1769-IF8 CompactLogix 罗克韦尔8通道模拟电压/电流输入模块

1769-IF8 CompactLogix 罗克韦尔8通道模拟电压/电流输入模块

1769-IF8 CompactLogix 罗克韦尔8通道模拟电压/电流输入模块

(1）从控制方法上看

电器控制系统控制逻辑采用硬件接线，利用继电器机械触点的串联或井联等组合成控制逻辑，其连线多且复杂、体积大、功耗大，系统构成后，想再改变或增加功能较为困难。另外，继电器的触点数量有限，所以电器控制系统的灵活性和可扩展性受到很大限制。而PLC采用了计算机技术，其控制逻辑是以程序的方式存放在存储器中，要改变控制逻辑只需改变程序，因而很容易改变或增加系统功能。系统连线少、体积小、功耗小，而且PLC的“软继电器”实质上是存储器单元的状态，所以“软继电器”的触点数最是无限的，PLC系统的灵活性和可扩展性好。

（2）从工作方式上看

在继电器控制电路中。当电源接通时，电路中所有继电器都处于受制约状态，即该吸合的继电器都同时吸合。不该吸合的继电器受某种条件限制而不能吸合，这种工作方式称为并行工作方式。而PLC的用户程序是按一定顺序循环执行的，所以各软继电器都处于周期性循环扫描接通中，受同一条件制约的各个继电器的动作次序决定于程序扫描顺序，这种工作方式称为串行工作方式。

（3）从控制速度上看

继电器控制系统依靠机械触点的动作以实现控制，工作孩率低。机械触点还会出现抖动问题。而PLC通过程序指令控制半导体电路来实现控制，速度快，程序指令执行时间在微秒级，且不会出现触点抖动间题。

1769-IF8 CompactLogix 罗克韦尔8通道模拟电压/电流输入模块

(1) From the control method

The control logic of the electrical control system uses hardware wiring, and uses the series or well connection of the relay mechanical contacts to form a control logic, which has many and complex connections, large volume and large power consumption. After the system is formed, it is difficult to change or increase the function. In addition, the number of relay contacts is limited, so the flexibility and scalability of the electrical control system is greatly limited. The PLC uses computer technology, its control logic is stored in the memory in the way of a program, to change the control logic only need to change the program, so it is easy to change or increase the system function. The system connection is less, the size is small, the power consumption is small, and the PLC "soft relay" is essentially the state of the memory unit, so the "soft relay" contacts are the most unlimited, and the PLC system has good flexibility and scalability.

(2) From the way of work

In the relay control circuit. When the power supply is switched on, all relays in the circuit are in a restricted state, that is, the relays that are drawn are drawn at the same time. The relay that should not be drawn is limited by some conditions and cannot be drawn, and this working mode is called parallel working mode. The PLC user program is cyclic execution in a certain order, so the soft relays are in a periodic cycle of scanning on, subject to the same conditions of each relay action order determined by the program scanning order, this mode of work is called serial mode of work.

(3) From the control speed

The relay control system relies on the action of mechanical contacts to achieve control, and the working rate is low. Mechanical contacts will also have a shaking problem. The PLC controls the semiconductor circuit through the program instruction to achieve control, the speed is fast, the program instruction execution time is in the microsecond level, and there is no contact jitter problem.