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plc中常用指令(plc常用指令表)

Master Controls / 主控指令

Let's now look at what are called master controls. Master controls can be thought of as "emergency stop switches". An emergency stop switch typically is a big red button on a machine that will shut it off in cases of emergency. Next time you're at the local gas station look near the door on the outside to see an example of an e-stop. **IMPORTANT – We're not implying that this instruction is a substitute for a "hard wired" e-stop switch. There is no substitute for such a switch! Rather it's just an easy way to get to understand them.

现在让我们看看所谓的主控指令。主控指令可以被认为是“紧急停止开关”。紧急停止开关通常是机器上一个红色的大按钮,在紧急情况下可以关闭它。下次你在当地加油站的时候,看看外面的门,看看紧急停止按钮e-stop的例子(国内加油站好像没有吧^_^)。

** 重要 – 我们并不是在暗示这个主控指令是“硬连线”e-stop开关的替代品。这个主控指令的功能仅仅靠这样一个开关是无法替代的!相反,这种比喻只是一种理解它们的简单方法。

The master control instruction typically is used in pairs with a master control reset. However this varies by manufacturer. Some use MCR in pairs instead of teaming it with another symbol. It is commonly abbreviated as MC/MCR (master control/master control reset), MCS/MCR (master control set/master control reset) or just simply MCR (master control reset).

主控指令通常与主控复位指令成对使用。然而,这取决于不同品牌的PLC,有些PLC成对使用MCR,而不是与另一个符号MC组合。它通常缩写为MC / MCR (master control/master control reset)、 MCS / MCR (master control set/master control reset)、或者只有简单的MCR (master control reset)。

plc中常用指令(plc常用指令表)

Here is one example of how a master control symbol looks / 这是主控指令的符号

plc中常用指令(plc常用指令表)

Below is an example of a master control reset / 这是主控复位指令的符号

To make things interesting, many manufacturers make them act differently. Let's now take a look at how it's used in a ladder diagram. Consider the following example:

更有趣的是,不同的制造商生产的PLC其主控指令工作方式略有不同。现在让我们看看它是如何在梯形图中使用的。参考下面的例子:

plc中常用指令(plc常用指令表)

Here's how different PLCs will run this program:

下面讲解的是不同品牌的PLC运行这个程序的情况:

Manufacturer X – In this example, rungs 2 and 3 are only executed when input 0000 is on (true). If input 0000 is not true the plc pretends that the logic between the mc and mcr instructions does not exist. It would therefore bypass this block of instructions and immediately go to the rung after the mcr instruction.

制造商X – 在本例中,梯形图中横档Rung 2和Rung 3只有在输入0000为“真”(True)时才会被执行(即被扫描),如果输入0000为“假”(False),则PLC假装主控指令MC和主控复位指令MCR之间的逻辑不存在(即不被扫描),因此,PLC会绕过Rung 2和Rung 3这两个横档的指令块,立即执行MCR指令之后的其他程序。

Conversely, if input 0000 is true, the plc would execute rungs 2 and 3 and update the status of outputs 0500 and 0501 accordingly. So, if input 0000 is true, program execution goes to rung 2. If input 0001 is true 0500 will be true and hence it will turn on when the plc updates the outputs. If input 0002 is true (i.e. physically off) 0501 will be true and therefore it will turn on when the plc updates the outputs.

相反,如果输入0000为“真”(True),PLC将执行横档Rung 2和Rung 3,并相应地更新输出0500和0501的状态。因此,如果输入0000为“真”(True),程序执行进入第Rung 2档,如果输入0001为“真”(True),则输出0500为“真”(True),因此当plc更新输出时,输出0500将被打开;如果常闭触点0002为“真”(True),则输出0501为“真”(True),因此当plc更新输出时,输出0501将被打开。

MCR just tells the plc "that's the end of the mc/mcr block".

主控复位指令MCR只是告诉PLC“到这里MC/MCR指令结束了”。

In this plc, scan time is not extended when the mc/mcr block is not executed because the plc pretends the logic in the block doesn't exist. In other words, the instructions inside the block aren't seen by the plc and therefore it doesn't execute them.

在这个品牌的PLC中,当MC/MCR指令不执行时,扫描时间不会延长,因为PLC假装MC/MCR指令之间的逻辑程序都不存在,换句话说,PLC看不到MC/MCR指令之间的逻辑程序,因此不会执行它们(即不扫描它们也就节省了扫描时间)。

plc中常用指令(plc常用指令表)

In the example above, we can see the effects of the MC/MCR on an OutB (outbar) instruction. Remember that if the MC/MCR block were not there 0500 would be physically on only when input 0001 was false (physically off). But since the MC/MCR block is there, this happens only when input 0000 is true. When input 0000 is false it is impossible for 0500 above to be on.

