可編程控制器PLC運行時可能會出現死機的情況，這給工業生產造成不可預估的損失，因此，先要了解PLC死機的原因，針對原因進行排查，軟件或硬件錯誤都有可能導致PLC死機，下面分別進行介紹：

    1、硬件方面 

    （1）I／O竄電，PLC自動偵測到I／O錯誤，進入STOP模式。 

    （2）I／O損壞，程序運行到需要該I／O的反饋信號，不能向下執行指令。 

    （3）擴展模塊(功能型，如A／D)線路干擾或開路等。 

    （4）電源部分有干擾或故障。 

    （5）PLC的連接模塊及地址分配模塊出故障。 

    （6）電纜引起的故障。 

    2、軟件方面 

    （1）觸發了死循環。 

    （2）程序改寫了系統參數區的內容，卻沒有初始化部分。 

    （3）保護程序啟動：硬件保護、限制使用時間(針對貨款收回) 

    （4）數據溢出，步長過大、看門狗 (可修改DOG時間)動作。
ALLEN BRADLEY 1747-L20G 20 I/O FIXED HARDWARE 
ALLEN BRADLEY 1747-L20L 20 I/O FIXED HDWR STYLE, 12 DC SOURCE IN W/ HSC & 8 TRANS. SINK OUT, AC LINE PWR, 
ALLEN BRADLEY 1747-L20R 20 I/O FIXED HARDWARE 
ALLEN BRADLEY 1747-L20P 20 I/O FIXED HARDWARE 
ALLEN BRADLEY 1747-L20R 20 I/O FIXED HARDWARE 
ALLEN BRADLEY 1747-L30A 30 I/OFIXED HDWR STYLE, 18 120 V AC IN & 12 RELAY OUT, AC LINE PWR, 
ALLEN BRADLEY 1747-L30B 30 I/OFIXED HDWR STYLE, 18 120 V AC IN & 12 RELAY OUT, AC LINE PWR, 
ALLEN BRADLEY 1747-L40A 40 I/OFIXED HDWR STYLE, 18 120 V AC IN & 12 RELAY OUT, AC LINE PWR, 
ALLEN BRADLEY 1747-L40B 40 I/O FIXED HDWR STYLE 24 120 V IN & 16 TRIAC OUT, AC LINE PWR, 
ALLEN BRADLEY 1747-L40C 40 I/O FIXED HDWR STYLE 24 DC SINK IN W/HSC & 16 RELAY OUT, AC LINE PWR 
ALLEN BRADLEY 1747-L40E 40 I/O FIXED HDWR STYLE 24 DC SINK IN W/HSC & 16 RELAY OUT, AC LINE PWR 
ALLEN BRADLEY 1747-L40F 40 I/O FIXED HDWR STYLE 24 DC SINK IN W/HSC & 16 RELAY OUT, AC LINE PWR 
ALLEN BRADLEY 1747-L40L 40 I/O FIXED HDWR STYLE 24 DC SINK IN W/HSC & 16 RELAY OUT, AC LINE PWR 
ALLEN BRADLEY 1747-L40P 40 I/O FIXED HDWR STYLE 24 DC SINK IN W/HSC & 16 RELAY OUT, AC LINE PWR 
ALLEN BRADLEY 1747-L511 SLC 5/01 CPU, 1K USR MEMORY 
ALLEN BRADLEY 1747-L514 SLC 5/01 CPU, 4K USR MEMORY 
ALLEN BRADLEY 1747-L524 SLC 5/02 CPU, 4K USR MEMORY 
ALLEN BRADLEY 1747-L531 SLC 5/03 
ALLEN BRADLEY 1747-L532 SLC 5/03 CPU, 12K USR INSTRUCT. CAPACITY 
ALLEN BRADLEY 1747-L541 SLC 5/04 
ALLEN BRADLEY 1747-L542 SLC 5/02 CPU, 4K USR MEMORY 
ALLEN BRADLEY 1747-L542P 5/04P PROCESSER 
ALLEN BRADLEY 1747-L543 CONTROLLER,64K MEMORY 
ALLEN BRADLEY 1747-L551 CONTROLLER,64K MEMORY 
ALLEN BRADLEY 1747-L552 CONTROLLER,64K MEMORY 
ALLEN BRADLEY 1747-L553 CONTROLLER,64K MEMORY 
ALLEN BRADLEY 1747-M1 EEPROM MEMORY MODULE,1K