acetatos electrohidráulica

Electrohydraulics

Set of OverheadTransparencies

Basic Level

D.OT-TP601-GB

095051

Learning System for Automation and Communications

Order no.: 095051Designation: E.-HYDR. FOLIENDescription: D.OT-TP601-GBEdition: 2/96Graphics: T. Ocker, D. SchwarzenbergerLayout: 23.2.96, M. SchwarzAuthor: D. Scholz

© Copyright by Festo Didactic KG, D-73734 Esslingen, 1996

All rights reserved, including translation rights. No part of this publica-tion may be reproduced or transmitted in any form or by any means,electronic, mechanical, photocopying, or otherwise, without the priorwritten permission of Festo Didactic KG.

This set of overhead transparencies has been designed for use withthe basic level of the technology package TP600 “Electrohydraulics”.The set of overhead transparencies and the technology package formpart of Festo Didactic KG’s “Learning System for Automation and Com-munications”.

Introduction

The 30 transparencies in this set have been optimised from the didacticand methodological points of view. Each transparency is accompaniedby a short text which provides the trainer with a quick overview of thetraining contents of the transparency concerned.

Training contents:

• Basic principles of electrohydraulics

• Function and use of electrohydraulic components

• Basic principles of electrical engineering

• Production and interpretation of standard hydraulic and electricalcircuit diagrams

The text sheet includes a complete illustration of the transparency, incertain cases with additional explanations and legends which the trainercan enter on the transparency in the course of a training session.

The advantages of this concept are:

• The trainer can add to the transparencies step by step in the courseof a training session.

• The trainer is thus able to create a lively and interesting atmosphere.

• The provision of accompanying text means less preparation work forthe trainer.

601Festo Didactic

Festo Didactic601 Festo Didactic

Electrohydraulic press . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 1Contents

Schematic layout of an electrohydraulic installation . . Transparency 2

Electrical power supply unit . . . . . . . . . . . . . . . . . . . . . Transparency 3

Electrical circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 4

Measuring circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 5

Ohm’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 6

Rectifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 7

Analogue, digital and binary . . . . . . . . . . . . . . . . . . . . . Transparency 8

Momentary and sustained contact switches . . . . . . . . Transparency 9

N/O, N/C and changeover contacts . . . . . . . . . . . . . . Transparency 10

Limit switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 11

Proximity switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 12

Solenoid (electromagnet) . . . . . . . . . . . . . . . . . . . . . . . Transparency 13

Electrohydraulic converters (solenoid valves) . . . . . . . Transparency 14

Dry and wet solenoids . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 15

Solenoid valve connections . . . . . . . . . . . . . . . . . . . . . . Transparency 16

Relays and contactors . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 17

Direct and indirect activation . . . . . . . . . . . . . . . . . . . . Transparency 18

Signal inversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 19

Latching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 20

Circuit diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 21

Hydraulic power pack . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 22

Hydraulic circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 23

Electrical and hydraulic power . . . . . . . . . . . . . . . . . . . Transparency 24

Power losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 25

Pressure switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 26

4/3-way solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 27

4/3-way solenoid valve, piloted . . . . . . . . . . . . . . . . . . Transparency 28

Electrical safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 29

Hydraulic safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 30

Electrohydraulic pressTitle

• Function units: Motor with hydraulic pump, control panel, valvemanifold, cylinder.

Notes

• The hydraulic press is controlled via the electrical control panel.

• Electrical signals are used to activate the valves in the hydraulicinstallation.

• The electrohydraulic press is used to form rectangular troughs.

601-01-GB

Motor withhydraulic pump Valve manifold

Actuator(cylinder)

Control panel

1 Electrohydraulics Festo Didactic

Schematic layout of an electrohydraulic installationTitle

• Division of installation into signal control section and hydraulicpower section.

Notes

• Signal control section: Input and processing of electrical signals.

• Solenoid valves form the interface between the electrical signalcontrol section and the hydraulic power section.

• Hydraulic power section: Controls the flow of hydraulic fluid bymeans of solenoid valves. Actuators convert hydraulic energy intomotions.

601-02-GB

Signal control section

Signalinput

Powersupply

Hydrauliccylinder

Solenoidvalve

Hydraulicpowersupply

(conversion)

Signalprocessing

Power section

2 Electrohydraulics Festo Didactic

Electrical power supply unitTitle

• Connection to mains supply.Notes

• Supplies signal control section with specified or maximum voltageand current values.

• Functions in power supply unit: Voltage transformation, rectification,smoothing, stabilisation, fuse protection.

• In mobile hydraulic systems, rechargeable battery systems orgenerators are used as a power supply for the signal control section.

