How a Ladder Logic diagram works?
In the ladder
The ladder program is written using a pictorial shape or symbol that is generally similar to a relay control circuit. The program is displayed on the screen with elements such as normally open contact, normally closed contact, timer, counter, sequencer etc.
displayed as in a pictorial form.
Under the right conditions, electricity can flow from the left-hand rail to the right-hand rail, a railroad track like this is called a ladder line.
The general rules in describing a ladder diagram are:
- Power flows from the left rail to the right rail
- The coil output cannot be connected directly to the left rail.
- No contacts are placed to the right of the coil output
- Only one coil output is allowed on the ladder line
Autocade simples for ladder logic:
The symbols displayed are given in an AutoCAD drawing for learners:
How to read a ladder logic program?
- Ladder diagrams are drawn vertically with inputs on the left and outputs on the right.
- Each rung of the ladder has output
- An individual output device can appear on the ladder diagram, read from left to right
- An individual physical input device (limit switch, push-button, pressure switch, etc.) may be used on the ladder diagram in both N.O. and N.C. configurations.
- Completing one rung, read the below rung as a continuation, till the end marked as stop.
- Internal contacts of the PLC are represented as conventional control relays and contacts.
- Control relay coils (outputs) appear on the ladder diagram.