Learning Learning System for Automation Automation and Communicat Communications ions
Electrohydraulics
Set of Overhead Transparencies Basic Level D.OT-TP601-GB 095051
Orde Orderr no.: no.: Designation: Designation: Descri Descriptio ption: n: Edition: Graphic Graphics: s: Layo Layout ut:: Author:
0950 095051 51 E.-HYDR. E.-HYDR. FOLIEN D.OT-T D.OT-TP601 P601-GB -GB 2 /96 T. Ocker, Ocker, D. Schwar Schwarzen zenber berger ger 23.2 23.2.9 .96, 6, M. Schw Schwar arz z D. Scholz
© Copyright by Festo Didactic KG, D-73734 Esslingen, 1996 All rights reserved, including translation rights. No part of this publication may be reproduced or transmitted in any form or by any means, electro electronic nic,, mechan mechanica ical, l, pho photoc tocopy opying, ing, or othe otherwi rwise, se, withou withoutt the prior prior written permission of Festo Didactic KG.
Festo Didactic
This set of overhead transparencies has been designed for use with the basic level of the technology package TP600 “Electrohydraulics”. The set of overhead transparencies and the technology package form part of Festo Didactic KG’s “Learning System for Automation and Communications”. The 30 transparencies in this set have been optimised from the didactic and methodological points of view. Each transparency is accompanied by a short text which provides the trainer with a quick overview of the training 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 electrical
circuit diagrams The text sheet includes a complete illustration of the transparency, in certain certain cases with additional explanations and legends which the trainer can enter on the transparency in the course of a training session. The advantages of this concept are: • The trainer can add to the transparenc transparencies ies step by step in the course course
of a training session. • The trainer is thus able to create a lively and interesting atmosphere. • The provision of accompanying text means less preparation work for
the trainer.
601 60 1
Introduction
Festo Didactic
601
Contents
Electrohydraulic press . . . . . . . . . . . . . . . . . . . . . . . . . . . Transparency 1 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
1
Electrohydraulics
Festo Didactic
Title
Electrohydraulic press
Notes
• Function units: Motor with hydraulic pump, control panel, valve
manifold, cylinder. • The hydraulic press is controlled via the electrical control panel. • Electrical signals are used to activate the valves in the hydraulic
installation. • The electrohydraulic press is used to form rectangular troughs.
Motor with hydraulic pump
Valve manifold
Actuator (cylinder)
Control panel
601-01-GB
2
Electrohydraulics
Festo Didactic
Title
Schematic Schematic layout layout of an electrohydrau electrohydraulic lic installatio installation n
Notes
• Division of installation into signal control section and hydraulic
power section. • Signal control section: Input and processing of electrical signals. • Solenoid valves form the interface between the electrical signal
control section and the hydraulic power section. • Hydraulic power section: Controls the flow of hydraulic fluid by
means of solenoid valves. Actuators convert hydraulic energy into motions.
Power section Signal control section
Signal input
Signal processing
Hydraulic cylinder
Solenoid valve
Power supply
601-02-GB
Hydraulic power supply (conversion)
3
Electrohydraulics
Festo Didactic
Title
Electrical power supply unit
Notes
• Connection to mains supply. • Supplies signal control section with specified or maximum voltage
and current values. • Functions in power supply unit: Voltage transformation, rectification,
smoothing, stabilisation, fuse protection. • In mobile hydraulic systems, rechargeable battery systems or
generators are used as a power supply for the signal control section.
230V AC DC 24V
50 °C
TR Transformer
601-03-GB
G Rectifier
C
T
Smoothing Stabilisation
T Fuse
4
Electrohydraulics
Festo Didactic
Title
Electrical circuit
Notes
• A circuit consists of at least a power source, a load device and
connecting lines. • Electrical current will flow only in a closed circuit. • Technical direction of current flow: From the positive terminal of the
power supply to the negative terminal. • A: Closed circuit without power supply. • B: Introduction of a power supply to complete the circuit.
