Ladder Logic Symbols

Ladder elements

Contact

First of all, you have to know that ladder logic has contacts that make or break circuits to control coils. Each control coil or contact corresponds to the status of a single bit in the programmable controller’s memory. However, you can use these instructions to check if something is true, because they are conditional instructions. In the IECuino online ladder platform, you can use the blocks to draw your diagram.

NO (Normally Opened) Control Contact

Normally Opened Control
Symbol of Normally Opened Control

Usually, when we energize the coil or input that controls the open contact, it closes.
(Open contact at rest)

NC (Normally Closed) Control Contact

NC (Normally Closed) Contact
Symbol of Normally Closed Control

Generally, when we do not energize the coil or input that controls the NC contact, it closes. (Closed contact at rest)

Control Coil

Control Coil
Symbol of Control Coil

An output control coil is used to turn a bit on and off. The instruction itself even has a place in the PLC memory. Consequently, the PLC will show the result of the instruction. In general, inactive coil is energized whenever its rung is closed.
(Inactive at rest).

Pulse Timer

TP
Symbol of Pulse Timer

Pulse timers are used to produce a fixed-duration output from some initiating input. When there is an input to In 1 simultaneously there is an output from Out 1 and the timer starts. As a result, the timer contacts open when the predetermined time has elapsed.

On Delay Timer

TON
Symbol of On Delay Timer

At the moment that the ON delay timer is activated when the start input is TRUE. After the preset time expires, then the DONE output also goes TRUE. If at any time the start input goes FALSE the timer is reset and the done output goes to FALSE.

Off Delay Timer

TOF
Symbol Off Delay Timer

The Off Delay Timer instruction begins to count time base intervals when the rung makes a true to false transition. As long as rung conditions remain false, the timer increments its accumulated value (ACC) each scan until it reaches the preset value (PRE).

Up Counter

CTU
Symbol of Up Counter

Down Counter

CTD
Symbol of Down Counter

Firstly, we have to know that counters are used in many different applications. Some of them count from scratch and have a change in output status upon reaching a predetermined value; on the contrary, others count down from a preset value of zero to provide an exit status change.

However, some counters can operate in up and down counting mode, state of the state of an input pin of up / down counting mode.

Counters are synchronous, but are asynchronous presets. Four data inputs (A – D) allow loading the preset target. The counter decreases or increases synchronously with the low to high transition of the clock. Also, there is the high-speed mode for cascading the meters

The difference between an up and a down counter, of the ports that are connected to the display. For up counters, the non-inverted output, Q, is connected to the display. While for a downstream counter, the inverted output, nQ, is connected to the display.

You can take a look at the IECuino available tools ⚒️ to know more about the online ladder editor.

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