ABBPM825当PLC控制器投入运行后，其工作过程一般分为三个阶段，即输入采样、用户程序执行和输出刷新三个阶段。完成上述三个阶段称作一个扫描周期。在整个运行期间，PLC控制器的CPU以一定的扫描速度重复执行上述三个阶段。在输入采样阶段，PLC控制器以扫描方式依次地读入所有输入状态和数据，并将它们存入I/O映象区中的相应得单元内。输入采样结束后，转入用户程序执行和输出刷新阶段。在这两个阶段中，即使输入状态和数据发生变化，I/O映象区中的相应单元的状态和数据也不会改变。因此，如果输入是脉冲信号，则该脉冲信号的宽度必须大于一个扫描周期，才能保证在任何情况下，该输入均能被读入。
PM825
PM825数字量输入输出信号就是开关量信号，1或者0， 模拟量信号，有2种，电压或者电流信号 ，一般是变送器传过来的信号，比如用压力变送器检测水管压力，它会输出一个模拟信号4–20ma 或者 0-10V的信号给PLC，PLC来进行数据处理。 开关量输入点(DI),处理开关量输入信号. 模拟量输入点(AI),处理模拟量输入信号(0-20mADC,0-5VDC). 电阻信号(含热电阻)输入点,处理热电阻或一般电阻信号. 高速脉冲输入点,处理高速脉冲信号. 电压(含热电偶)输入点,处理电压输入或热电偶信号. 还有通讯,用于和上位机交换数据或控制下级控制器仪表驱动器等 。
PM825
在用户程序执行阶段，PLC控制器总是按由上而下的顺序依次地扫描用户程序(梯形图)。在扫描每一条梯形图时，又总是先扫描梯形图左边的由各触点构成的控制线路，并按先左后右、先上后下的顺序对由触点构成的控制线路进行逻辑运算，然后根据逻辑运算的结果，刷新该逻辑线圈在系统RAM存储区中对应位的状态;或者刷新该输出线圈在I/O映象区中对应位的状态;或者确定是否要执行该梯形图所规定的特殊功能指令。
PM825
After the ABBPM825 PLC controller is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution, and output refresh. Completing the above three stages is called a scanning cycle. During the entire operation period, the CPU of the PLC controller repeatedly executes the above three stages at a certain scanning speed. In the input sampling stage, the PLC controller sequentially reads in all input states and data in a scanning manner, and stores them in the corresponding units in the I/O image area. After the input sampling is completed, it enters the user program execution and output refresh phase. In these two stages, even if the input state and data change, the state and data of the corresponding units in the I/O image area will not change. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scanning cycle to ensure that the input can be read in any case.
PM825
The PM825 digital input and output signal is a switch signal, 1 or 0, analog signal, which has two types: voltage or current signal. Generally, it is a signal transmitted by the transmitter. For example, if a pressure transmitter is used to detect water pipe pressure, it will output an analog signal of 4-20mA or 0-10V to the PLC for data processing. Switching input point (DI), processing switching input signals Analog input point (AI), processing analog input signals (0-20mADC, 0-5VDC) Resistance signal (including thermal resistance) input point, processing thermal resistance or general resistance signals High speed pulse input point, processing high-speed pulse signals Voltage (including thermocouple) input point, processing voltage input or thermocouple signal There is also communication used to exchange data with the upper computer or control the instrument drivers of the lower controller.
PM825
During the user program execution phase, the PLC controller always scans the user program (ladder diagram) in a top-down order. When scanning each ladder diagram, always scan the control circuit composed of each contact on the left side of the ladder diagram first, and perform logical operations on the control circuit composed of the contacts in the order of left to right, top to bottom. Then, based on the results of the logical operations, refresh the corresponding bit status of the logical coil in the system RAM storage area; Or refresh the state of the corresponding bit of the output coil in the I/O image area; Or determine whether to execute the special functional instructions specified in the ladder diagram.
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