8 V0 O) }* A. f$ A; ?. e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。 3 a6 j. ~ X/ `
. z. i, e0 a: u v; ~2 Z2 G! o0 ]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。 - M6 v# p. {: n9 @# n0 i4 z8 _0 E
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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。 + M0 g1 [, X# y! S
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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： 3 J, |% O9 z. U# C* m) U" a3 J- a( A
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。 ) v+ b5 j! N) `2 p6 c* n! W' M0 O1 t# m: u7 R* V& R( f! X
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。 $ C) b9 U: K8 V8 k- `# f
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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。 6 g: I r8 L3 K% j. Z" s) N. q / R$ i( {% Q& \! t8 _& yPLC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。 ( ?3 X/ h+ H( G" r作者: john8982 时间: 2013-9-16 04:37 标题: iphone case uk we should contact Albany. run entirely by volunteers6 t0 m! \/ N8 y4 B* `8 k i
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