601-03-GB

3

230V

24VDC

TR

Transformer

G

Rectifier

C

Smoothing

T

Stabilisation

TFuse

50 °C

AC

Electrohydraulics Festo Didactic

Electrical circuitTitle

• A circuit consists of at least a power source, a load device andconnecting lines.

Notes

• Electrical current will flow only in a closed circuit.

• Technical direction of current flow: From the positive terminal of thepower supply to the negative terminal.

• A: Closed circuit without power supply.

• B: Introduction of a power supply to complete the circuit.

4

601-04-GB

A B

+

-

Electrohydraulics Festo Didactic

Measuring circuitsTitle

• Voltage and current measurements.Notes

• The voltage drop across a load device is measured in parallel withthe device.

• Electrical current is measured in series.

601-05-GB

5

+ +

- -

Voltage measurement Current measurement

V A

Electrohydraulics Festo Didactic

Ohm’s lawTitle

• Ohm’s law: Describes the relationship between current (I), voltage(V) and resistance (R).

Notes

• With ohmic resistances, the current rises in linear proportion to thevoltage.

• Graph: The value pairs for a constant resistance lie on a straightline. The current I is proportional to the voltage V.

• Mathematical formula for Ohm’s law:V = R · I or I = V / R.

601-06-GB

6

+A

VR

-

A2.0

1.5

1.0

0.5

0100 20

V

I

30 40V

Resistance R

Relay

V = R I·Solenoid coil

V

0.5 A 1 A 1.5 A 2 A

10 V 20 V 30 V 40 V

0.33 A 0.66 A 1 A 1.33 A

I = VR

Electrohydraulics Festo Didactic

RectifiersTitle

• Rectifiers convert AC to DC.Notes

• Diodes are conductive in only one direction.

• The polarity of the negative half-wave of the alternating voltage isreversed.

• The pulsating voltage is smoothed using a capacitor and filters(reactance coil, resistor).

601-07-GB

7

~

=

VV

t

V

tt

Diodes

Voltageretification

Voltagesmoothing

C R

L

Electrohydraulics Festo Didactic

Analogue, digital and binaryTitle

• Analogue values describe continuous functions, such as thecontinuous filling of a bucket of water.

Notes

• Digital values describe integer parts of a maximum value. A dice,for example, shows one of six possible numbers.

• Binary values are a special form of digital values. They can assumeonly two values, such as in the case of a switch, which can only beon or off.

601-08-GB

8

+

-

1

Experiments with dice

65432

0

Val

ue

Ligh

t

Time tSwitchingtime point

On 1

Off 0

full

half-full

emptyVol

ume

V

Filling time t

Electrohydraulics Festo Didactic

Momentary and sustained contact switchesTitle

• Actuation of contacts.Notes

• A momentary contact switch has a “rest position” and an “actuatedposition”.

• A sustained contact switch has two detents. It thus has two restpositions.

• Momentary and sustained switches can close or open current pathsor switch from one current path to another.

9

3 3

4 4

601-09-GB

Electrohydraulics Festo Didactic

N/O, N/C and changeover contactsTitle

• Example: Momentary-contact switch.Notes

• N/O: Contact normally open in rest position

• Changeover contact: N/O and N/C contacts in a single housing;one contact is open while the other is closed.

• The designations of the switch contacts are governed by theEuropean standard EN 50012.

3 1 4

Connection(N/O contact)

Switchelements

Connection(N/C contact)

4 2 1

2

601-10-GB

10 Electrohydraulics Festo Didactic

Limit switchesTitle

• Determining the position of a positioning slide.Notes

• Electrical contacts are actuated when a defined intermediate orend position is reached.

• Limit switches can be connected up as N/O, N/C or changeovercontacts.

601-11-GB

11

Switch lever

Stem(insulated)

Contact

Snap-action mechanism

Electrohydraulics Festo Didactic

Proximity switchesTitle

• Inductive: Signal is generated by the presence of any material withgood conductivity in an oscillating magnetic field.

Notes

• Capacitive: Signal is also generated by all insulators with highdielectric constants in an electrical field.

• Optical: Signal is generated when light barriers are interrupted orwhen light is reflected back to an optical sensor.

• Reed switches: Signal is generated by magnets whose fields closethe built-in contacts in the switch.

601-12-GB

12

Metal

MetalorInsulator

reflectivecomponent

inductive

capacitive

optical

Magnet

magnetic

Reed switch

Electrohydraulics Festo Didactic

Solenoid (electromagnet)Title

• A magnetic field with concentric field lines is created around aconductor carrying an electrical current.

