PU514A 3BSE032400R1控制器模块
,, 以及损坏这些盖的机加工表面都是主要的例子。本质安全系统现在被认为是在爆炸环境中提供自动控制功能的更理想的方法。该技术依赖于电子电路的固有参数，因此在正常或异常操作条件下，不会释放出足以点燃特定大气混合物的能量。为了设计有效的本质安全系统，必须限制进入危险区域的能源。对于电子控制，通过控制可能进入危险区域的电压和电流来实现能量限制。此外，控制装置中储存的电能被限制在不能引起给定大气点燃的水平。本质安全系统克服了“防爆”系统的缺点，通过在安全区域正确安装本质安全齐纳二极管屏障，实际上消除了爆炸的可能性。本质安全齐纳二极管安全栅必须安装在电源线、负载供应线以及使用5500系列电流源（PNP）开路集电极时的信号返回线中。危险场所概述（有关完整定义，请参考国家电气规范出版物NFPA第70-78号）I类场所，其中空气中存在或可能存在足以产生爆炸性或可燃性混合物的易燃气体或蒸汽。由于存在可燃性粉尘而具有危险性的II类场所。III类位置，由于存在易点燃的纤维或飞边而具有危险性，但此类纤维或飞线不存在
and damaging the machined surfaces of such covers are all prime examples. Intrinsically Safe systems are now recognized as a more highly desirable means of providing automated control functions in explosive environments. The technique relies on the inherent parameters of electronic circuits, so that no energy can be released under normal or abnormal operating conditions, of sufficient magnitude to ignite a specified atmospheric mixture. To design an effective Intrinsically Safe system, energy sources that enter the hazardous area must be limited. For electronic controls, energy limiting is accomplished by controlling the voltages and currents that may enter the hazardous area. In addition, stored electrical energy in the controls is limited to levels that cannot cause ignition of a given atmosphere. An Intrinsically Safe system overcomes the shortcomings of the “explosion-proof ” system and virtually eliminates the probability of explosion by properly installing Intrinsic Safety Zener Diode Barriers in the safe area. Intrinsic Safety Zener Diode Barriers must be installed in the power supply line, the load supply line and when using the current source (PNP) open collector of the Series 5500, in the signal return line. Summary of Hazardous Locations (For full and complete definitions, consult the National Electric Code publication NFPA No. 70--78.) Class I Locations in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class II Locations which are hazardous because of the presence of combustible dust. Class III Locations which are hazardous because of the presence of easily ignitable fibers or flyings, but in which such fibers or flyings are not
