使用PLC的自动化制造系统——3.2输入和输出

3.2 INPUTS AND OUTPUTS

3.2输入和输出

Inputs to, and outputs from, a PLC are necessary to monitor and control a process. Both inputs and outputs can be categorized into two basic types: logical or continuous. Consider the example of a light bulb. If it can only be turned on or off, it is logical control. If the light can be dimmed to different levels, it is continuous. Continuous values seem more intuitive, but logical values are preferred because they allow more certainty, and simplify control. As a result most controls applications (and PLCs) use logical inputs and outputs for most applications. Hence, we will discuss logical I/O and leave continuous I/O for later.

输入到和输出到，是PLC是必要的监测和控制的过程。 输入和输出都可以分为两种类型：逻辑的或连续的。 看一个点亮灯泡的例子。如果它只能打开或关闭，这是逻辑的控制。 如果光线可以变暗到不同层次，它是连续的。连续的值观似乎更直观的，但逻辑值是首选的，因为它们允许更多的确定性和简化的控制。因此，大多数控制的应用程序对于大多数应用场合（包括PLC）使用逻辑输入和输出。因此，我们将讨论逻辑I/O，连续的I/O随后讨论。

Outputs to actuators allow a PLC to cause something to happen in a process. A short list of popular actuators is given below in order of relative popularity.

Solenoid Valves - logical outputs that can switch a hydraulic or pneumatic flow.

Lights - logical outputs that can often be powered directly from PLC output boards.

Motor Starters - motors often draw a large amount of current when started, so they require motor starters, which are basically large relays.

Servo Motors - a continuous output from the PLC can command a variable speed or position.

在控制过程中，输出对执行器允许PLC使一些事情发生。常用的执行器名单以相对受欢迎程度列出如下：

电磁阀-逻辑输出，可以切换液压或气流。

灯-逻辑输出，通常可以直接从PLC输出点亮。

电动机起动器-电机起动时常常引起较大的电流，因此需要电动机起动器，基本上是大的继电器。

伺服电机-从PLC的连续输出可以控制一个可变的速度或位置。

Outputs from PLCs are often relays, but they can also be solid state electronics such as transistors for DC outputs or Triacs for AC outputs. Continuous outputs require special output cards with digital to analog converters.

PLC的输出常常是继电器，但它们也可以是固体电子产品，例如直流输出或双向交流输出的晶体管。连续输出要求特别的数字量到模拟量转换输出卡。

Inputs come from sensors that translate physical phenomena into electrical signals. Typical examples of sensors are listed below in relative order of popularity.

来自传感器的输入要将物理信号转换为电信号。 下面列出的是按相对常用顺序的传感器典型的例子。

Proximity Switches - use inductance, capacitance or light to detect an object logically.

Switches - mechanical mechanisms will open or close electrical contacts for a logical signal.

Potentiometer - measures angular positions continuously, using resistance.

LVDT (linear variable differential transformer) - measures linear displacement continuously using magnetic coupling.

接近开关-使用电感，电容或光在逻辑上检测对象。

开关-机械装置，将打开或关闭电气触点得到一个逻辑上的信号。

电位器-利用阻抗连续测量角度、位置。

 LVDT（线性可变差动变压器） -利用磁耦合测量连续的线性位移。

Inputs for a PLC come in a few basic varieties, the simplest are AC and DC inputs. Sourcing and sinking inputs are also popular. This output method dictates that a device does not supply any power. Instead, the device only switches current on or off, like a simple switch.

最初PLC的输入有几个基本的类型，最简单的是交流和直流输入。 源和漏输入也很常用。这种输出方法要求设备不提供电源。相反，设备只能接通或关断电流，像一个简单的开关。

Sinking - When active the output allows current to flow to a common ground. This is best selected when different voltages are supplied.

Sourcing - When active, current flows from a supply, through the output device and to ground. This method is best used when all devices use a single supply voltage.

漏-输出激活时允许电流流向一个共同地。当不同的电压供电时，这个是最好的选择。

源-当激活时，电流从电源端通过输出设备和地。此方法最适合用于所有设备都使用单电源电压。

This is also referred to as NPN (sinking) and PNP (sourcing). PNP is more popular. This will be covered in detail in the chapter on sensors.

这也被称为NPN型（漏型）和PNP型（源型）。PNP型更常见。详细的会在传感器的一章描述。