PLC的控制方式屬于存儲程序控制，其控制功能是通過存放在存儲器內(nèi)的程序來實現(xiàn)的，若要對控制功能作必要修改，只需改變控制程序即可，這就實現(xiàn)了控制的軟件化。可編程控制器的優(yōu)點在于"可"字，從軟件來講，其控制程序可編輯、可修改；從硬件上講，其外部設備配置可變。構(gòu)建一個PLC控制系統(tǒng)的重心就在于控制程序的編制，但外部設備的選用也將對程序的編制產(chǎn)生影響。因此在進行程序設計時應結(jié)合實際需要，硬、軟件綜合考慮。本文就硬、軟兩方面，選取梯形圖為編程語言，以松下電工FPO-C32型PLC為例，對PLC使用過程中易出現(xiàn)的幾個問題及解決方法進行了分析。
一、外部輸入設備的選用與PLC輸入繼電器的使用
1. 外部輸入信號的采集
PLC的外部設備主要是指控制系統(tǒng)中的輸入輸出設備，其中輸人設備是對系統(tǒng)發(fā)出各種控制信號的主令電器，在編寫控制程序時必須注意外部輸入設備使用的是常開還是常閉觸點，并以此為基礎進行程序編制。否則易出現(xiàn)控制錯誤。
在PLC內(nèi)部存儲器中有專用于輸入狀態(tài)存儲的輸入繼電器區(qū)，各輸入設備（開關、按鈕、行程開關或傳感器信號）的狀態(tài)經(jīng)由輸入接口電路存儲在該區(qū)域內(nèi)，每個輸入繼電器可存儲一個輸入設備狀態(tài)。PLC中使用的"繼電器"并非實體繼電器，而是"軟繼電器"，可提供無數(shù)個常開、常閉觸點用于編程。每個"軟繼電器"僅對應PLC存儲單元中的一位（bit），該位狀態(tài)為"1"，表示該"軟繼電器線圈"通電，則程序中所有該繼電器的觸點都動作。輸入繼電器作為PLC接收外部主令信號的器件，通過接線與外部輸入設備相聯(lián)系，其"線圈"狀態(tài)只能由外部輸入信號驅(qū)動。
LSE3A Trutzschler Light Bar Transmitter
LSE3A Trutzschler Light Bar Transmitter
Korjo Zippered Plastic Bags in 3 Colors -ZPB23
Korjo Zippered Plastic Bags in 3 Colors -ZPB23
Hidraulikpumpe S12293922 ZPB10,5/10,5/8,3D
Hidraulikpumpe S12293922 ZPB10,5/10,5/8,3D
EMPORIO ARMANI EA7 GIUBBOTTO GIUBBINO UOMO NUOVO ORIGINALE NERO B29
EMPORIO ARMANI EA7 GIUBBOTTO GIUBBINO UOMO NUOVO ORIGINALE NERO B29
Electrical Equipment & Supplies (1)
EA7 EMPORIO ARMANI BOMBER JACKET Blu mis-XL
EA7 EMPORIO ARMANI BOMBER JACKET Blu mis-XL
trutzschler ZPB3 9 495-12.430.000 AD 495-12.230.001 AE 495-12.230.002 AF CPU
trutzschler ZPB3 9 495-12.430.000 AD 495-12.230.001 AE 495-12.230.002 AF CPU
TRUTZSCHLER ZPB 2 ZPB2 CIRCUIT BOARD CARD PLC MODULE 9 408-00.810.000 AG
TRUTZSCHLER ZPB 2 ZPB2 CIRCUIT BOARD CARD PLC MODULE 9 408-00.810.000 AG
TRUTZSCHLER ZPB 2 ZPB2 CIRCUIT BOARD 9 400-20.810.110 AE A-03-21-1 NEW
TRUTZSCHLER ZPB 2 ZPB2 CIRCUIT BOARD 9 400-20.810.110 AE A-03-21-1 NEW
Trutzschler ZPB 2 400-20.810.110AE
Trutzschler ZPB 2 400-20.810.110AE
Trutzschler SIB 3 (A1) Board ——#9
Trutzschler SIB 3 (A1) Board ——#9
TRUTZSCHLER SBG-1 SBG1 CIRCUIT BOARD CARD 9 493-37.230.000 AA 49337230000 AA
TRUTZSCHLER SBG-1 SBG1 CIRCUIT BOARD CARD 9 493-37.230.000 AA 49337230000 AA
Trutzschler RIB 1 490-18.330.000 Lifetime Warranty !!!
