Allen-Bradley 1771-NIV PLC-5 8P 模拟电压/电流输入

　　在研发这款大型机械时，Agrometer主要与系统集成商Pagaard合作。双方进行了大量产品的选择及测试后，最终选择了ifm新型移动控制器、分布式I/O模块及传感器，实现简化机器的接线和维护，更快完成设置。

　　Pagaard的董事总经理兼共同所有人Torben Lund在解释为何决定使用ifm产品时说道：“最初，Agrometer使用的是工业级PLC。但很快我们发现工业级产品在移动机械上使用时存在耐用性问题，因为它们并非针对这类应用而设计的。因此我们在市场上寻找能承受移动应用严苛要求的技术。我们发现之前采购ifm的传感器，他们可提供一种我们认为非常适合该项任务的控制器。”

硬核控制器

　　Agrometer采用了ifm ecomatController控制器CR721S，其内部包含2个PLC单元，其中1个通过了相关认证，适用于安全等级高达EN 13849 PL d和EN 62061 SIL cl2的安全相关应用。双PLC配置的优势：2个内部独立的可编程控制器允许在必要时对应用软件进行进一步划分。因此，安全程序与一般程序可以相互无干扰地执行。强大的32位多核处理器即使在面对复杂的控制任务时也可确保快速执行程序。

　　Gate-level Logic Simulation

　　In an ideal logic simulation, the output changes instantaneously with any change on the inputs. In a real system, there is a “propagation delay” as the input voltage change propagates through the transistors in the circuit to cause a change in the output voltage. The output loads and the rise and fall times of the input and output signals also affect the total circuit signal propagation characteristics.

　　Timing Diagrams

　　Let’s look at the simple example of an inverter timing diagram as shown below in Figure 7. As the input, x, changes logic state, the output changes after a delay.

　　In this example, the falling output propagation delay, df, is shorter and has a steeper slope than the rising output delay, dr. The delays are measured at the 50% level between the two logic levels. This type of asymmetric response would occur in a CMOS inverter in which the NMOS and PMOS transistors were the same size. The higher drive current of the NMOS transistor would pull the output down more quickly than the PMOS transistor could pull the output up.