Guidelines for automating manufacturing systems with PLCs | EEP
Outputs to actuators allow a PLC to cause something to happen in a process. A short list of popular actuators is given below in order of relative popularity. Inputs come from sensors that translate physical phenomena into electrical signals. Typical examples of sensors are listed below in relative order of popularity. Sourcing and sinking inputs are also popular.
This output method dictates that a device does not supply any power. PNP is more popular.
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Industrial automation and control guides. Guidelines for automating manufacturing systems with PLCs. Continuous values seem more intuitive, but logical values are preferred because they allow more certainty, and simplify control.
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Continuous outputs require special output cards with digital to analog converters. Related EEP's content with sponsored links. Assume that the Boolean equation that describes the controller is already known. This equation can be converted into both a circuit diagram and ladder logic.
The circuit diagram contains about two dollars worth of integrated circuits.
Programmable logic controller
The prototype of the controller would cost thousands of dollars. Therefore a large number of circuit based controllers need to be produced before the break even occurs. This number is normally in the range of hundreds of units. There are some particular advantages of a PLC over digital circuits for the factory and some other applications.
The initial equation is not the simplest. It is possible to simplify the equation to the form seen in Figure If you are a visual learner you may want to notice that some simplifications are obvious with ladder logic - consider the C on both branches of the ladder logic in Figure The equation can also be manipulated to other forms that are more routine but less efficient as shown in Figure The equation shown is in disjunctive normal form - in simpler words this is ANDed terms ORed together.
This is also an example of a canonical form - in simpler terms this means a standard form. This form is more important for digital logic, but it can also make some PLC programming issues easier.
For example, when an equation is simplified, it may not look like the original design intention, and therefore becomes harder to rework without starting from the beginning. There are some common Boolean algebra techniques that are used when simplifying equations.
Recognizing these forms are important to simplifying Boolean Algebra with ease. These are itemized, with proofs in Figure Figure 67 Alternate Ladder Logic.
Automating Manufacturing Systems with PLCs
Figure 68 Reverse Engineering of a Digital Circuit. Eliminate NOTs that are for more than one variable. Eliminate complex functions such as EORs with their equivalent. Figure 70 The Simplified Form of the Example. Figure 71 A Canonical Logic Form. Figure 72 Common Boolean Algebra Techniques.
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