安全栅防爆元件的应用
工业上的酒精、汽油等可燃物品的生产和使用都涉及到防爆技术。常用的防爆技术包括：隔爆、本质安全、油浸、充砂、浇封等。在电气防爆中，本质安全是使用最多的技术，它要用到一个关键元件——安全栅。本文包括如下两个主题：安全栅的作用及分类；
1、安全栅的作用及分类在电气本质安全防爆(简称：本安防爆)中，一般我们把工作场所分为防爆区域和非防爆区域。防爆区域和非防爆区域之间有电能的传输，比如，防爆区域的开关、按钮、传感器等通过电线与放置在非防爆区域电气柜中的PLC相连接。安全栅的作用就是在防爆区和非防爆区之间起到能量限流的作用，它降低防爆区域内信号的电能，从而降低其产生电火花的风险。安全栅根据结构的不同，分为齐纳式安全栅(Zener Safety barrier)和隔离式安全栅(Isolated Safety barrier)两类。齐纳式安全栅在其内部电路中串联快速熔断丝、限流电阻和并联限压齐纳二极管，从而实现限制能量的作用，它具有如下一些特点：①必须有单独的、非常可靠的接地系统(本安系统接地)，接地电阻应小于1Ω；
②不能进行电信号转换，对于热电偶/热电阻(RTD)等信号可能会由于电磁干扰而出现错误，因此不适合连接该类型的传感器；
③对供电电源电压影响非常大，电源电压的波动可能会引起齐纳二极管的电流泄漏，从而引起信号的误差或者发出错误电平，严重时会使快速保险丝烧断而永久损坏。按规定齐纳式安全栅内部齐纳管、限流电阻、保险丝整体浇封，一旦损坏无法修复；
④体积小，价格便宜，不需要额外供电；
隔离式安全栅的输入、输出及电源三者之间相互隔离，它具有如下一些特点：
①不需要接地线，现场施工非常方便；
②由于信号线无需共地，使得整个系统的稳定性和抗干扰能力大大增强；
③具有信号转换能力，可以处理热电偶/热电阻/频率等信号，比如将其转换成4~20mA的电流信号输出，抗干扰能力比较强；
④一般隔离式安全栅具有两路输出通道，相互之间电气隔离，互不影响；
⑤价格相对贵些，需要外部供电；
虽然隔离式安全栅价格相对较贵，但其出色的性能和便于施工的特点，使得在工业现场有广泛的应用。接下来我们介绍下倍加福(P+F)公司的一款隔离式安全栅产品。
2、倍加福隔离式安全栅介绍
下面以此品牌为例，倍加福(P+F)的KFD2-ST2-Ex2隔离式安全栅用于开关量信号输入，其外观如下图所示：
它有两路隔离式通道，可以连接干接点开关信号，需要外部24V电源供电。模块上、下各有两个接线端子，其中：
引脚1、2、3和7为通道1；引脚4、5、6和9为通道2；14、15为24V电源；
接线原理图如下图所示：
以通道1的使用为例，接线时将引脚1和3连接防爆区域的开关，将引脚7连接到非防爆区域的PLC输入通道，14接24V电源正极，15接负极。好了，关于安全栅就介绍到这里。
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