From the course: Learning PLC Ladder Logic: 1 The Basics

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Latch/unlatch example

Latch/unlatch example - Ladder Logic Tutorial

From the course: Learning PLC Ladder Logic: 1 The Basics

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Latch/unlatch example

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- [Instructor] So, now I'm going to use the same previous example of filling a tank and mixing the liquid, but instead I'm going to use a latch and unlatch instructions. Again, the example was there's a start pushbutton to start and filling valve opens to start filling the tank with the liquid. Once the liquid reaches a certain point, the valve closes and the mixer starts mixing until we press on the stop pushbutton. So, here we have three inputs and two outputs, and again, they're all normally open contacts. So, this is what we did, and once the start pushbutton is pressed, the valve is open and start filling. And as soon as you let go, the valve closes. So, in order to keep the valve open, previously we used a sealing instruction, or holding instruction, to keep the output on. This time we are going to use a latch instruction. Remember, latch instruction is an output instruction used to maintain or latch an output, even if the input condition changes. Any rung that has a latching…

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