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plc的算法

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发表于 2012-6-11 17:51:51 | 显示全部楼层 |阅读模式
PLC中无非就是三大量:开关量、模拟量、脉冲量。只在搞清楚三者之间的关系,你就能熟练的掌握PLC了。 1 y1 d, _- t9 E& J) Y% X
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1、 开关量也称逻辑量,指仅有两个取值,0或1、ON或OFF。它是最常用的控制,对它进行控制是PLC的上风,也是PLC最基本的应用。
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7 w1 M7 P0 c3 F# l; q. [关量控制的目的是,根据开关量确当前输入组合与历史的输入顺序,使PLC产生相应的开关量输出,以使系统能按一定的顺序工作。所以,有时也称其为顺序控制。
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而顺序控制又分为手动、半自动或自动。而采用的控制原则有分散、集中与混合控制三种。 ( g! H9 B% Y# @4 H* U

3 {% D7 @2 o# j" Y4 r; l, x这是用OMRON的开关量编写的一个“单按钮启停”程序。
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+ w7 w, h2 d! |2、 模拟量是指一些连续变化的物理量,如电压、电流、压力、速度、流量等。
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PLC是由继电控制引入微处理技术后发展而来的,可方便及可靠地用于开关量控制。由于模拟量可转换成数字量,数字量只是多位的开关量,故经转换后的模拟量,PLC也完全可以可靠的进行处理控制。 2 a* `! D! j$ s3 ]( L- {* @/ s
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由于连续的生产过程常有模拟量,所以模拟量控制有时也称过程控制。
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* g& X/ O; g9 S模拟量多是非电量,而PLC只能处理数字量、电量。所有要实现它们之间的转换要有传感器,把模拟量转换成数电量。假如这一电量不是标准的,还要经过变送器,把非标准的电量变成标准的电信号,如4—20mA、1—5V、0—10V等等。 9 E( E% b6 N* [! ^0 N8 ~
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同时还要有模拟量输入单元(A/D),把这些标准的电信号变换成数字信号;模拟量输出单元(D/A),以把PLC处理后的数字量变换成模拟量——标准的电信号。 5 H/ I  I- [9 g: P7 L* J
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所以标准电信号、数字量之间的转换就要用到各种运算。这就需要搞清楚模拟量单元的分辨率以及标准的电信号。例如:
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PLC模拟单元的分辨率是1/32767,对应的标准电量是0—10V,所要检测的是温度值0—100℃。那么0—32767对应0—100℃的温度值。然后计算出1℃所对应的数字量是327.67。假如想把温度值精确到0.1℃,把327.67/10即可。
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4 }: h0 l0 v, c9 f3 y( |, y4 g9 k模拟量控制包括:反馈控制、前馈控制、比例控制、模糊控制等。这些都是PLC内部数字量的计算过程。
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3、 脉冲量是其取值总是不断的在0(低电平)和1(高电平)之间交替变化的数字量。每秒钟脉冲交替变化的次数称为频率。 8 m) J) S; W  z& ^

0 d) Q! n# v" K8 @  fPLC脉冲量的控制目的主要是位置控制、运动控制、轨迹控制等。例如:脉冲数在角度控制中的应用。步进电机驱动器的细分是每圈10000,要求步进电机旋转90度。那么所要动作的脉冲数值=10000/(360/90)=2500。- S6 [6 A8 U. l3 u3 a7 M
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发表于 2013-9-16 04:37:25 | 显示全部楼层

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