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(shè)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(shè)備的選用也將對程序的編制產(chǎn)生影響。因此在進(jìn)行程序設(shè)計時應(yīng)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(jìn)行了分析。
一、外部輸入設(shè)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(shè)備主要是指控制系統(tǒng)中的輸入輸出設(shè)備，其中輸人設(shè)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(shè)備使用的是常開還是常閉觸點，并以此為基礎(chǔ)進(jìn)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(shè)備（開關(guān)、按鈕、行程開關(guān)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(shè)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(yīng)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(shè)備相聯(lián)系，其"線圈"狀態(tài)只能由外部輸入信號驅(qū)動。
Woodward SPM-A Synchronizer Module, 9905-001 F
Woodward SPM-A Synchronizer Module, 9905-001 F
Woodward SPM-A Synchronizer 9905-003 Rev. R
Woodward SPM-A Synchronizer 9905-003 Rev. R
WOODWARD SPM-A SYNCHRONIZER 9905-002
WOODWARD SPM-A SYNCHRONIZER 9905-002
Woodward SPM-A Synchronizer 9905-001 M Rev.M 10W 50/60Hz 115/230V Used And Works
Woodward SPM-A Synchronizer 9905-001 M Rev.M 10W 50/60Hz 115/230V Used And Works
Woodward SPM-A Synchronizer / Part # 9905-001 rev N.
Woodward SPM-A Synchronizer / Part # 9905-001 rev N.
WOODWARD SPEED AND PHASE MATCHING SYNCHRONIZER SEVERAL MODELS AVAILABLE
WOODWARD SPEED AND PHASE MATCHING SYNCHRONIZER SEVERAL MODELS AVAILABLE
WOODWARD PEAK 150 DIGITAL STEAM TURBINE CONTROL 9905-867 NEW IN BOX
Woodward Load Sharing Module, 9905-726
Woodward Load Sharing Module, 9905-726
Woodward Load Sharing Module 9905-726
Woodward Load Sharing Module 9905-726
WOODWARD LOAD SHARING MODULE
WOODWARD LOAD SHARING MODULE
Woodward Governor Load Sharing &speed Control 2301A
Woodward Governor Load Sharing &speed Control 2301A
WOODWARD CONTROL AGLC 9905-096
WOODWARD CONTROL AGLC 9905-096
WOODWARD AUTOMATIC GENERATOR LOADING CONTROL
WOODWARD AUTOMATIC GENERATOR LOADING CONTROL
WOODWARD 9905-992 / 9905992 (USED TESTED CLEANED)
WOODWARD 9905-992 / 9905992 (USED TESTED CLEANED)
WOODWARD 9905-970 REV. L LINKNET 6 CHANNEL * NEW IN BOX *
WOODWARD 9905-970 REV. L LINKNET 6 CHANNEL * NEW IN BOX *
WOODWARD 9905-970 LINKNET 6 CHANNEL *NEW NO BOX*
WOODWARD 9905-970 LINKNET 6 CHANNEL *NEW NO BOX*
WOODWARD 9905-760 LINKNET TERMINATION MODULE * NEW IN BOX *
WOODWARD 9905-760 LINKNET TERMINATION MODULE * NEW IN BOX *
WOODWARD 9905-110 / 9905110 (USED TESTED CLEANED)
WOODWARD 9905-110 / 9905110 (USED TESTED CLEANED)
Woodward 9905-096 Automatic Generator Loading Control Rev. L, 115/230 VAC Supply
Woodward 9905-096 Automatic Generator Loading Control Rev. L, 115/230 VAC Supply
Woodward 9905-096 Automatic Generator Loading Control 115/230 VAC Supply
Woodward 9905-096 Automatic Generator Loading Control 115/230 VAC Supply
WOODWARD 9905-001 REV N SPM-A SYNCHRONIZER *USED*
WOODWARD 9905-001 REV N SPM-A SYNCHRONIZER *USED*
Woodward 2301A Low Voltage Load Sharing and Speed Control 9905-377 USED
Woodward 2301A Low Voltage Load Sharing and Speed Control 9905-377 USED
Vintage Bundeswehr BRD Warndreieck 9905-12-148-7363 mit original Hülle
Vintage Bundeswehr BRD Warndreieck 9905-12-148-7363 mit original Hülle
USED Woodward 9905-373 Digital Synchronizer and Load Control Rev. P
USED Woodward 9905-373 Digital Synchronizer and Load Control Rev. P
USED Woodward 9905-001 SPM-A Synchronizer Module Rev. L
USED Woodward 9905-001 SPM-A Synchronizer Module Rev. L
Reflex Reflector HELLA 8RA 002 016-121
Reflex Reflector HELLA 8RA 002 016-121
PAGID FRONT AXLE INTERNALLY VENTED BRAKE DISCS 54487 ?? 276 mm BRAKE KIT BRAKES
PAGID FRONT AXLE INTERNALLY VENTED BRAKE DISCS 54487 ?? 276 mm BRAKE KIT BRAKES
OE Hella SIDE & REAR LAMP ROUND REFLECTOR RED 8RA002016-111 88020
OE Hella SIDE & REAR LAMP ROUND REFLECTOR RED 8RA002016-111 88020
