一般來說，PLC是極其可靠的設備，出故障率很低。PLC的CPU等硬件損壞或軟件運行出錯的概率幾乎為零；PLC輸入點如不是強電入侵所致，幾乎也不會損壞；PLC輸出繼電器的常開點，若不是外圍負載短路或設計不合理，負載電流超出額定范圍，觸點的壽命也很長。因此，我們查找電氣故障點，重點要放在PLC的外圍電氣元件上，不要總是懷疑PLC硬件或程序有問題，這對快速維修好故障設備、快速恢復生產(chǎn)是十分重要的，因此筆者所談的PLC控制回路的電氣故障檢修，重點不在PLC本身，而是PLC所控制回路中的外圍電氣元件。PLC系統(tǒng)接地要求比較嚴格，最好有獨立的專用接地系統(tǒng)，還要注意與PLC有關的其他設備也要可靠接地。多個電路接地點連接在一起時，會產(chǎn)生意想不到的電流，導致邏輯錯誤或損壞電路。 產(chǎn)生不同的接地電勢的原因，通常是由于接地點在物理區(qū)域上被分隔的太遠， 當相距很遠的設備被通信電纜或傳感器連接在一起的時候，電纜線和地之間的電流就會流經(jīng)整個電路，即使在很短的距離內(nèi)，大型設備的負載電流也可以在其與地電勢之間產(chǎn)生變化，或者通過電磁作用直接產(chǎn)生不可預知的電流。在不正確的接地點的電源之間，電路中有可能產(chǎn)生毀滅性的電流， 以至于破壞設備。工業(yè)現(xiàn)場的環(huán)境比較惡劣，存在著許多高低頻干擾。這些干擾一般是通過與現(xiàn)場設備相連的電纜引入PLC的。除了接地措施外，在電纜的設計選擇和敷設施工中，應注意采取一些抗干擾措施：

1、模擬量信號屬于小信號，極易受到外界干擾的影響，應選用雙層屏蔽電纜；

2、高速脈沖信號（如脈沖傳感器、計數(shù)碼盤等）應選用屏蔽電纜，既防止外來的干擾，也防止高速脈沖信號對低電平信號的干擾；

3、PLC之間的通信電纜頻率較高，一般應選用廠家提供的電纜，在要求不高的情況下，可以選用帶屏蔽的雙絞線電纜；

4、模擬信號線、直流信號線不能與交流信號線在同一線槽內(nèi)走線；

5、控制柜內(nèi)引入引出的屏蔽電纜必須接地，應不經(jīng)過接線端子直接與設備相連；

6、交流信號、直流信號和模擬信號不能共用一根電纜，動力電纜應與信號電纜分開敷設。

7、在現(xiàn)場維護時，解決干擾的方法有：對受干擾的線路采用屏蔽線纜，重新敷設；在程序中加入抗干擾濾波代碼。

SPI SPUTTER THIN FILM SPUTTERING DEPOSITION SYSTEM

GE PANAMETRICS ULTRASONIC LIQUID FLOWMETER DF868 DF 868

Crestron MPS-300 PROFESSIONAL MEDIA Control System

ALLEN BRADLEY 1785-L20E SERIES D 1785L20E ETHERNET

^ Topspin 120 24 Port Switch – CISCO

Akashi VEF Vacuum Evaporator

SORVALL ULTRACENTRIFUGE OTD65B CENTRIFUGE

HP 66000A MPS MAINFRAME – 66103A-66101A-6?6106A-16A MODS

Canon BJ-W9000 wide format Printer w/ IMAGEPASS W20

*NUAIRE NU 430 600 CLASS II B2 BIOLOGICAL FUME HOOD

GRAPHTEC CS2000 LARGE FORMAT SCANNER

FINISH THOMPSON LITTLE STILL SOLVENT RECOVERY UNIT LSJR

HOLLYWOOD POP POPCORN VENDING MACHINE HF-150

GERSTEL GS1 GS 1 GAS SAMPLER

CRESTRON QM-MD7X2 VIDEO MATRIX SWITCHER AUDIO PROCESSOR

FEDERAL FORMSCAN 3000 CIRCULAR GEOMETRY GAGE

HIGHLITE 4000SX DLP PROJECTORS – wow! -b

~ LEYBOLD TURBOVAC 150 TURBO PUMP

^LOT OF SIX APPLE G4 POWERMACS- 733mhz, 533mhz, 433mhz

~ LOT OF 75+ APPLE M7803 BLACK AND WHITE KEYBOARDS-

LOWEL TOTA LIGHTING UNITS- STANDS -CASE

SEM 200 HIGH SECURITY SHREDDER

HP 3314A FUNCTION GEN & 5342A MICROWAVE FREQ COUNTER

MTS TESTSTAR CONTROLLER

SIX X-RAY FILM ILLUMINATOR 4 BANK UNITS- 56X17

* LITTON VERTICAL SEAL MACHINE MODEL D

STEINBICHLER COMET 100 HEAD- 3D DIGITIZING ??

