Delta Electronics VFD-E Ladder Diagram Program Scan Chart of the PLC Ladder Diagram, Introduction

Appendix D How to Use PLC Function

D.3 Ladder Diagram

D.3.1 Program Scan Chart of the PLC Ladder Diagram

Calculate the result by ladder diagram algorithm (it doesn’t sent to the outer output point but the inner equipment will output immediately.)

Read input state from outside
	X0		X1
Start					Y0
	Y0
				X10
	M100 X3					Execute in cycles
					Y1
		:
		:
	X100 M505
					Y126
					End

Send the result to the output point

D.3.2 Introduction

Ladder diagram is a diagram language that applied on the automatic control and it is also a diagram that made up of the symbols of electric control circuit. PLC procedures are finished after ladder diagram editor edits the ladder diagram. It is easy to understand the control flow that indicated with diagram and also accept by technical staff of electric control circuit. Many basic symbols and motions of ladder diagram are the same as mechanical and electrical equipments of traditional automatic power panel, such as button, switch, relay, timer, counter and etc.

The kinds and amounts of PLC internal equipment will be different with brands. Although internal equipment has the name of traditional electric control circuit, such as relay, coil and contact. It doesn’t have the real components in it. In PLC, it just has a basic unit of internal memory. If this bit is 1, it means the coil is ON and if this bit is 0, it means the coil is OFF. You should read the corresponding value of that bit when using contact (Normally Open, NO or contact a). Otherwise, you should read the opposite sate of corresponding value of that bit when using contact (Normally Closed, NC or contact b). Many relays will need many bits, such as 8-bits makes up a byte. 2 bytes can make up a word. 2 words makes up double word. When using many relays to do calculation, such as add/subtraction or shift, you could

D-8 Revision June 2008, 04EE, SW--PW V1.11/CTL V2.11