圖4-49是由兩個(gè)計(jì)數(shù)器組成的延時(shí)電路。輸入Ⅹ0端接通后，CT100開始對(duì)R901C（1s時(shí)鐘脈沖）進(jìn)行減計(jì)數(shù)。經(jīng)過20s，CT100有輸出，其常開觸點(diǎn)C100閉合。CT101對(duì)C100常開觸點(diǎn)的動(dòng)作計(jì)數(shù)一次。與此同時(shí)C100常開觸點(diǎn)也將CT100復(fù)位，C100常開觸點(diǎn)又?jǐn)嚅_，CT100繼續(xù)對(duì)R901C計(jì)數(shù)。又經(jīng)過20s，CT101又對(duì)C100常開觸點(diǎn)計(jì)數(shù)一次……。如此循環(huán)，經(jīng)過20s×30＝600s后，CT101有輸出，其常開觸點(diǎn)C101閉合，接通輸出繼電器Y0。

圖4-49 采用計(jì)數(shù)器組成的延時(shí)電路