A
B
+
-
601-04-GB
5
Electrohydraulics
Festo Didactic
Title
Measuring circuits
Notes
• Voltage and current measurements. • The voltage drop across a load device is measured in parallel with
the device. • Electrical current is measured in series.
+
-
+ V
Voltage measurement
601-05-GB
-
A
Current measurement
6
Electrohydraulics
Festo Didactic
Title
Ohm’s law
Notes
• Ohm’s law: Describes the relationship between current (I), voltage
(V) and resistance (R). • With ohmic resistances, the current rises in linear proportion to the
voltage. • Graph: The value pairs for a constant resistance lie on a straight
line. The current I is proportional to the voltage V. • Mathematical formula for Ohm’s law:
V = R · I or I = V / R.
V
Resistance R
10 V
20 V
30 V
40 V
Relay
0.5 A
1A
1.5 A
2A
Solenoid coil
0.33 A 0.66 A
1A
1.33 A
V=R·I I=
+
V R
2.0 A 1.5
A R
-
1.0
V
I
0.5 0
0
10
20 V
601-06-GB
30 V 40
7
Electrohydraulics
Festo Didactic
Title
Rectifiers
Notes
• Rectifiers convert AC to DC. • Diodes are conductive in only one direction. • The polarity of the negative half-wave of the alternating voltage is
reversed. • The pulsating voltage is smoothed using a capacitor and filters
(reactance coil, resistor).
L
~ C
Diodes
Voltage retification
V
601-07-GB
Voltage smoothing
V
t
=
R
V
t
t
8
Electrohydraulics
Festo Didactic
Title
Analogue, digital and binary
Notes
• Analogue values describe continuous functions, such as the
continuous filling of a bucket of water. • 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 assume
only two values, such as in the case of a switch, which can only be on or off.
+
-
full
V e half m u full l o V empty
e u l a V
Filling time t
601-08-GB
6 5 4 3 2 1 0
Experiments with dice
On 1 t h g i L
Off 0
Switching time point
Time t
9
Electrohydraulics
Festo Didactic
Title
Momentary and sustained contact switches
Notes
• Actuation of contacts. • A momentary contact switch has a “rest position” and an “actuated
position”. • A sustained contact switch has two detents. It thus has two rest
positions. • Momentary and sustained switches can close or open current paths
or switch from one current path to another.
601-09-GB
3
3
4
4
10
Electrohydraulics
Festo Didactic
Title
N/O, N/C and changeover contacts
Notes
• Example: Momentary-contact switch. • 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 the
European standard EN 50012.
Switch elements
601-10-GB
3
1
4
2
Connection (N/O contact)
2
4 1
Connection (N/C contact)
11
Electrohydraulics
Festo Didactic
Title
Limit switches
Notes
• Determining the position of a positioning slide. • Electrical contacts are actuated when a defined intermediate or
end position is reached. • Limit switches can be connected up as N/O, N/C or changeover
contacts.
Switch lever
Contact
Stem (insulated)
Snap-action mechanism
601-11-GB
12
Electrohydraulics
Festo Didactic
Title
Proximity switches
Notes
• Inductive: Signal is generated by the presence of any material with
good conductivity in an oscillating magnetic field. • Capacitive: Signal is also generated by all insulators with high
dielectric constants in an electrical field. • Optical: Signal is generated when light barriers are interrupted or
when light is reflected back to an optical sensor. • Reed switches: Signal is generated by magnets whose fields close
the built-in contacts in the switch.
inductive
capacitive
optical
601-12-GB
Metal
Metal or Insulator
reflective component
Reed switch
Magnet
magnetic
13
Electrohydraulics
Festo Didactic
Title
Solenoid (electromagnet)
Notes
• A magnetic field with concentric field lines is created around a
conductor carrying an electrical current. • A coil carrying an electrical current develops a uniform magnetic
field in its axial direction due to the overlapping of field lines. • By appropriate alignment of elementary magnets, an iron core can
be made into a switchable electromagnet.
