LD element contact

Symbol: , in the editor:

The element is only available in the LD editor.

A contact passes the signal TRUE (ON) or FALSE (OFF) from left to right, until the signal finally reaches a coil in the right part of the network. To this end, the contact is assigned a Boolean variable that contains the signal. To do this, replace the ??? placeholder above the contact with the name of a Boolean variable.

You can arrange several contacts in series or in parallel. If two parallel contacts are used, only one of them has to have the value TRUE for ON to be passed to the right. If contacts are connected in series, all contacts must be set to TRUE for ON to be passed to the right from the last contact of the series. You can therefore use LD to program electrical parallel and series circuits.

A negated contact passes on the signal TRUE if the variable value is FALSE. You can add an inserted contact by using the command Negation or a negated contact from the Toolbox view.

If you put the cursor on a contact in the selected network and press the left mouse button, the button Convert to Coil appears in the network. If you now move the cursor to this button with the mouse button held down and release the mouse button over the button, TwinCAT converts the contact into a coil.

See also:

• TC3 User Interface documentation: Command Negation
• TC3 User Interface documentation: Command Insert Contact
• TC3 User Interface documentation: Command Insert Negated Contact
• TC3 User Interface documentation: Command Insert Contact (right)
• TC3 User Interface documentation: Command Insert Contact Parallel (above)
• TC3 User Interface documentation: Command Insert Contact Parallel (below)