CHAPTER 1.0: INTRODUCTION TO AUTOMATION SYSTEM

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1 CHAPTER 1.0: INTRODUCTION TO AUTOMATION SYSTEM 1.1. Introduce types of automation in industry Definition of automation system. Is a technology dealing with the application of mechatronics and computers for production of goods and services. Automation is broadly classified into manufacturing automation and service automation Types of automation system 1) Fixed automation Custom-engineered, special-purpose equipment to automate a fixed sequence of operations. High production rates, inflexible product design. 2) Programmable automation equipment designed to accommodate a specific class of product changes batch production, medium volume 3) Flexible automation Designed to manufacture a variety of products or parts. Low production rates, varying product design and demand Comparison between Fixed / Programmable / Flexible automation

2 1.2. Understand relays, contactors, electromechanical timer and electromechanical counter Relays A relay is used to isolate one electrical circuit from another. It allows a low current control circuit to make or break an electrically isolated high current circuit path a) Symbol: The relay's switch connections are usually labeled COM, NC and NO: COM = Common, always connect to this; it is the moving part of the switch. NC = Normally Closed, COM is connected to this when the relay coil is off. NO = Normally Open, COM is connected to this when the relay coil is on. b) Relays Operation All relays operate using the same basic principle. For this example will use a commonly used 4 pin relay. Relays have two circuits: A control circuit (shown in GREEN) and a load circuit (shown in RED). The control circuit has a small control coil while the load circuit has a switch. The coil controls the operation of the switch. RELAY ENERGIZED (ON) Current flowing through the control circuit coil (pins 1 and 3) creates a small magnetic field which causes the switch to close, pins 2 and 4. The switch, which is part of the load circuit, is used to control an electrical circuit that may connect to it. Current now flows through pin 2 and 4 shown in RED, when the relay in energized.

3 RELAY DE-ENERGIZED (OFF) When current stops flowing through the control circuit, pins 1 and 3, the relay becomes de- energized. Without the magnetic field, the switch opens and current is prevented from flowing through pins 2 and 4. The relay is now OFF RELAY OPERATION When no voltage is applied to pin 1, there is no current flow through the coil. No current means no magnetic field is developed, and the switch is open. When voltage is supplied to pin 1, current flow though the coil creates the magnetic field needed to close the switch allowing continuity between pins 2 and 4

4 d) Various types of relay This is a Single Pole Single Throw (SPST) relay. Current will only flow through the contacts when the relay coil is energized. This is a Single Pole Double Throw (SPDT) relay. Current will flow between the movable contact and one fixed contact when the coil is DE-energized and between the movable contact and the alternate fixed contact when the relay coil is energized. This is a Double Pole Single Throw (DPST) relay. When the relay coil is energized, two separate and electrically isolated sets of contacts are pulled down to make contact with their stationary counterparts. There is no complete circuit path when the relay is DEenergized. This relay is a Double Pole Double Throw (DPDT) relay. It operates like the SPDT relay but has twice as many contacts. There are two completely isolated sets of contacts. This is a 4 Pole Double Throw (4PDT) relay. It operates like the SPDT relay but it has 4 sets of isolated contacts. e) Application Examples Relays are quite common in home appliances where there is an electronic control turning on something like a motor or a light. They are also common in cars, where the 12V supply voltage means that just about everything needs a large amount of current.

5 1.2.2 Contactors Contactors are used to indicate an open or closed path of current flow. Contacts are shown as normally open (NO) or normally closed (NC). Contacts shown by this symbol require another device to actuate them. a) Symbol b) Operation Normally Open Contact In the following illustration the circuit is first shown in the de-energized state. The contacts are shown in their normally open (NO) state. When the relay is energized, the contacts close, completing the path of current and illuminating the light. The contacts have been highlighted to indicate they are now closed. Normally Close Contact In the following illustration the contacts are shown as normally closed (NC), meaning the contacts is closed when the relay is de-energized. A complete path of current exists and the light is on. When the relay is energized, the contacts open turning the light off.

6 c) Building Diagram Difference between Contactor and Relay Since a contactor is required for a higher load, a relay is always cheaper than a contactor. A relay is normally used in appliances below 5KW, while a contactor is preferred when the appliance is heavier. A relay is used only in control circuit while a contactor can be used in both control and power circuits. In general contactors are little slower than relays Contactor is so designed that it can be repaired while it is not normally done in the case of relays.

7 Coil Coils are used in electromagnetic starters, contactors, and relays. The purpose of contactors and relays is to open and close associated contacts. Contactors and relays use an electromagnetic action to open and close these contacts. a) Symbol b) Operation The M contacts in series with the motor are controlled by the M contactor coil. When someone closes the switch, a complete path of current flow exists through the switch and M contactor coil. The M contactor coil actuates the M contacts which provide power to the motor Electromechanical Timer Electromechanical counters and electromechanical timers typically accept electric or electronic inputs to operate a mechanical display, such as rotating wheels or knobs. A counter is a complete instrument for detecting, totalizing, and indicating a sequence of events. A timer is a device for automatically starting, or stopping a machine or other device. Many of these instruments can perform both counter and timer functions. Electromechanical counters and electromechanical timers can be either single function or multi function, or programmable for more than one function.

8 Symbol Contact symbols determine the time of timer action:- On-delay action - TR energized, contacts change state after set time interval Off-delay action - TR de-energized, contacts change state after set time interval Electromechanical Counter Symbol : Operation : Electromechanical counters and electromechanical timers can be up direction, down direction, or bidirectional. Up directional counters can advance forward (UP) in its counting sequence. Down directional counters can advance backward (DOWN) in its counting sequence. A bi-directional counter can advance forward or backward (UP or DOWN) in its counting sequence.