在选择方案时，应考虑尽量减少控制元件数、接点数和焊点数，以降低系统的失效率。采用可编程控制器（PC）来代替由继电器等组成的控制柜可以提高系统的可靠性。在比较可编程序控制器和继电器控制柜两种方案时，除了购置价格以外，还应充分估计前者在提高可靠性、缩短开发周期和减小工作量以及节省维修时间等有利因素。为了减少系统的早期失效，机床制造厂可以对控制元件进行筛选，即使每台元件在实际使用条件下连续工作一定次数，把失效产品排除，以减少装到系统中的元件早期失效。元件进入耗损失效期以后，失效率将明显上升。为了防止这种情况影响系统的可靠性，可以在有效寿命（或偶然故障期）将结束时，不管元件是否损坏，也进行更换。采用筛选和预防性更换，可以保证系统中的元件工作在偶然失效期内，在这个前提下才可以用元件的偶然失效率来计算系统的失效率。
提高可靠性的办法，从根本上来说，应以现场失效调查和分析着手。和一般的产品设计和计算工作不同，可靠性设计不可能只通过理论和计算取得需要的结果，保证可靠性的程度取决于对使用现场实际发生的失效的了解（包括其深度和广度）。实验室试验也是取得失效数据的一个方法，但由于试验的内容、方法和条件限制，故只能是对现场使用情况的一个近似的模拟，它不可能代替使用现场失效情况的调查分析。脱离了现场条件的可靠性试验是没有实际意义的。
PLC可靠不等于PLC控制系统可靠。PLC控制系统比单独的PLC复杂。系统复杂，出现故障的可能性就大，可靠性将降低。PLC控制系统不是PLC及其被控对象简单地相加，而是两者有机的结合。结合得好，才可靠。PLC控制系统也不等于PLC及其被控对象全面结合，只是与实施控制有关的才需要结合。
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CONTROL TECHNOLOGY 2214 2 AXIS SERVO MODULE
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HEDLAND STAINLESS FLOWMETER 1/2'' FLOW RATE .3 TO 2.0
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TOSHIBA TOSVERT VT130G2 2025 TRANSISTOR INVERTER (2HP)
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SIEMENS 6SE7090-0XX84-0KA0 WITH 6SE7090-0XX84-0FA0
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FANUC A860-0320-T111 PULSE CODER GOOD TAKE OFF
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HARDMEIER CONTROL DV 1Q DRIVE CH-8307 NEW IN BOX
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YASKAWA JANCD-MM13 DF8203076/A0 MOTOMAN MEMORY BOARD
YASKAWA JANCD-HA03 REV.B MOTOMAN CARD *XLNT*
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SIEMENS 6SE7090-0XX84-0KA0 WITH 6SE7090-0XX84-0FA0
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