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Programmable logic controllers (PLCs) are small computing devices used in factories to operate machinery. Programmers alter processes on PLCs to make changes to the product being manufactured. Tips for programmers include using a single operation, implementing a proportional controller, creating switching logic, and reducing PLC scan time issues. Absolute position encoders are recommended over incremental encoders for high-speed machines.
Programmable logic controllers are small computing devices used in factories and industry to operate machinery. Having their own operating systems, programmable logic controllers (PLCs) control the processes used to manufacture products. Programmers alter processes on PLCs to operate machinery and make changes to the product being manufactured. They use programmable logic controller programming in areas such as processing, food packaging, and material handling. Some of the best tips for programmers are using a single operation, implementing a proportional controller in your logic, creating switching logic, and reducing PLC scan time issues.
The one shot function is useful when a condition turns on and off and the PLC needs to act on the real state for only one scan. The coil goes true whenever the enabling loop is true and stays true for only one scan. Sometimes, the order of the rungs becomes important in one fell swoop because the PLC has to complete a full scan when the output bit is on and only then does it see the first rung.
Integrating proportional controllers into a PLC becomes very useful in programming programmable logic controllers, especially when it does not have built-in proportional/integral/derived or PID instructions. PID controllers are process controllers with special tunable response characteristics. This allows them to successfully execute control algorithms that anticipate and measure the heating and cooling rates of the process and self-correct. Process control procedures use proportional controllers in a myriad of ways; having total control over your heating is a popular application. PLCs can be precisely programmed to turn the heater on or to turn it on and off.
A popular method in programmable logic controller programming uses the concept of switching. This logic is useful when the programmer needs to have a push button control a device with the same switching action. For example, pressing a button once turns the device on and pressing it again turns it off. This logic transitions from the off state to the on state when the input becomes true. Then it stays active until the input becomes false.
Long PLC scan times can also be a problem in programmable logic controller programming, especially when designing controls for high-speed machines. A popular approach uses incremental coding to calculate the location of the car. This approach, however, can cause a lot of problems when trying to make the machine run faster. If the output of the encoder working at the increased speed goes from false to true and goes back in time for the PLC to perform one scan, the counter is not counting correctly. This causes the machine to stop or go out of sync with moving parts when speed is increased.
The solution in such a scenario is to use an absolute position encoder instead of an incremental encoder. The advantage of this type of encoder is that it is less prone to errors as the speed of the machine increases. This encoder, however, requires about a dozen or more input lines compared to the two lines an incremental encoder needs. Absolute encoders can also produce errors such as missing states, where some bits change and some don’t. If you experience skipped states with an absolute encoder, you must replace it with another one.
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