

1- Explain and use the AND connection practically to ensure a safe

operation.

2- Explain and use the OR connection practically.

3- Explain the indirect (using electric relays) control circuit with AND/OR.

4- Be able to use the FluidSIM software as well as workstations.


The problem description for this task is the same as for the above task

(task 1)



2- 5/2 Directional control valve, double solenoid

3- Power supply

4- Switch blocks

5- Relay blocks




1- Draw the elector-pneumatic circuit using the FluidSim software

2- Test the circuit functions against any errors or mistakes.

3- Construct the circuit on the workstation

4- Write down your notes and observations.


Observations ............................................................................................................

............................................................................................................

............................................................................................................

............................................................................................................



Class work (1)

1. Give an application example of where an AND circuit is used.

..

2. Give an application example of where an OR circuit is used.

3. The circuit below illustrates an electro-pneumatic system, answer the

following questions :

a) Explain how to extend and retract the cylinder.



b) For the electro- pneumatic system above, write the truth table.

S1 S2 S3 Y1

c) Convert the above electric circuit to control the pneumatic circuit

directly.



Home Work (1)

1. The circuit below illustrates an electro-pneumatic system. Answer the

following questions:

a) Is the above electric circuit direct or indirect control? Explain why.

b) What is the name of the part which is labeled as Y1?

..

c) What is the difference between K1 in branch 2 and K1 in branch 4?

d) What is the difference between K1 in branch 2 and Y1 in branch 4?



e) How to extend the piston of the above cylinder?

2. The truth table below represents a logic circuit controlling a single

solenoid 5/2 DCV, based on the table below draw the electric and the

pneumatic circuit.

S1 S2 S3 Y1

0 0 0 0

1 0 0 0

0 1 0 0

0 0 1 0

1 1 0 0

1 0 1 1

0 1 1 1

1 1 1 1

.



Latching Circuits

Definition of latching: It is a process where the relay contacts remain on

without keeping the relay coil energized. In other words, it is required

sometimes to keep the circuit powered for a certain function even though

a pushbutton switch is released to the open position. Fig. 3.4 illustrates

the concept of latching before activating the switch S1 and Fig.3.5 after

activating switch S1.

Fig.3.4 Before latching

Fig.3.5 After latching



Way of operation:

When the ON pushbutton switch is

actuated as shown in Fig.3.5.a, the relay

coil is energized and thus the contact K1

closes. Even after the ON pushbutton

switch is released the electric current

continues to flow via contact K1 through

the coil, and the relay remains in the

actuated position. The on signal is

stored. When the OFF pushbutton is

pressed the current flow is interrupted

and the relay becomes de-energized.

Types of latching:

1- dominant ON:

In Fig.3.5.a, if the ON and OFF

pushbuttons are both pressed at the

same time, the relay coil is energized.

Thats why the circuit in Fig.3.5.a is

called a dominant ON latching circuit.

1- dominant OFF:

In Fig.3.5.b, If both pushbuttons are

pressed simultaneously: the relay coil is

not energized. Thats why the circuit in

Fig.3.5.b is called a dominant OFF

latching circuit.

(a)

(b)

Fig. 3.5: Relay circuit with

latching

(a): Dominant ON

(b): Dominant OFF



Practical task 3

Title: Latching circuit

Objectives:

Upon the competition of this task, the student should be able to control

an electro-pneumatic system by using an electrical latching circuit.


Parts are to be pushed away from a multi-track gravity feed magazine

into a clamping device as shown below in Fig.3.6. By pressing a

pushbutton switch the parts are pushed out of the multi-track gravity feed

magazine by a slide. After the slide has reached the forward end position

it has to return to its start position.

Hint: A relay with latching function is to be used for signal storage.

Fig3.6



2- 5/2 DCV, single solenoid

3- Power supply

4- Switches block

5- Relay block

6- Limit switch




1- Draw the electro-pneumatic circuit using the FluidSim software

2- Test the circuit functions against any errors or mistakes.

3- Construct the circuit on the workstation

4- Write down your notes and observations.


Observations and notes ............................................................................................................

............................................................................................................

............................................................................................................

............................................................................................................

............................................................................................................

............................................................................................................



Class work (2)

1. Explain briefly the meaning of latching in electrical circuits

..

2. The circuit below illustrates an electro-pneumatic system. Answer the

following questions.

a) Which one is the latching circuit? Indicate the circuit number.

b) What type of switch are switches S1 and S2?

c) What is the meaning of the symbol shown under circuit 1?

+24V

0V

S113

14

K1A1

A2

K13

4

S21

2

Y1

K13

4

1 2 3

23

4 2

51

3Y1



d) What is the function of switch S2?

e) How to extend and retract the cylinder piston?

f) State whether the above electro-pneumatic system is controlled

directly or indirectly. Justify your answer



Home Work (2)

The circuit below illustrates an electro-pneumatic system. Answer the

following questions:

a) Is the electric circuit above directly or indirectly controlled? Why?

b) Which switch is used to operate the circuit?

..

c) Which branch represents the latching circuit?

..



d) Which switch is used to release (unlatch) the circuit?

e) Explain, how to extend the piston of the above cylinder?

f) Explain, how to retract the above cylinder?

References

1. Electro-pneumatic text book TP 201 2005 Festo

2. Electro-pneumatic work book TP201 2005 Festo

3. Electro-pneumatic work book TP202 advanced level Festo

electro-pneumatics m3 teacher version

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