By the end of this lecture, student should be able to: ◦ Explain electro-hydraulic components symbol and

function: series and parallel circuits, open/close contact switch, OR/AND logic circuit, relay, coil and solenoid

◦ Design and analyze memory circuit

1. Open Contact Switch

2. Closed Contact Switch

3. Changeover Contact Switch – a combination of an Open and a Closed Contact Switch. Usually used on Relay and Limit Switch.

YES (Identity) Gate

+24V

0V

NOT (Negation) Gate +24V

0V

OR (Conjunction) Gate +24V

0V

AND (Disjunction) Gate +24V

0V

+24V

0V

Coil

Solenoid

IMPORTANT COMPONENTS IN ELECTRO-HYDRAULIC SYSTEMS

RELAY

SOLENOID

Consists of a coil and a set of changeover contact switch

Its function includes:

1. To help switch over small current to larger current

2. To help switch over small voltage to larger voltage

3. Consists of multiple large contact switches for simultaneous switching of multiple outputs

4. Safety feature: Interlock capability

Coil

Coil connections

Contacts

Contact connections

Return spring

Cover

Symbol

A1

A2 11

12 14

21

22 24

Armature

Symbol

A1

A2 11

12 14

21

22 24

A1 A2 4 2 1

Symbol

A1

A2 11

12 14

21

22 24

A1 A2 4 2 1

Symbol

A1

A2 11

12 14

21

22 24

A1 A2 4 2 1

Symbol

A1

A2 11

12 14

21

22 24

A1 A2 4 2 1

The circuit on the right is a direct connection without using relay. The lamp will switch on as soon as the contact switch is closed.

However, if there is a power surge from the main, then the user will experience some form of electric shock.

+24V

0V

The circuit on the right is an indirect connection with a relay (K1). Once the switch is pressed, relay coil (K1) will be energized. The coil will then closes the relay switch thus, switching the lamp.

The safety measure here is that, if there is a power surge from the 240V, then the user will be protected from any form of electric shock.

+24V

0V

K1

K1

2 4 0 V

2 different circuits

A solenoid is like a coil of the relay

When it is energized, it will switch on the valve, similar to turning on the hand lever of a normal valve.

If it is a single solenoid valve, then the valve will switch off automatically through a spring mounted at the opposite end of the valve.

If it is a double solenoid valve, then the valve will switch off only after the second solenoid is being energized.

Single Solenoid Valve Double Solenoid Valve

Hydraulic Circuit Symbol Electrical Circuit Symbol

A B

P T

Y1 Y2

A B

P T

Y1Y1

Y1 Y2

F=0

A B

P T

Y1 Y2

+24V

0V

S1

K1

K1

Y1

S2

K2

K2

Y2

Relevancy:

1. Used to build Continuous Cycle circuit.

2. Used to latch a circuit for continuous supply of electricity to a particular line.

3. Used when replacing a double solenoid valve to a single solenoid valve of a circuit, without changing the originality of the circuit function.

Memory ON (Dominant Set)

+24V

0V

ON

K1

K1

OFF

K1

• When ON is pressed, Relay coil K1 will be energized. Both relay K1 switches will close. This means, while the lamp turns on, the relay switch will continuously energize the coil. Therefore, the lamp is permanently on. Only when the OFF button is pressed, the lamp will switch off.

• To confirm that this is a Memory ON circuit, press both ON and OFF together. The lamp will still light ON.

Memory OFF (Dominant Reset)

• The function of this circuit is similar to the previous Memory ON circuit. However, please note that the OFF button is placed below the ON button, not parallel!

• To confirm that this is a Memory OFF circuit, press both ON and OFF together. The lamp will NOT light ON.

+24V

0V

ON

K1

K1

OFF

K1

Proximity -> closeness

Detect close objects without contact.

Various types:

1. Inductive sensor

2. Capacitive sensor

3. Optical sensor

Used to sense only metal type of object.

Used to sense only high density objects.

Used to sense only reflective type of object.