Field around a conductor Iron core
+
-
Coil
601-13-GB
14
Electrohydraulics
Festo Didactic
Title
Electrohydraulic converters (solenoid valves)
Notes
• Convert electrical signals into hydraulic switching operations. • The switching armature is drawn into the coil, which acts as a
magnet. • This produces a displacement of the actuating piston in the
hydraulic 4/2-way valve.
Switching armature
A
B
P
T
4/2-way solenoid valve T A P B
601-14-GB
L
15
Electrohydraulics
Festo Didactic
Title
Dry and wet solenoids
Notes
• Dry solenoid: The solenoid is separated from the hydraulic fluid;
a seal is required on the stem. • Advantage of dry solenoids: Simple construction. • Wet solenoid: The armature chamber of the solenoid is filled with
hydraulic fluid, the solenoid operates in oil. • Advantages of wet solenoid: Low friction, little abrasion, good heat
dissipation, long service life.
seal
Dry solenoid
601-15-GB
Wet solenoid
16
Electrohydraulics
Festo Didactic
Title
Solenoid valve connections
Notes
• Connector components: Solenoid with plug base, cable with
connector socket. • Electrical signals are transmitted via standard connectors. • Advantage: Reliable alignment of connections which can be
attached and detached quickly, protected against dust and water.
2 3 1
Electrical connections Protective earth connection Plug base
601-16-GB
17
Electrohydraulics
Festo Didactic
Title
Relays and contactors
Notes
• Definition: Switches which are actuated and held in their actuated
positions electromagnetically. • Used to separate control and power circuits. • Special feature of relays:
Hinged-armature design, single-break contacts, used for logic gating of signals, (generally) changeover contacts. • Special feature of contactors:
Each main contact is of double-break type (contacts used as main contacts), suitable for all power ratings from small to very large, only N/O and N/C contacts.
Coil Iron core
Armature
Contacts
+ +
-
Return spring
Contacts
Hinged-armature solenoid
601-17-GB
Return spring
Coil
Plunger-armature solenoid
18
Electrohydraulics
Festo Didactic
Title
Direct and indirect activation
Notes
• Direct activation: Connection of a solenoid valve via a switch (A). • Indirect activation: Connection of a solenoid valve via a relay (B). • Advantage of indirect activation: Separation of control and power
circuits. • The current passing through switch S1 (B) is lower, and the service
life of the switch is significantly greater.
A
B
1
24V
1
24V
3
3
S1
S1 4
4
Y1
0V
601-18-GB
2
K1
0V
3
K1
Y1
4
19
Electrohydraulics
Festo Didactic
Title
Signal inversion
Notes
• The output signal is inversely proportional to the input signal. • A: Signal inversion at relay K1. • B: Signal inversion at switch S1. • The switching elements are shown under zero-voltage conditions.
A
B
1
24V
2
3
1
3
S1
4
2
K1
4
2
Y1
K1
0V
601-19-GB
2
1
K1
S1
K1
1
24V
Y1
0V S1
K1
Y1
S1
K1
Y1
0
0
1
0
1
1
1
1
0
1
0
0
20
Electrohydraulics
Festo Didactic
Title
Latching
Notes
• Latching only with indirect activation. • Actuation of switch S1: Relay K1 reverses holding the current path
of K1 closed. • The actuation of switch S2 interrupts the latched current path.
1
24V
2
3
3
3
S1
K1 4
S2 2
0V
601-20-GB
S1
S2
K1 & Y1
4
0
0
0
0
1
0
1
0
1
1
1
1
K1 4 1
K1
3
Y1
dominant on
21
Electrohydraulics
Festo Didactic
Title
Circuit diagram
Notes
• Lines of potential with constant voltage are drawn horizontally. • 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-voltage
conditions. • Latching to guard against sticking of relay contacts in current paths
6 and 7.
