Step 7 generate a 1s pulse

[larry]

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What's the best way to generate a 1s pulse in a PLC program? The first way is to use a clock memory with rising edge instructions, and the second way involves using logic instructions like AND, OR, and NOT to handle the clock memory. I'm using STEP7.

 

[Mrtain]

Maybe you can use a cyclic Interrupt OB to create the pulse Signals.

 

[PN/DP]

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What's the best way to generate a 1s pulse in a PLC program?

You mean a single pulse that starts at an event?

The easiest way is to use an S7 timer: S_PULSE (S_IMPULS) or S_PEXT (S_VIMP).
You can also create the pulse with S_ODT (S_EVERZ), but that requires a few more AND/OR operations. If you use S_OFFDT (S_AVERZ), the pulse will be 1 second + 1x the OB1 cycle time, or you can keep the timer active and let the trigger bit drop when the event occurs.

Another way: In OB1 you can add #OB1_PREV_CYCLE until >= 1000 (ms).

By the way: There's a CPU clock flag %Mx.7 that's exactly 1 second long and has a 1 second pause. Unfortunately, you can't control when the pulse starts. The same problem when using a cyclic OB.

 

[larry]

You mean a single pulse that starts at an event?

The easiest way is to use an S7 timer: S_PULSE (S_IMPULS) or S_PEXT (S_VIMP).
You can also create the pulse with S_ODT (S_EVERZ), but that requires a few more AND/OR operations. If you use S_OFFDT (S_AVERZ), the pulse will be 1 second + 1x the OB1 cycle time, or you can keep the timer active and let the trigger bit drop when the event occurs.

Another way: In OB1 you can add #OB1_PREV_CYCLE until >= 1000 (ms).

By the way: There's a CPU clock flag %Mx.7 that's exactly 1 second long and has a 1 second pause. Unfortunately, you can't control when the pulse starts. The same problem when using a cyclic OB.

In the PLC program, we often use the method from 1.png to generate 1-second pulses, while the method in 2.png is only used in OB35.

What are the advantages of using the method in 1.png?

 

[larry]

You mean a single pulse that starts at an event?

The easiest way is to use an S7 timer: S_PULSE (S_IMPULS) or S_PEXT (S_VIMP).
You can also create the pulse with S_ODT (S_EVERZ), but that requires a few more AND/OR operations. If you use S_OFFDT (S_AVERZ), the pulse will be 1 second + 1x the OB1 cycle time, or you can keep the timer active and let the trigger bit drop when the event occurs.

Another way: In OB1 you can add #OB1_PREV_CYCLE until >= 1000 (ms).

By the way: There's a CPU clock flag %Mx.7 that's exactly 1 second long and has a 1 second pause. Unfortunately, you can't control when the pulse starts. The same problem when using a cyclic OB.

2.png is incorrect, new_2.png is correct.

 

[PN/DP]

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You mean a single pulse that starts at an event?

You didn't answer my question. What do you need the pulse for? Or a cyclical clock?

The clock bits of the CPU clock memory byte are asynchronous to events from the process and asynchronous to OB1.
The clock bits can simply be used as a flashing clock for lamps or to count seconds, but not for a pulse that must start when an event occurs.

 

[PN/DP]

The clock bits can simply be used as a flashing clock for lamps or to count seconds, but not for a pulse that must start when an event occurs.

Example:

                 +---+     #out
"clockbit_1Hz" --| & |     +---+
    "condition"--|   |-----| = |
                 +---+     +---+

If the condition becomes true then #out will be
- either true immediately, but for less than 0.5s
- or true up to 0.5s later, but then for exactly 0.5s

---> #out is not synchronous with the condition

 

[larry]

你没有回答我的问题。您需要 pulse 做什么？还是一个周期性的时钟？

CPU clock memory 字节的 clock bits 与来自进程的事件异步，并与 OB1 异步。
clock bits 可以简单地用作 lamps 的闪烁时钟或计算秒数，但不能用于事件发生时必须启动的脉冲。

Generate a continuous 1-second pulse without interruption. For example, when the fault wait time for the valve adds up to 3 seconds, a failure alarm is triggered.
However, in the PLC project, the clock memory byte is completed with logical instructions (e.g., XOR and AND) to generate a 1s pulse.