在上面的例子中,我们可以看到MC/MCR指令对OutB(OutB 0500)指令的影响。请记住,如果程序中没有MC/MCR指令,那么只有在输入0001为“假”(False即物理上为OFF)时, 输出0500才会有物理意义上的ON状态;但是因为程序中有MC/MCR指令,所以只有输入0000为“真”(True)时才会发生这种情况。当输入0000为“假”(False)时,梯形图中的0500永远不可能打开。

Manufacturer Y – In this example, rungs 2 and 3 are always executed regardless of the status of input 0000. If input 0000 is not true the plc executes the MC instruction. (i.e. MC becomes true) It then forces all the input instructions inside the block to be off. If input 0000 is true the MC instruction is made to be false.

制造商Y – 在本例中,无论输入0000的状态如何,梯形图中横档Rung 2和Rung 3都会被执行,只不过与制造商X不同,如果输入0000为“假”(False),PLC会执行MC指令(即MC变为“真”),然后PLC会强制MC/MCR指令之间的所有横档上的所有输入指令关闭(即变为“假”);如果输入0000为“真”(True),则PLC不会执行MC指令(即MC变为“假”)。

Then, if input 0000 is true, program execution goes to rung 2. If input 0001 is true 0500 will be true and hence it will turn on when the plc updates the outputs. If input 0002 is true (i.e. physically off) 0501 will be true and therefore it will turn on when the plc updates the outputs. MCR just tells the plc "that's the end of the mc/mcr block". When input 0000 is false, inputs 0001 and 0002 are forced off regardless if they're physically on or off. Therefore, outputs 0500 and 0501 will be false.

然后,如果输入0000为“真”(True),MC指令变为“假”(False),程序执行进入梯形图中横档Rung 2和Rung 3,如果输入0001为“真”(True),则输出0500为“真”,因此当PLC更新输出状态时,输出0500将被打开。如果输入常闭触点0002为“真”(True),则输出0501为“真”,因此当PLC更新输出状态时,输出0501将被打开,MCR指令只是告诉PLC“这是MC/MCR指令的结束”;当输入0000为“假”(False)时,无论输入0001和0002在物理意义上是开还是关,它们都会被强制关闭(即变为“假”),因此,输出0500和0501只能为“假”(False)。

The difference between manufacturers X and Y above is that in the Y scheme the scan time will be the same (well close to the same) regardless if the block is on or off. This is because the plc sees each instruction whether the block is on or off.

上面的两个制造商X和Y之间的区别在于,在Y方案中,无论MC指令是“真”还是“假”,扫描时间都是相同的(或者非常接近),这是因为无论MC指令是“真”还是“假”,PLC都会扫描到每条指令。

Most all manufacturers will make a previously latched instruction (one that's inside the mc/mcr block) retain its previous condition.

大多数制造商会使用前面讲到的锁存指令(位于MC/MCR块的内部)保持其先前的状态。

If it was true before, it will remain true. / 如果以前是“真”(True),现在也还是“真”(True)。

If it was false before, it will remain false. / 如果以前是“假”(False),现在也还是“假”(False)。

Timers should not be used inside the mc/mcr block because some manufacturers will reset them to zero when the block is false whereas other manufacturers will have them retain the current time state.

计时器不应该在MC/MCR指令之间的程序中使用,因为当MC指令为“假”(False)时,有的制造商会将计时器重置为零,而有的制造商会让计时器保持当前的时间状态。

Counters typically retain their current counted value.

计数器通常保持它们当前计数的值。

Here's the part to note most of all. When the mc/mcr block is off, (i.e. input 0000 would be false in the ladder example shown previously) an OUTB (OutBar or OutNot) instruction would not be physically on. It is forced physically off.

这里是最值得注意的部分。当MC/MCR指令关闭时(例如,在前面显示的梯形图示例中,输入0000是“假”时),OutB (OutBar或OutNot)指令将不会在物理上打开,它是物理上强制关闭的。

plc中常用指令(plc常用指令表)

OutBar instruction / OutBar指令

BE CAREFUL! Most manufacturers use the manufacturer Y execution scheme shown above. When in doubt, however, read the manufacturers instruction manual. Better yet, just ask them.

注意注意!大多数制造商使用上面所讲的制造商Y执行方案。如果有疑问,请阅读制造商的说明书。更好的办法是,直接问他们。

关于作者: tangshenmengchon

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