OE Hella SIDE & REAR LAMP REFLECTOR 8RA 002 016-121 / 8RA002016-121 88038
OE Hella SIDE & REAR LAMP REFLECTOR 8RA 002 016-121 / 8RA002016-121 88038
NEW Woodward 9905-795 Rev.M. Digital Synchronizer And Load Control. Factory Seal
NEW Woodward 9905-795 Rev.M. Digital Synchronizer And Load Control. Factory Seal
Highway Warning Triangle Set of 3 NSN: 9905-01-148-9546
Highway Warning Triangle Set of 3 NSN: 9905-01-148-9546
GENUINE PAGID FRONT AND REAR AXLE BRAKE KIT BRAKE DISCS BRAKE PAD SET BRAKE PADS
GENUINE PAGID FRONT AND REAR AXLE BRAKE KIT BRAKE DISCS BRAKE PAD SET BRAKE PADS
GENUINE PAGID FRONT AND REAR AXLE BRAKE KIT BRAKE DISCS BRAKE PAD SET BRAKE PADS
GENUINE PAGID FRONT AND REAR AXLE BRAKE KIT BRAKE DISCS BRAKE PAD SET BRAKE PADS
Generator Load Share Controller Governor CAT Woodward DSLC Synchronizer
Generator Load Share Controller Governor CAT Woodward DSLC Synchronizer
FREE 2 YR WARRANTY FREE US SHIPPING ON ORDERS OVER $100
FREE 2 YR WARRANTY FREE US SHIPPING ON ORDERS OVER $100
Euro Car Parts - The UK’s Largest Parts Distributor
Euro Car Parts - The UK’s Largest Parts Distributor
Euro Car Parts - The UK’s Largest Parts Distributor
ARMY ISSUE REFLECTIVE SET ~ HIGHWAY WARNING TRIAGLE ~ 9905-00-148-9544
ARMY ISSUE REFLECTIVE SET ~ HIGHWAY WARNING TRIAGLE ~ 9905-00-148-9544
9905-792 Woodward ProAct Governor Controller Model 9905-792 Used Tested Good
9905-792 Woodward ProAct Governor Controller Model 9905-792 Used Tested Good
9905-096 WOODWARD AUTOMATIC GENERATOR LOADING CONTROL--SA
9905-096 WOODWARD AUTOMATIC GENERATOR LOADING CONTROL--SA
9905-001 WOODWARD SPM-A SYNCHRONIZER--SA
9905-001 WOODWARD SPM-A SYNCHRONIZER--SA
8RA 002 016-121 HELLA Rear Reflector red
8RA 002 016-121 HELLA Rear Reflector red
{Brand New} Woodward 2301A Speed Control 9905-376
{Brand New} Woodward 2301A Speed Control 9905-376
Berger lahr WDPM3-314 WDPM3314 WDPM3-314.93210 SIG POSITEC
Berger Lahr WDPM3-314 WDPM3314 ALL TYPES AVAILABLE. WE SUPPLY ANY TYPE OF WDPM3
Berger Lahr SIG POSITEC WDPM3-314 REPAIR / WE FIX YOUR WDPM3 DRIVE
New Genuine WAI Starter Motor 17720R Top Quality 2yrs No Quibble Warranty
New Reliance Electric 812.53.00 D 24VDC Input Card
New Reliance Electric 812.56 Analog IN PCB Card 812.56.20
New Sealed Reliance Electric 812.53.00 D 24VDC Input Card
NEW, SIEMENS, RELIANCE ELECTRIC, 25-106-921-812, STARTERS & CONTACTORS. (6B-1)
Reliance 812.53.00BNS 24V DC PLC input module 812.53.00
Reliance 812.53.00D Card Input 8125300D 24 VDC
Reliance 812.53.00DUX Card Input 8125300DUX 24 VDC
Reliance 812.53.00DZW Card Input 24VDC 8125300DZW
Reliance 812.56.10FTZ Card 8125610FTZ
Reliance 812.5620FSX Card
Reliance 812.63.00DWW Card Output Contact
Reliance Electric 812.53.00 D 24VDC Input Card
Reliance Electric 812.53.00DTX Card Input 24 VDC 812.53.00
RELIANCE ELECTRIC 812.54.00 MERI INPUT 115 VAC MODULE
Reliance Electric 812.56. Analog IN Card 812.56.20.DQR
Reliance Electric 812.56.10CNN Analog Voltage Input Card 812.56.10
RELIANCE ELECTRIC 812.56.20 MERI ANALOG INPUT MODULE
Reliance Electric 812.6300DSx Card Output Contact 812.6300
reliance electric 812.68.00ayq
Reliance Electric Card Input 24 VDC 812.53.00DRX 812.53.00
Reliance Electric Electro Craft Servo Motor 6033-03-812
Reliance Electric Electro Craft Servo Motor 6033-03-812 w10:1
Reliance Electric Electro-Craft S-3016-N-H00AA Brushless Servo Motor 1 HP
Reliance Electric S-3007-N-H00AA Servo Motor Part# 6031-03-812 w/ Gearbox (CC4)
Reliance S61-E215-09 Input Board (Also shows part no. 812 660)
Zanussi ZOB1060X, ZOB660X, ZPB1260X Fan Oven COOKER ELEMENT 2000W 3 Turn
Zanussi ZOB1060X, ZOB660X, ZPB1260X Fan Oven COOKER ELEMENT 2000W 3 Turn
trutzschler ZPB3 9 495-12.430.000 AD 495-12.230.001 AE 495-12.230.002 AF CPU
