對于重要的控制回路,可以采用手動(dòng)后備的方法來提高可靠性。一旦自動(dòng)控制失靈,用手動(dòng)操作站直接進(jìn)行操作,在這種情況下,手動(dòng)操作站直接輸出4~20mA或1~5V的模擬量信號(hào)去控制執(zhí)行機(jī)構(gòu)或直接接地進(jìn)行設(shè)備的操作,可以手動(dòng)控制生產(chǎn)過程。
?、?自動(dòng)后備
自動(dòng)后備是采用冗余的方式設(shè)置另外一套或幾套備用控制裝置。當(dāng)處于運(yùn)行狀態(tài)的自動(dòng)控制裝置發(fā)生故障時(shí),備用控制裝置自動(dòng)投入,維持系統(tǒng)的自動(dòng)控制。自動(dòng)后備是冗余系統(tǒng)的一種形式,冗余有主控單元冗余、電源系統(tǒng)冗余、網(wǎng)絡(luò)冗余、I/O模塊冗余、操作員站冗余、服務(wù)器冗余等。運(yùn)行設(shè)備出現(xiàn)
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