描述
為監(jiān)控PLC運(yùn)行程序是否正常,PLC系統(tǒng)都設(shè)置了”看門狗”(Watchingdog)監(jiān)控程序。運(yùn)行用戶程序開始時,先清”看門狗”定時器,并開始計時。當(dāng)用戶程序一個循環(huán)運(yùn)行完了,則查看定時器的計時值。若超時(一般不超過100ms),則報警。嚴(yán)重超時,還可使PLC停止工作。用戶可依報警信號采取相應(yīng)的應(yīng)急措施。定時器的計時值若不超時,則重復(fù)起始的過程,PLC將正常工作。顯然,有了這個”看門狗”監(jiān)控程序,可保證PLC用戶程序的正常運(yùn)行,可避免出現(xiàn)”死循環(huán)”而影響其工作的可靠性。
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