Monday, July 4, 2011

Tutorial Latching Using an Internal Relay





In this article it will involve Internal Relays and also bring in the symbol of LOADBAR. The TEP PLC software knowledge is understood. An Internal Relay can be consideration of as virtual relay within the PLC. The symbol of OUT can be utilized to modify the Internal Relay state and the symbol of LOAD can be applied to read the state.

In the follow case, it will exploit an Internal Relay to form a latch.
• Make a new document of Ladder Logic.
• Put two symbols of LOAD, a symbol of OUT and join them.
• Click the right button of mouse on the top LOAD symbol and choose INPUT1.
• Click the right button of mouse on the symbol of OUT and choose INTERNAL1 from the submenu of Internal Relays.
• Click the right button of mouse on the symbol of lower LOAD and choose INTERNAL1.

When the above program of Ladder Logic is work, to start with the internal relay, which INTERNAL1 is turn off. There is no right symbols path to the OUT, if then INPUT1 is also turn off symbol. The symbol of LOAD INPUT1 is right, if INPUT1 is on, there is a true symbols path to the symbol of OUT and INTERNAL1 is turned on. When INTERNAL1 is on, there will always be a path to the symbol of OUT throughout the symbol of LOAD INTERNAL1 and INTERNAL1 will stay on.

Before it can trial this program it needs to add another Ladder Logic rung to demonstrate the INTERNAL1 state on an output.
• Duplicate the second rung.
• Transfer the program to the PLC. You should discover that OUTPUT1 turns into latched on when the button of INPUT1 is pressed.

Now it will bring in the new symbol that is identified as LOADBAR. The symbol of LOADBAR is alike to the symbol of LOAD except its states of true and false are conversed. If LOADBAR loads a something state that is on, it will get on a vice versa and false value. To put in a reset feature to the program, it needs to break the true symbols path formed by the condition of latch.
• When INPUT2 is off, Put in a symbol of LOADBAR and set it to load INPUT2, the symbol of LOADBAR is true and the path throughout either symbol of LOAD is not broke off. If INTERNAL1 is on and INPUT2 is switched on, the true symbols path is broke off by the false symbol of LOADBAR and INTERNAL1 is switched off.
• Transfer the program to the PLC and examine the behavior.



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