One Shot Rising & one Shot Falling Instructions in PLC

One Shot Rising Instructions in PLC Programming

Programmable Logic Controllers (PLCs) have revolutionized the automation industry by providing a reliable and efficient way to control industrial processes. PLCs use various programming techniques to execute complex logic and decision-making tasks. One such technique is the use of One-Shot Rising (OSR) in ladder logic programming.

OSR is a logical element used in ladder logic programming that detects a rising edge of a signal or input. A rising edge is a transition from a low or zero state to a high or one state. OSR functions as a memory element and holds the output high for one scan cycle when the input signal rises. After one scan cycle, the output returns to its low state, regardless of the input signal status.

OSR is useful in applications where it is necessary to ensure that an event occurs only once. For example, in a machine control system, it may be necessary to ensure that a specific sequence of operations is carried out only once. OSR can be used to detect the beginning of the sequence and hold the output high until the sequence is completed. Once the sequence is completed, the output returns to its low state.

Another application of OSR is in pulse generation. In this application, a pulse is generated when an input signal rises. The pulse width is determined by the scan time of the PLC. For example, if the scan time of the PLC is 10 milliseconds, then the pulse width will be 10 milliseconds. This functionality can be used to control the speed of a motor or to generate a signal to trigger a camera.

OSR also reduces the need for complex programming techniques such as timers and counters. Timers and counters are used to perform repetitive tasks or to generate time delays. However, they can be complex to program and can consume valuable memory resources. OSR simplifies programming and reduces memory usage by performing the same task in a single line of code.

To understand the functionality of OSR, consider the following example. Assume that a machine control system requires that a specific sequence of operations is carried out only once. The sequence involves turning on a motor, waiting for 5 seconds, and then turning off the motor. The sequence should be initiated by pressing a start button.

To achieve this functionality using OSR, the following ladder logic program can be used:

|—-[Start]—-| OSR |—–[M1]—–|

|————–[5 sec]————–|

In this program, the start button is connected to the input of the OSR element. When the start button is pressed, the input signal rises, and the OSR element detects the rising edge. The output of the OSR element is held high for one scan cycle, which activates the motor (M1). The timer element is used to generate a delay of 5 seconds. After 5 seconds, the timer output rises, which turns off the motor (M1). The output of the OSR element returns to its low state, ensuring that the sequence is carried out only once.

In simple, One-Shot Rising is a powerful programming technique used in ladder logic programming for PLCs. It is a simple and efficient way to detect rising edges of input signals, generate pulses, and simplify programming. Its applications range from simple pulse generation to complex machine control systems. Understanding the functionality and benefits of OSR is essential for programmers and engineers working with PLCs. By using OSR, programmers can simplify programming, reduce memory usage, and achieve complex control tasks with ease.

One Shot Falling Instructions in PLC Programming

Programmable Logic Controllers (PLCs) are widely used in industrial automation to control and monitor machines and processes. PLCs use ladder logic programming to create control programs that execute logic and decision-making tasks. One common programming technique used in PLCs is the One-Shot Falling (OSF) instruction. In this article, we will explore the functionality and applications of the OSF instruction.

One-Shot Falling (OSF) Instruction

The OSF instruction in ladder logic programming is a logical element that detects a falling edge of an input signal. A falling edge is a transition from a high or one state to a low or zero state. The OSF instruction functions as a memory element and holds the output low for one scan cycle when the input signal falls. After one scan cycle, the output returns to its high state, regardless of the input signal status.

The OSF instruction is useful in applications where it is necessary to ensure that an event occurs only once. For example, in a machine control system, it may be necessary to ensure that a specific sequence of operations is carried out only once. OSF can be used to detect the end of the sequence and hold the output low until the sequence is completed. Once the sequence is completed, the output returns to its high state.

Another application of OSF is in pulse generation. In this application, a pulse is generated when an input signal falls. The pulse width is determined by the scan time of the PLC. For example, if the scan time of the PLC is 10 milliseconds, then the pulse width will be 10 milliseconds. This functionality can be used to control the speed of a motor or to generate a signal to trigger a camera.

The OSF instruction can also be used in conjunction with the OSR instruction to create more complex control tasks. For example, the OSR instruction can be used to detect the rising edge of an input signal to start a process, and the OSF instruction can be used to detect the falling edge of the same signal to stop the process.

OSF Instruction in Ladder Logic Programming

To use the OSF instruction in ladder logic programming, it is necessary to understand its syntax and functionality. The syntax of the OSF instruction is similar to the OSR instruction:

OSF|—-[Input]—-|—-[Output]—-|

In this syntax, the vertical bars indicate the OSF instruction, the input signal, and the output signal. When the input signal falls, the output signal is held low for one scan cycle. After one scan cycle, the output signal returns to its high state.

To understand the functionality of the OSF instruction, consider the following example. Assume that a machine control system requires that a specific sequence of operations is carried out only once. The sequence involves turning on a motor, waiting for 5 seconds, and then turning off the motor. The sequence should be initiated by pressing a start button and stopped by pressing a stop button.

To achieve this functionality using OSF, the following ladder logic program can be used:

|—-[Start]—-| OSR |—–[M1]—–|

|————–[5 sec]————–|

|—-[Stop]—–| OSF |—–[M1]—–|

In this program, the start button is connected to the input of the OSR instruction. When the start button is pressed, the input signal rises, and the OSR instruction detects the rising edge. The output of the OSR instruction is held high for one scan cycle, which activates the motor (M1). The timer element is used to generate a delay of 5 seconds. After 5 seconds, the timer output rises, which turns off the motor.

The stop button is connected to the input of the OSF instruction. When the stop button is pressed, the input signal falls, and the OSF instruction detects the falling edge. The output of the OSF instruction is held low for one scan cycle, which deactivates the motor (M1). This ensures that the motor is turned off only once, even if the stop button is held down for a longer time.

Conclusion

The One-Shot Falling (OSF) instruction in PLC programming is a useful logical element that detects a falling edge of an input signal. It functions as a memory element and holds the output low for one scan cycle when the input signal falls. The OSF instruction is useful in applications where it is necessary to ensure that an event occurs only once or to generate a pulse of a specific width. The OSF instruction can be used in conjunction with other logical elements, such as the OSR instruction, to create more complex control tasks. Understanding the syntax and functionality of the OSF instruction is crucial for PLC programmers to create efficient and effective control programs for industrial automation.

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