24V
1 3
S0 4
3
2
3
S1
4
3
K1
5
4
4
3
S2
4
6
3
K2
4
7
3
K1
4
3
K2
1
K2
1
K1 2
A1
K1 A2
0V
601-21-GB
2
A1
K2
Y1 A2
4
Y2
22
Electrohydraulics
Festo Didactic
Title
Hydraulic power pack
Notes
• Hydraulic power pack for use in stationary hydraulic systems. • Power is delivered via the pressure medium using a pump and
drive motor. • The pack incorporates devices to remove air, water and solid
particles from the hydraulic fluid.
Pressure line Pressure relief valve (safety valve)
Return line Air filter
Hydraulic pump Filler filter Electric motor n = 1500 rpm Fluid level indicator Suction pipe Cleaning aperture
Suction filter Baffle plate
Drain screw
601-22-GB
23
Electrohydraulics
Festo Didactic
Title
Hydraulic circuit
Notes
• Hydraulic systems consist of open or closed circuits. • 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.
Hydraulic cylinder Safety valves
Electrohydraulic power valve
Hydraulic pump Safety valve
Hydraulic motor
Motor Motor
M Filter
M Return line
Hydraulic Feed pump pump (top-up for leakage losses)
open
601-23-GB
closed
24
Electrohydraulics
Festo Didactic
Title
Electrical and hydraulic power
Notes
• Electric motor:
Driven by electric current on the basis of a potential difference. • 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).
Pelectr. = V•I
Phydr. = p • q
Current I
Flow rate q
V e g a t l o V
+ M
-
p e r u s s e r P
Electric motor Gear motor
601-24-GB
25
Electrohydraulics
Festo Didactic
Title
Power losses
Notes
• Efficiency of electric motors:
Frictional and magnetic losses. • 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.
Frictional and volumetric losses s e s s o l r e w o P
Frictional and pressure losses
M
Frictional, volumetric and magnetic losses
Phydr. loss = ∆p
601-25-GB
q
l
M
26
Electrohydraulics
Festo Didactic
Title
Pressure switches
Notes
• Actuation of electrical contacts when a defined minimum pressure is
reached. • The minimum pressure (switching point) can be varied by means of
an adjustable spring. • Example shows switching at approx. 4 bar with rising or falling
pressure. • Generally connected up in practice as a changeover contact.
2 3
Symbolic representation in hydraulic circuit diagram
p
Symbolic representation in electrical circuit diagram
p 1
1 3 2
Switching point with rising pressure
Switching point with falling pressure
Pressure p 4 bar
Hysteresis
Time t
601-26-GB
27
Electrohydraulics
Festo Didactic
Title
4/3-way solenoid valve
Notes
• Valve spool is directly actuated by solenoids. • Actuation on left: The piston spool is displaced to the right and
creates the connections P - A and B - T. • Rest position produced by spring centring of piston spool. All inputs
of the 4/3-way valve are closed in this position.
A
B
P
T
a
T
A
P
B
a
b
T
601-27-GB
b
A
P
B
28
Electrohydraulics
Title
4/3-way solenoid valve, piloted
Notes
• Direct activation of pilot spool via solenoids.
Festo Didactic
• Actuation on left: The pilot piston spool is displaced to the right, and
hydraulic fluid is directed to the right-hand side of the main control spool, creating the connections P - A and B - T. • Rest position produced by spring centring of pilot and main piston
spools. All ports of the 4/3-way valve are closed at the main valve.
A
B
P
T
Simplified symbol
T
B
P
A
A
B
P
T
Detailed symbol
601-28-GB
29
Electrohydraulics
Festo Didactic
Title
Electrical safety
Notes
• EMERGENCY STOP button placed in an easily accessible position. • Protection against voltages. • Protection by means of insulation. • Protection by means of earthed conductive housings. • Safety isolation by means of transformers.
1. Switch off 2. Check 3. Carry out work EMERGENCY STOP
Safety insulation
Protective earth
Safety isolation
Additional insulation
L1 PE
220 V AC
N Basic insulation
601-29-GB
24 V
