1 · Web viewIntroduction Of Automation: Automation (ancient Greek: = self dictated), roboticization or industrial automation or numerical control is the use of control systems such

INTRODUCTION TO AUTOMATION SYSTEM

Introduction Of Automation:

Automation (ancient Greek: = self dictated), roboticization or industrial automation or numerical control is the use of control systems such as computers to control industrial machinery and processes, replacing human operators. In the scope of industrialization, it is a step beyond mechanization. Whereas mechanization provided human operators with machinery to assist them with the physical requirements of work, automation greatly reduces the need for human sensory and mental requirements as well. Processes and systems can also be (automated).

Automation plays an increasingly important role in the global economy and in daily experience. Engineers strive to combine automated devices with mathematical and organizational tools to create complex systems for a rapidly expanding range of applications and human activities.

Definition of automation:

Automated Control System is a system that is capable of controlling a process with minimal human assistance or without human and have the ability to start, to adjust, to display or to measure variables in the process and stop the process in order to obtainthe desired output.

It is a technology dealing with the application of: mechatronics computers

for production of goods and services.

Automation is broadly classified into manufacturing automation service automation

Examples:Robots, CNC machine tools, ASRS, security systems, CAD/CAM systems, logistics support tools, automated inspection systems, material handling systems, etc.

Purpose: increase productions quality improve productions quality cost control

Type Of Automation

Fixed automation Programmable automation Flexible automation

a. Fixed/Hardwired automation custom-engineered, special-purpose equipment to automate a fixed

sequence of operations high production rates, inflexible product design

Functions of control circuit is fixed and permanent Work will be complicated if we want to do other work other than the

existing task on this type of control system.

b. Programmable automation equipment designed to accommodate a specific class of product changes

batch production, medium volume

Functions of control circuit programmed by the user and may be modified When the task to be performed by machines changed, the

changes only needs to be done by making modifications to control program instead of modify the circuit.

c. Flexible automation designed to manufacture a variety of products or parts

low production rates, varying product design and demand

Fixed Automation dual torch welding lathe cell simultaneously welding two flanges onto an automotive catalytic converter

Flexible Automation robotic cell welding automotive engine cradle assembly

HI-Star Model 25

Economically priced, XYZ, programmable automation systems. Work envelope of 25 inches by 24 inches, with 6 inches of Z axis.

Rigid platform for a variety of path oriented applications.

Attributes and advantagesAutomation When to consider Advantages DisadvantagesFixed High demand

volume, longproduct life cycles

• maximumefficiency• low unit cost

• large initialinvestment• inflexibility

Programmable Batch production,products withdifferent options

• flexibility to dealwith changes inproduct• low unit cost forlarge batches

• new productrequires long setup time• high unit costrelative to fixedautomation

Flexible Low productionrates, varyingdemand, shortproduct life cycles

• flexibility to dealwith designvariations• customizedproducts

• large initialinvestment• high unit costrelative to fixedor programmableautomation

Fixed: GE 1.5 billion light bulbs per year Programmable: CNC machines used in batch production Flexible: Honda (113 motorcycle models in 18 months)

Production Volume and Variety

Comparison between Fix and programmable automation:

Fix Automation Programmable Automation

UseSpecific Varius

Easy to make changes/improvements

difficult Easy

Maintenancedifficult Easy

AbilityDepending on the

design and manufacture

Very high

Speed slow fast

Efficiency Suitable for small

systemsSuitable for all

systems

RELAY

Introduction

Relays are simple switches which are operated both electrically and mechanically. Relays consist of an electromagnet and also a set of contacts. The switching mechanism is carried out with the help of the electromagnet. There are

also other operating principles for its working. But they differ according to their applications. Most of the devices have the application of relays.

The main operation of a relay comes in places where only a low-power signal can be used to control a circuit. It is also used in places where only one signal can be used to control a lot of circuits. The application of relays started during the invention of telephones. They played an important role in switching calls in telephone exchanges. They were also used in long distance telegraphy. They were used to switch the signal coming from one source to another destination. After the invention of computers they were also used to perform Boolean and other logical operations. The high end applications of relays require high power to be driven by electric motors and so on. Such relays are called contactors.

a. Symbol

Relay symbols commonly used are:

b. Building diagram

In general, a relay consists of a magnetic core and its associated coil, contacts, springs, armature, and the mounting. Figure 1.0 illustrates the construction of a relay.

Figure 1.0 —Relay construction.

A relay can have many different types of contacts. The relay shown in figure 1.0 has contacts known as "break-make" contacts because they break one circuit and make another when the relay is energized. Figure 1.1 shows five different combinations of relay contacts and the names given to each.

Figure 1.1 : Contact

combination

c. Operation

Refer to figure 1.0, when the coil is energized, the flow of current through the coil creates a strong magnetic field which pulls the armature downward to contact C1,completing the circuit from the common terminal to C1. At the same time, the circuit to contact C2, is opened. Figure 1.2 shows a SPST relay used to control ac load.

Figure 1.2 : SPST relay used to control a ac load

In the above schematic, the relay's coil is energized by the low-voltage (12 VDC) source, while the single-pole, single-throw (SPST) contact interrupts the high-voltage (480 VAC) circuit. It is quite likely that the current required to energize the relay coil will be hundreds of times less than the current rating of the contact. Typical relay coil currents are well below 1 amp, while typical contact ratings for industrial relays are at least 10 amps.

d. Various types of relay (SPDT, DPDT, 4PDT)

Since relays are switches, the terminology applied to switches is also applied to relays. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways:

Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact.

Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact.

Change-over (CO), or double-throw (DT), contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact ("break before make"). If this type of contact utilizes a "make before break" functionality, then it is called a Form D contact.

The following designations are commonly encountered:

SPST - Single Pole Single Throw. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.

SPDT - Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

DPST - Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. The poles may be Form A or Form B (or one of each).

DPDT - Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.

The "S" or "D" may be replaced with a number, indicating multiple switches connected to a single actuator. For example 4PDT indicates a four pole double throw relay (with 14 terminals).

Fig. 1.0: Circuit symbols of relays.  Fig. 1.1: The package of a DPDT AC coil relay

Figure 1.0 shown Circuit symbols of relays. "C" denotes the common terminal in SPDT and DPDT types while, the Figure 1.1 shown The diagram on the package of a DPDT AC coil relay

e. Application examples

Relays are used to and for:

Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers.

Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile,

Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),

Isolate the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors in an effort to conserve energy,

Logic functions. For example, the boolean AND function is realised by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using normally closed contacts. The Ladder programming language is often used for designing relay logic networks.

Early computing. Before vacuum tubes and transistors, relays were used as logical elements in digital computers. See ARRA (computer), Harvard Mark II, Zuse Z2, and Zuse Z3.

Safety-critical logic. Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery.

Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. A very short (a fraction of a second) delay would use a copper disk between the armature and moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed.

A DPDT AC coil relay with "ice cube" packaging

Examples of the use of relay:

i. Electrical Circuit (automobile)

ii. Electric/electronic circuit. (DC to AC)

iii. Motor control circuit