Program logic controler

This graphical language has been around since the dawn of modern PLCs in the early s , first used because it borrowed from the relay diagrams with which plant electricians were already familiar. Now, the number of available symbols has grown over time, leading to more advanced and diverse functionalities.

The PLC relies on these symbols to simulate real-world relay logic controls, connecting them through lines of circuitry and power to direct the flow of the electrical current. Often called ladder logic , ladder programming gets its name because the code that results assembles a ladder, comprised of the following symbols:.

While ladder logic is a full language of symbols, there are some that you will see more than others, especially in diagrams.

A light switch is an example of a NO circuit, as it stays off unless someone turns it on. Other uses for the NO symbol include power buttons and other internal programmers. On the other hand, an NC contact represents a circuit that remains active until an input triggers a shutdown. The output symbol is a common representation for warning signs, indicator lights, and motor contactors.

The output for each turns on when the corresponding input becomes energized. Timer instructions allow for on-delayed or off-delayed events. A Timer Delay-On system begins a timer to turn the system on when the PLC input energizes, giving it time to warm up before operation. This works well for delaying siren sounds and facilitating sequence start delays. A Timer Delay-Off system puts this delay at the end of operation, allowing for time to pass between the shut-off operation and the actual system shutdown.

This system will determine if a given value is greater than, less than, or equal to another value. One application is in batching systems, which will use comparisons to ensure that all package components are the same weight. Math instructions or calculators enable simple addition and subtraction functions, allowing PLCs to calculate data such as motor speed. In addition to these typical numerical functions, they can also power more complex transcendental functions such as square roots, as well as trigonometric sine, cosine, and tangents along with their inverse forms arc sine, arc cosine, and arc tangent.

Advanced instructions may include communication directions, PID loops, drum sequences, shift registers, ramp generators, and more. When building a PLC ladder, users can incorporate function blocks that feature more complex instructions.

In addition to improving scan time, these blocks can replace entire physical components of your system, such as hard-wired mechanical timers. One example includes:. For example, a technician will have to press two buttons for a given machine to turn on. Do you want to power on a light switch? What about turn off a conveyor belt or enable a machine to pause every three minutes?

Next, list all the conditions that will play into your program. Using the light switch example, one condition would be that when you flip the switch upward, the light comes on. Then, when you flip it downward, the light turns off. Create a flowchart referencing these conditions for visual representation.

Your last step is to download the program to your PLC. When the transfer is done, you can disconnect your programming device. As industrial control systems continue to advance in terms of sophistication and function, PLCs will become even more multi-faceted and diverse. Want more information on industrial controls? Looking for top-of-the-line components that can help you build a future-focused system that delivers? We offer a wide range of control products in our online shop.

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