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定时器基本知识

2014/8/12 10:05:31点击:

人类最早使用的定时工具是沙漏或水漏,但在钟表诞生发展成熟之后,人们开始尝试使用这种全新的计时工具来改进定时器,达到准确控制时间的目的。定时器确实是一项了不起的发明,使相当多需要人控制时间的工作变得简单了许多。定时器甚至用在了军事方面,制成了定时炸弹,定时雷管。现在的不少家用电器都安装了定时器来控制开关或工作时间。

定时器主要分为以下几种

1、 接通延时型定时器:接通延时型定时器是各种PLC中最常见最基本的定时器,这种定时器在 SIEMENS的PLC中,称为SD型定时器。
2、 断开延时型定时器:这种定时器是当输入条件00000为ON时无延时作用,只有在输入条件00000为OFF时产生延时作用。在SIEMENS的PLC中,称为SF型定时器。
3、保持型接通延时定时器:这种定时器是当输入条件00000为ON后,即产生锁存功能,即使输入条件00000又变为OFF,仍视输入条件为ON,当定时器的当前值等于设定值时,定时器动作,这种定时器在SIEMENS的PLC中,称为SS型定时器。
4、脉冲型定时器:这种定时器是当输入条件00000为ON后,定时器即时动作,但经过定时器所设定的时间后,即使输入条件00000仍为ON,定时器却变为OFF状态。即这种定时器ON状态的维持时间是由设定值决定的。如果00000为ON的时续时间小于定时器的设定值,定时器的ON状态维持时间为输入条件00000为ON的持续时间。这种定时器在SIEMENS的PLC中,称为SP型定时器。
5、扩张型脉冲定时器:这种定时器与脉冲型定时器的区别是,只要输入条件00000出现了ON状态,不管其持续时间多长,均可使定时器为ON的维持的时间与定时器的设定值一致。这种定时器在SIEMENS的PLC中,称为SE型定时器。