Trutzschler RIB 1 490-18.330.000 Lifetime Warranty !!!
TRUTZSCHLER PR-1 CIRCUIT BOARD CARD PLC 491-89.230.000 49189230000
TRUTZSCHLER PR-1 CIRCUIT BOARD CARD PLC 491-89.230.000 49189230000
Trutzschler power supply VNB 1 9 494-66.430.000 AB VNB1 949466430000 NEW 8 A 24V
Trutzschler power supply VNB 1 9 494-66.430.000 AB VNB1 949466430000 NEW 8 A 24V
Trutzschler Power Supply NTE 1 9 492-47.430.000 AF New
Trutzschler Power Supply NTE 1 9 492-47.430.000 AF New
Trutzschler PLC Control Station BRE 1C 493-55.332.000 Used
Trutzschler PLC Control Station BRE 1C 493-55.332.000 Used
TRUTZSCHLER KOM 1.2 1 CIRCUIT BOARD 492-40.230.002 492-40.431.000 492-40.230.001
TRUTZSCHLER KOM 1.2 1 CIRCUIT BOARD 492-40.230.002 492-40.431.000 492-40.230.001
TRUTZSCHLER KOM 1 CIRCUIT BOARD 492-40.230.001 492-40.431.000 492-40.230.002. 3A
TRUTZSCHLER KOM 1 CIRCUIT BOARD 492-40.230.001 492-40.431.000 492-40.230.002. 3A
Trutzschler KIB 1A 9 494-61.230.000 Lifetime Warranty !!!
Trutzschler KIB 1A 9 494-61.230.000 Lifetime Warranty !!!
TRUTZSCHLER GMB-1C GMB1C CIRCUIT BOARD CARD 9 494-58.332.000 AC 49458332000
TRUTZSCHLER GMB-1C GMB1C CIRCUIT BOARD CARD 9 494-58.332.000 AC 49458332000
TRUTZSCHLER GMB-1A-9-494-58.230.000 / GMB1A949458230000 (USED TESTED CLEANED)
TRUTZSCHLER GMB-1A-9-494-58.230.000 / GMB1A949458230000 (USED TESTED CLEANED)
TRUTZSCHLER GMB 1B CIRCUIT BREAKER Q067173 WITH HEAT BLOCK $149
TRUTZSCHLER GMB 1B CIRCUIT BREAKER Q067173 WITH HEAT BLOCK $149
Trutzschler Drive Motor - 1LA7166-4AA99-ZN15
Trutzschler Drive Motor - 1LA7166-4AA99-ZN15
Trutzschler Drive FU1 9 495-20.330.00 AA 9 494-70.019.501 Used
Trutzschler Drive FU1 9 495-20.330.00 AA 9 494-70.019.501 Used
TRUTZSCHLER DEG 1 9 494-00.330.000AA, I/O BLOCK CIRCUIT BOARD
TRUTZSCHLER DEG 1 9 494-00.330.000AA, I/O BLOCK CIRCUIT BOARD
Trutzschler DEG 1 9 494-00.330.000AA One Year Warranty !
Trutzschler DEG 1 9 494-00.330.000AA One Year Warranty !
TRUTZSCHLER DEG 1 9 494-00.330.000AA I/O BLOCK CIRCUIT BOARD NEW NOS $899
TRUTZSCHLER DEG 1 9 494-00.330.000AA I/O BLOCK CIRCUIT BOARD NEW NOS $899
Trutzschler DCB1 DCB 1 9 494-80.230.000 ABR28 494-16.210.001 AA
Trutzschler DCB1 DCB 1 9 494-80.230.000 ABR28 494-16.210.001 AA
TRUTZSCHLER CONTROL STATION BRE 1C, 9 493-55.332.000 AD
TRUTZSCHLER CONTROL STATION BRE 1C, 9 493-55.332.000 AD
TRUTZSCHLER CIRCUIT BOARD CARD RAK 1 9 492-58.430.000
TRUTZSCHLER CIRCUIT BOARD CARD RAK 1 9 492-58.430.000
TRUTZSCHLER CIRCUIT BOARD CARD PLC MODULE CCM-UE1 CCMUE1 9 491-91.230.000
TRUTZSCHLER CIRCUIT BOARD CARD PLC MODULE CCM-UE1 CCMUE1 9 491-91.230.000
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