含(han)有(you)(you)(you)飽和溶(rong)解(jie)氧(yang)(yang)(yang)的(de)水(shui)樣進入測定(ding)(ding)(ding)槽并與生(sheng)物(wu)傳感器接觸。當(dang)水(shui)樣中(zhong)沒有(you)(you)(you)可生(sheng)物(wu)降解(jie)的(de)有(you)(you)(you)機(ji)物(wu)時，當(dang)溶(rong)解(jie)氧(yang)(yang)(yang)向氧(yang)(yang)(yang)電(dian)極的(de)擴(kuo)(kuo)散速(su)率(lv)（質量）達到(dao)恒(heng)定(ding)(ding)(ding)時，就(jiu)會產生(sheng)恒(heng)定(ding)(ding)(ding)電(dian)流。當(dang)水(shui)樣中(zhong)存在可生(sheng)物(wu)降解(jie)的(de)有(you)(you)(you)機(ji)物(wu)時，有(you)(you)(you)機(ji)物(wu)被生(sheng)物(wu)膜中(zhong)的(de)微生(sheng)物(wu)同化(hua)，微生(sheng)物(wu)的(de)細胞呼吸(xi)作(zuo)用也增(zeng)強，消耗了一部(bu)分溶(rong)解(jie)氧(yang)(yang)(yang)，減(jian)少了擴(kuo)(kuo)散到(dao)氧(yang)(yang)(yang)電(dian)極表面(mian)上的(de)溶(rong)解(jie)氧(yang)(yang)(yang)。當(dang)水(shui)樣中(zhong)溶(rong)解(jie)氧(yang)(yang)(yang)向電(dian)極的(de)擴(kuo)(kuo)散速(su)率(lv)（質量）再次達到(dao)恒(heng)定(ding)(ding)(ding)時，就(jiu)又(you)會產生(sheng)恒(heng)定(ding)(ding)(ding)電(dian)流。 由(you)于兩個恒(heng)流的(de)差值與水(shui)樣中(zhong)可生(sheng)物(wu)降解(jie)有(you)(you)(you)機(ji)物(wu)的(de)濃度有(you)(you)(you)定(ding)(ding)(ding)量關系，因此電(dian)流信號經微機(ji)放大、分析處理(li)后，直接顯示BOD檢測結果。