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PLC基本知识--6.4晶体管输出(顺便学英文)

PLC基本知识--6.4晶体管输出(顺便学英文)

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PLC基本知识--6.4晶体管输出(顺便学英文)

Transistor Outputs / 晶体管输出

The next type of output we should learn about is our transistor type outputs. It is important to note that a transistor can only switch a dc current. For this reason it cannot be used with an AC voltage.

我们应该了解的下一种输出类型是晶体管类型的输出。重要的是要注意,晶体管只能用于直流电流,由于这个原因,它不能用于交流电压。

We can think of a transistor as a solid-state switch. Or more simply put, an electrical switch. A small current applied to the transistors base (i.e. input) lets us switch a much larger current through its output. The plc applies a small current to the transistor base and the transistor output closes. When its closed, the device connected to the plc output will be turned on. The above is a very simple explanation of a transistor. There are, of course, more details involved but we dont need to get too deep.

我们可以把晶体管想象成一个固态开关,或者更简单地说,是一个电气开关。施加在晶体管“基极”(即输入端)上的很小的电流使我们可以通过晶体管的输出来控制大得多的电流。PLC对晶体管基极施加小电流,晶体管输出“闭合”,当它闭合时,连接到PLC输出端的设备将被接通。以上是对晶体管输出的一个非常简单的解释,当然,还有关于晶体管功能更多的细节,在这里我们不需要太深入。

We should also keep in mind that as we saw before with the input circuits, there are generally more than one type of transistor available. Typically a plc will have either NPN or PNP type outputs.The physical type of transistor used also varies from manufacturer to manufacturer. Some of the common types available are BJT and MOSFET. A BJT type (Bipolar Junction Transistor) often has less switching capacity (i.e. it can switch less current) than a MOS-FET (Metal Oxide Semiconductor- Field Effect Transistor) type. The BJT also has a slightly faster switching time. Once again, please check the output specifications of the particular plc you are going to use. Never exceed the manufacturers maximum switching current.

我们还应该记住,正如我们之前看到的输入电路,通常有多种的晶体管可用。通常,PLC会有NPN或PNP类型的输出,使用的“物理”型晶体管也因制造商不同而各异,一些常见的类型是BJT和MOSFET,BJT型(双极结晶体管)通常比MOS-FET型(金属氧化物半导体-场效应晶体管)具有更小的开关容量(即它可以切换更少的电流)。BJT的切换时间也稍快一些。请再次检查您将要使用的特定PLC的输出规格。永远不要超过制造商的最大开关电流。

PLC基本知识--6.4晶体管输出(顺便学英文)_WWW.XUNWANGBA.COM

Shown above is how we typically connect our output device to the transistor output. Please note that this is an NPN type transistor. If it were a PNP type, the common terminal would most likely be connected to V+ and V- would connect to one end of our load. Note that since this is a DC type output we must always observe proper polarity for the output. One end of the load is connected directly to V+ as shown above.

上图显示的是通常情况下我们如何连接我们的负载到晶体管输出型的PLC输出端,请注意图中画的是一个NPN型晶体管。如果它是一种PNP类型,那么PLC公共端很可能连接到电源正极V+,而电源负极V-则连接到负载的一端。注意,由于这是一个直流类型的输出,我们必须始终要注意输出的极性是否正确。上图所示的负载的一端是直接连接到电源正极V+的。

Lets take a moment and see what happens inside the output circuit. Shown below is a typical output circuit diagram for an NPN type output.

让我们花点时间看看在输出电路里发生了什么。下图是NPN类型输出的典型输出电路图。

PLC基本知识--6.4晶体管输出(顺便学英文)_WWW.XUNWANGBA.COM

Notice that as we saw with the transistor type inputs, there is a photocoupler isolating the real world from the internal circuit. When the ladder diagram calls for it, the internal circuit turns on the photocoupler by applying a small voltage to the LED side of the photocoupler. This makes the LED emit light and the receiving part of the photocoupler will see it and allow current to flow. This small current will turn on the base of the output transistor connected to output 0500. Therefore, whatever is connected between COM and 0500 will turn on. When the ladder tells 0500 to turn off, the LED will stop emitting light and hence the output transistor connected between 0500 and COM will turn off.

注意,正如我们看到的晶体管类型的输入,在晶体管输出回路中有一个光电耦合器用来从内部电路隔离“现实世界”。当梯形图需要输出时,内部电路通过在光耦合器的LED一侧施加一个小电压来接通光耦合器,这使得LED发光,光电耦合器的接收部分将看到它,并允许接收部分内部电流开始流动,这个小电流将接通输出晶体管的基极使其连接到PLC输出点0500。因此,COM和0500之间的任何负载都会被接通。当梯形图需要输出点0500断开时,LED将停止发光,因此连接在0500和COM之间的输出晶体管将断开,输出回路上的负载也就断开了。

One other important thing to note is that a transistor typically cannot switch as large a load as a relay. Check the manufacturers specifications to find the largest load it can safely switch. If the load current you need to switch exceeds the specification of the output, you can connect the plc output to an external relay. Then connect the relay to the large load. You may be thinking, why not just use a relay in the first place? The answer is because a relay is not always the correct choice for every output. A transistor gives you the opportunity to use external relays when and only when necessary.

另一件需要注意的重要事情是晶体管通常不能像继电器那样有大的负载。检查制造商的产品规格,搞清楚晶体管输出回路能承载的最大安全负载。如果你需要控制的负载电流超过了输出的规格,你可以把PLC的输出先连接到一个外部继电器上,然后再将较大的负载连接到继电器上。你可能会想,“为什么不直接选择继电器输出类型的PLC呢?”答案是,对于每个输出,继电器输出并不一定是正确的选择。晶体管使你有机会在必要时和仅在必要时添加使用外部继电器。

In summary, a transistor is fast, switches a small current, has a long lifetime and works with dc only. Whereas a relay is slow, can switch a large current, has a shorter lifetime and works with ac or dc. Select the appropriate one based upon your actual application needs.

总而言之,晶体管速度快,开关电流小,寿命长,只适用于直流电。而继电器是缓慢的,可以切换大电流,有较短的寿命,可以在交流或直流下工作。根据您的实际应用程序需求选择适当的一个。

PLC基本知识--6.4晶体管输出(顺便学英文)_WWW.XUNWANGBA.COM

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