Notes

• A coil carrying an electrical current develops a uniform magneticfield in its axial direction due to the overlapping of field lines.

• By appropriate alignment of elementary magnets, an iron core canbe made into a switchable electromagnet.

601-13-GB

13

Field arounda conductor

Coil

Iron core

+-

Electrohydraulics Festo Didactic

Electrohydraulic converters (solenoid valves)Title

• Convert electrical signals into hydraulic switching operations.Notes

• The switching armature is drawn into the coil, which acts as amagnet.

• This produces a displacement of the actuating piston in thehydraulic 4/2-way valve.

601-14-GB

14

BT A P

Switching armature

L

4/2-way solenoid valve

B

T

A

P

Electrohydraulics Festo Didactic

Dry and wet solenoidsTitle

• Dry solenoid: The solenoid is separated from the hydraulic fluid;a seal is required on the stem.

Notes

• Advantage of dry solenoids: Simple construction.

• Wet solenoid: The armature chamber of the solenoid is filled withhydraulic fluid, the solenoid operates in oil.

• Advantages of wet solenoid: Low friction, little abrasion, good heatdissipation, long service life.

601-15-GB

15

Dry solenoid Wet solenoid

seal

Electrohydraulics Festo Didactic

Solenoid valve connectionsTitle

• Connector components: Solenoid with plug base, cable withconnector socket.

Notes

• Electrical signals are transmitted via standard connectors.

• Advantage: Reliable alignment of connections which can beattached and detached quickly, protected against dust and water.

16

2

1

3

Protective earthconnection

Plug base

Electricalconnections

601-16-GB

Electrohydraulics Festo Didactic

Relays and contactorsTitle

• Definition: Switches which are actuated and held in their actuatedpositions electromagnetically.

Notes

• Used to separate control and power circuits.

• Special feature of relays:Hinged-armature design, single-break contacts, used for logic gatingof signals, (generally) changeover contacts.

• Special feature of contactors:Each main contact is of double-break type (contacts used as maincontacts), suitable for all power ratings from small to very large, onlyN/O and N/C contacts.

601-17-GB

+

+-

-

Contacts

CoilReturn spring Return springContacts

Coil Iron core Armature

Hinged-armature solenoid Plunger-armature solenoid

17 Electrohydraulics Festo Didactic

Direct and indirect activationTitle

• Direct activation: Connection of a solenoid valve via a switch (A).Notes

• Indirect activation: Connection of a solenoid valve via a relay (B).

• Advantage of indirect activation: Separation of control and powercircuits.

• The current passing through switch S1 (B) is lower, and the servicelife of the switch is significantly greater.

601-18-GB

3 33

4 44

24V 24V

0V 0V

1 1 2

S1S1 K1

Y1 Y1K1

A B

18 Electrohydraulics Festo Didactic

Signal inversionTitle

• The output signal is inversely proportional to the input signal.Notes

• A: Signal inversion at relay K1.

• B: Signal inversion at switch S1.

• The switching elements are shown under zero-voltage conditions.

601-19-GB

19

3 3

4 4

1 1

2 2

24V 24V

0V 0V

0 1

1 0

1 1

0 0

S1 S1K1 K1

0 0

1 1

Y1 Y1

1 12 2

A B

S1 S1K1 K1

Y1 Y1K1 K1

Electrohydraulics Festo Didactic

LatchingTitle

• Latching only with indirect activation.Notes

• Actuation of switch S1: Relay K1 reverses holding the current pathof K1 closed.

• The actuation of switch S2 interrupts the latched current path.

20

601-20-GB

3 3 3

4 4 4

1

2

1 2 324V

0V

S1

S2

K1

Y1K1

K1

dominant on

0

0

1

1

0

1

0

1

0

0

1

1

S1 S2 K1 & Y1

Electrohydraulics Festo Didactic

Circuit diagramTitle

• Lines of potential with constant voltage are drawn horizontally.Notes

• Current paths are drawn vertically and numbered consecutively.

• Circuit symbols are shown in the direction of current flow.

• Switching elements are generally shown under zero-voltageconditions.

• Latching to guard against sticking of relay contacts in current paths6 and 7.

601-21-GB

21

24V

0V

2 3 4 5

1

6 7

3

4

3

4

3

4

3

4

3

4

3

4

3

4

1

2

1

2

A1

A2

A1

A2

S1 K1

K1

S0

S2 K2 K1

K2

K2

K1

K2 Y1 Y2

Electrohydraulics Festo Didactic

Hydraulic power packTitle

• Hydraulic power pack for use in stationary hydraulic systems.Notes

• Power is delivered via the pressure medium using a pump anddrive motor.

