IC660MLA105，，IC660MLA105，IC660MLA105
PLC與繼電器控制邏輯的性能和價格8大方面的比較
① 控制邏輯：繼電器控制邏輯采用硬接線邏輯，利用繼電器機械觸點的串聯或并聯及延時繼電器的滯后動作等組合成控制邏輯，其連線多而復雜，體積大，功耗大，一旦系統構成后，想再改變或增加功能都很困難。另外繼電器觸點數目有限，每只一般只有4～8對觸點，因此靈活性和擴展性都很差。而PLC采用存儲邏輯，其控制邏輯以程序方式存儲在內存中，要改變控制邏輯，只需改變程序，故稱為“軟接線”，其連線少，體積小，加之PLC中每只軟繼電器的觸點數理論上無限制，因此靈活性和擴展性都很好。PLC由中大規模集成電路組成，功耗小。
② 工作方式：當電流接通時，繼電控制線路中各繼電器都處于受約狀態，即該吸合的都應吸合，不該吸合的都因受某種條件限制不能吸合。而PLC的控制邏輯中，各繼電器都處于周期性循環掃描接通之中，從宏觀上看，每個繼電器受制約接通的時間是短暫的。
③ 控制速度：繼電控制邏輯依靠觸點的機械動作實現控制，工作頻率低。觸點的開閉動作一般在幾十毫秒數量級。另外機械觸點還會出現抖動問題。而PLC是由程序指令控制半導體電路來實現控制的，速度極快，一般一條用戶指令的執行時間在微秒數量級。PLC內部還有嚴格的同步，不會出現抖動問題。
④ 限時控制：繼電控制邏輯利用時間繼電器的滯后動作進行限時控制。時間繼電器一般分為空氣阻尼式、電磁式、半導體式等，其定時精度不高，定時時間易受環境濕度和溫度變化的影響，調整時間困難。有些特殊的時間繼電器結構復雜，不便維護。
PLC使用半導體集成電路作定時器，時基脈沖由晶體振蕩器產生，精度相當高，定時范圍一般從0.1 s到若干分鐘甚至更長，用戶可根據需要在程序中設定定時值，然后由軟件和硬件計數器來控制定時時間，定時精度小于10 ms且定時時間不受環境的影響。
⑤ 計數控制：PLC能實現計數功能，而繼電控制邏輯一般不具備計數控制功能。
⑥ 設計與施工：使用繼電控制邏輯完成一項控制工程，其設計、施工、調試必須依次進行，周期長，而且修改困難。工程越大，這一點就越突出。而用PLC完成一項控制工程，在系統設計完成以后，現場施工和控制邏輯的設計(包括梯形圖和程序設計)可以同時進行，周期短，且調試和修改都很方便。
⑦ 可靠性和可維護性：繼電控制邏輯使用了大量的機械觸點，連線也多。觸點開閉時會受到電弧的損壞，并有機械磨損，壽命短，因此可靠性和可維護性差。而PLC采用微電子技術，大量的開關動作由無觸點的半導體電路來完成，它體積小、壽命長、可靠性高。PLC還配備有自檢和監督功能，能檢查出自身的故障，并隨時顯示給操作人員，還能動態地監視控制程序的執行情況，為現場調試和維護提供了方便。
⑧ 價格：繼電控制邏輯使用機械開關、繼電器和接觸器，價格比較便宜。而PLC使用中大規模集成電路，價格比較昂貴。
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TESTED!!
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