ladder diagrams

LADDER DIAGRAMS

1. Introduction

It should be noted that while drawing any electrohydraulic (or electropneumatic) circuits, separate circuits should be drawn for the fluid system and the electrical system. Also each components should be labeled so that one can understand exactly how the two systems interfaced. The second circuit showing the electrical system is known as ladder diagram. Thus the operation of the total system can be understood by examination of both the fluid power circuit and ladder diagram (i.e., electrical circuit).

2. What is Meant by a Ladder Diagram?

• A ladder diagram is a representation of hardware connections between switches, relays, solenoids, etc., which constitute the basic components of an electrical control system.

• In other words, a ladder diagram is nothing but an electrical diagram showing the hardware connections between the various electrical control devices.

3. Details of a Ladder Diagram

Consider a typical ladder diagram as shown in Fig.14.9 for some application.

• Legs and Rungs: In Fig.14.9, the two vertical electrical power supply lines are called 'legs', and the horizontal lines containing electrical components are called 'rungs'.

• In ladder diagrams, always the power is connected to the left leg and the ground is connected to the right leg.

• It should be noted that always the switches should be shown in their unactuated (i.e., open) mode in the ladder diagrams.

• Since the electric circuit diagram resembles to a ladder, this diagram is called a 'ladder diagram'.

• Uses: Ladder diagrams provide a circuit designer with a practical means to examine input process and output functions to quickly plan the circuit layout design for a particular hydraulic or pneumatic application.

Now we shall illustrate some important electrohydraulic and electropneumatic circuits with the use of ladder diagrams.