• The pack incorporates devices to remove air, water and solidparticles from the hydraulic fluid.

601-22-GB

22

Baffle plate

Pressure relief valve(safety valve)

Hydraulic pump

Suction pipe

Suction filter

Return line

Air filter

Filler filter

Fluid levelindicator

Cleaningaperture

Drain screw

Pressure line

Electric motorn = 1500 rpm

Electrohydraulics Festo Didactic

Hydraulic circuitTitle

• Hydraulic systems consist of open or closed circuits.Notes

• Hydraulic fluid is used as an energy carrier.

• This energy is output via cylinders and motors.

• Relieved hydraulic fluid is returned to the tank or hydraulic pump.

601-23-GB

23

Hydrauliccylinder

Electrohydraulicpower valve

Safetyvalve

Hydraulicpump

Return line

Motor

Filter

Safety valves

Motor

Feed pump(top-up for leakage losses)

Hydraulicpump

Hydraulicmotor

open closed

M

M

Electrohydraulics Festo Didactic

Electrical and hydraulic powerTitle

• Electric motor:Driven by electric current on the basis of a potential difference.

Notes

• Electrical power is the product of voltage and current:P electr. = V • I (unit: watts).

• Hydraulic motor:Driven via fluid flow on the basis of a pressure difference.

• Hydraulic power is the product of pressure and flow rate:P hydr. = p • Q (unit: watts).

601-24-GB

24

P = V • Ielectr. P = p • qhydr.

Current I

Electric motor

Vol

tage

V

Pre

ssur

ep

Flow rate q

Gear motor

M+

-

Electrohydraulics Festo Didactic

Power lossesTitle

• Efficiency of electric motors:Frictional and magnetic losses.

Notes

• Efficiency of hydraulic pump:Frictional and volumetric losses.

• Valves, piping, tubing:Pressure losses dp, power losses expressed by P = ∆p • Q.

• Hydraulic motors and cylinders:Frictional and volumetric losses.

25

M M

Frictional andvolumetric losses

Frictional andpressure losses

Frictional,volumetric and

magnetic losses

P = p qhydr. loss ∆ l

Pow

erlo

sses

601-25-GB

Electrohydraulics Festo Didactic

Pressure switchesTitle

• Actuation of electrical contacts when a defined minimum pressure isreached.

Notes

• The minimum pressure (switching point) can be varied by means ofan adjustable spring.

• Example shows switching at approx. 4 bar with rising or fallingpressure.

• Generally connected up in practice as a changeover contact.

Switching point withrising pressure

Hysteresis

Switching point withfalling pressure

Symbolic representationin electrical circuit diagram

Symbolic representationin hydraulic circuit diagram

231

1

2 3

Pressurep

Time t

4 bar

pp

601-26-GB

26 Electrohydraulics Festo Didactic

4/3-way solenoid valveTitle

• Valve spool is directly actuated by solenoids.Notes

• Actuation on left: The piston spool is displaced to the right andcreates the connections P - A and B - T.

• Rest position produced by spring centring of piston spool. All inputsof the 4/3-way valve are closed in this position.

B

T

A

P

T A P B

a b

a b

T A P B

601-27-GB

27 Electrohydraulics Festo Didactic

4/3-way solenoid valve, pilotedTitle

• Direct activation of pilot spool via solenoids.Notes

• Actuation on left: The pilot piston spool is displaced to the right, andhydraulic fluid is directed to the right-hand side of the main controlspool, creating the connections P - A and B - T.

• Rest position produced by spring centring of pilot and main pistonspools. All ports of the 4/3-way valve are closed at the main valve.

601-28-GB

B

B

T

T

A

A

P

PPB AT

Simplified symbol

Detailed symbol

28 Electrohydraulics Festo Didactic

Electrical safetyTitle

• EMERGENCY STOP button placed in an easily accessible position.Notes

• Protection against voltages.

• Protection by means of insulation.

• Protection by means of earthed conductive housings.

• Safety isolation by means of transformers.

601-29-GB

29

1. Switch off2. Check3. Carry out work

EMERGENCYSTOP

Basic insulation

Additionalinsulation

N

L1

220 V AC 24 VPE

Safety insulation Protective earth Safety isolation

Electrohydraulics Festo Didactic

Hydraulic safetyTitle

• Safety regulations must be observed.Notes

• 1. Switch off motor/pump.2. Depressurise accumulator.3. Lower load.4. Check pressure.

• Work can now be carried out by authorised trained personnel.

601-30-GB

30

1. Switch offmotor/pump

2. Depressuriseaccumulator

4. Checkpressure

3. Lowerload

m

Electrohydraulics Festo Didactic