5-Ladder Diagram and FBD.pptx...........

Ladder diagram and FBD diagram

1. Chapter 5 Ladder and Functional Block Programming PROGRAMMABLE LOGIC CONTROLLER

2. PLC Ladder Programming PROGRAMMABLE LOGIC CONTROLLER A very commonly used method of programming PLCs is based on the use of ladder diagrams . The ladder diagram consists of two vertical lines representing the power rails. Circuits are connected as horizontal lines, that rungs the ladder, between these two verticals.

3. PROGRAMMABLE LOGIC CONTROLLER In drawing ladder diagram, certain conventions are adopted: The vertical lines of diagram represent the power rails between which circuits are connected. Each rung on the ladder defines one operation in the control process. A ladder diagram is read from left to right and from top to bottom. Each rung must start with an input and must end with at least one output. Electrical devices shown In their normal condition. Thus, a switch is normally open until some objects closes it. A particular device can appear in more than one rung of a ladder. The input and outputs are all identified by their addresses, the notation used depends on the PLC manufacturer.

4. PROGRAMMABLE LOGIC CONTROLLER PLC, normally start with an input, we have open symbol | | for input contacts. The line terminates with the output, denoted by the symbol ( ). In drawing ladder diagrams the names of associated variable or addresses of each element depends on each symbol and manufacturer.

5. AND PROGRAMMABLE LOGIC CONTROLLER In AND operations output is not energized unless two, normally open, switches are both closed. Switch A and switch B have both to be closed, which thus gives an AND logic situation.

6. OR PROGRAMMABLE LOGIC CONTROLLER In OR operations, output is energized when switch A or B, both normally open, are closed. Input A or input B must be on for there to be an output.

7. NOT PROGRAMMABLE LOGIC CONTROLLER When there is an input to the switch, it opens and there is no current in the circuit. In NOT operation, there is an output when there is no input and no output when there is an input. The gate is sometimes referred to as inverter.

8. NAND PROGRAMMABLE LOGIC CONTROLLER The consequence of having the NOT gates is to invert all the outputs from the AND gate. An alternative, which gives exactly the same result, is to put a NOT gate on each input and then follow with OR. Both the inputs A and B have to be 0 for there to be 1 output. There is an output when input A and input B are not 1.

9. NOR PROGRAMMABLE LOGIC CONTROLLER The consequence of having the NOT gates is to invert all the outputs from the OR gate. An alternative, which gives exactly the same result, is to put a NOT gate on each input and then follow with AND. There is an output when neither input A or input B is 1.

10. EXCLUSIVE OR(XOR) PROGRAMMABLE LOGIC CONTROLLER One way of obtaining an exclusive or (XOR) operation is by using NOT, AND or OR gates.

11. Latching PROGRAMMABLE LOGIC CONTROLLER The term latch circuit is used for the circuit used to carry out such operation. It is a self-maintaining circuit in that, after being energized, it maintains that state until another input is received. Latching is widely used with start-ups so that the initial switch on of an application becomes latched on.

12. Multiple Outputs PROGRAMMABLE LOGIC CONTROLLER With ladder diagrams, there can be more than one output connected to a contact.

13. Function Blocks PROGRAMMABLE LOGIC CONTROLLER The term function block diagram (FBD) is used for PLC programs described in terms of graphical blocks. It is a graphical language for depicting signals and data flows through blocks, these being reusable software elements.