IMETRIC ISCAN ? 3D SCANNING ACCESSORIES IN CASES

ENCAD NOVAJET 850 6ft WIDE FORMAT PRINTER/PLOTTER

EPSON STYLUS PRO 9600 4FT WIDE FORMAT PRINTER/PLOTTER

CASTLE DUAL L-195 ADJUSTABLE SURGICAL LIGHT

HASKEL Air Driven Fluid Pump DSHF-300 50,000 PSI

EG&G ORTEC 92X SPECTRUM MASTER

THREE LOWEL SOFTLIGHT 1500 LIGHTING SYSTEM

COSA 6000 CD PORTABLE STACK EMISSION ANALYSER

DI DIGITAL INSTRUMENTS PICOFORCE SPECTROSCOPY CONTROL

* ASSOCIATED ENVIROMENTAL CHAMBER BD-101-S3C
RAMSCO SD-60-IRC CHAMBER

EXTRON MAV 1616 SERIES SWITCHER

Master-Bilt (GT-40) 49″ Horizontal Display Freezer

UNION CARBIDE LR-30A Cryo Tank Liquid Nitrogen Dewar

SPECTRA LOGIC SPECTRA 10000 TAPE DRIVE

OXFORD PROJECT NR 38015 5FT DETECTOR? SETUP?

HAMILTON BEACH 990 COMMERCIAL HEAVY DUTY FOOD BLENDER

SPECTRACE 9100-4203 X-RAY XRF SPECTROMETER controller?

FACIT TAPE PUNCH READER MODEL 4047

TEKTRONIX 7S12 TDR/SAMPLER W/S-6 / S-52 HEAD PLUG IN

NEWPORT MOTION CONTROLLER MM3000

Extron Matrix 6400 Sync Switch

~ NVIDIA MAC GEFORCE GTX 285 GRAPHICS CARD

^ Pacific-Atlanti?c PT-55 HV Pulse/trigger Generator

AMERICAN SURGICAL C22T51 19″ ADJUSTABE SURGICAL LIGHT

SEM 200 HIGH SECURITY SHREDDER

HP 3314A FUNCTION GEN & 5342A MICROWAVE FREQ COUNTER

MTS TESTSTAR CONTROLLER

SIX X-RAY FILM ILLUMINATOR 4 BANK UNITS- 56X17

* LITTON VERTICAL SEAL MACHINE MODEL D

STEINBICHLER COMET 100 HEAD- 3D DIGITIZING ??

IMETRIC ISCAN ? 3D SCANNING ACCESSORIES IN CASES

ENCAD NOVAJET 850 6ft WIDE FORMAT PRINTER/PLOTTER

EPSON STYLUS PRO 9600 4FT WIDE FORMAT PRINTER/PLOTTER

CASTLE DUAL L-195 ADJUSTABLE SURGICAL LIGHT

HASKEL Air Driven Fluid Pump DSHF-300 50,000 PSI

EG&G ORTEC 92X SPECTRUM MASTER

THREE LOWEL SOFTLIGHT 1500 LIGHTING SYSTEM

COSA 6000 CD PORTABLE STACK EMISSION ANALYSER

DI DIGITAL INSTRUMENTS PICOFORCE SPECTROSCOPY CONTROL

* ASSOCIATED ENVIROMENTAL CHAMBER BD-101-S3C
RAMSCO SD-60-IRC CHAMBER

EXTRON MAV 1616 SERIES SWITCHER

Master-Bilt (GT-40) 49″ Horizontal Display Freezer

UNION CARBIDE LR-30A Cryo Tank Liquid Nitrogen Dewar

SPECTRA LOGIC SPECTRA 10000 TAPE DRIVE

OXFORD PROJECT NR 38015 5FT DETECTOR? SETUP?

HAMILTON BEACH 990 COMMERCIAL HEAVY DUTY FOOD BLENDER

SPECTRACE 9100-4203 X-RAY XRF SPECTROMETER controller?

FACIT TAPE PUNCH READER MODEL 4047

TEKTRONIX 7S12 TDR/SAMPLER W/S-6 / S-52 HEAD PLUG IN

NEWPORT MOTION CONTROLLER MM3000

Extron Matrix 6400 Sync Switch

~ NVIDIA MAC GEFORCE GTX 285 GRAPHICS CARD

^ Pacific-Atlanti?c PT-55 HV Pulse/trigger Generator

AMERICAN SURGICAL C22T51 19″ ADJUSTABE SURGICAL LIGHT

Standard Register Image Seal 608

PERKIN ELMER 8410 CAPILLARY GAS CHROMATOGRAPH

* 15+ BESELER EG&G NEGATIVE CARRIERS

LEO WAFER T LTA-130A SYSTEM

BARRACUDA NETWORKS SPAM & VIRUS FIREWALL 300

BUNN SINGLE B SATELLITE BREWER SERVER COFFEE MAKER

XEROX 6250 TONER SET- BLACK-CYAN-MAGE?NTA-YELLOW

TEKTRONIX PROGRAMMABLE PULSE HEAD 015-0611-00 / CG5011

BRADY TLS2200 THERMAL LABELING SYSTEM

HP 5342A MICROWAVE FREQUENCY COUNTER OPT/011

FLEETWOOD CORDLESS WIRELESS AUDIENCE RESPONSE KEYPADS

* 50+ LISCO & FIDELITY 4×5 & 21/4x 31/4 FILM CASSETTES

WALLACE GUARDIAN 1414 LIQUID SCINTILLATION UNIT

CETAC ULTRASONIC NEBULIZER U-5000AT

Bio-Tek Precision 2000 Microplate Pipetting System

FLUKE VOLTAGE CALIBRATOR MODEL 313A

TEKTRONIX 067-0616-00 CALIBRATION FIXTURE EXTENDER

HP Agilent 66001A MPS Keyboard for HP/Agilent 66000A

HP AGILENT 5385A FREQUENCY METER

* UNITED POWER PDM2-F3-125-426 PDU POWER DISTRIBUTION

LECROY 1434A CAMAC CRATE- 6880A WAVEFORM – 6010 MAGIC-d

LECROY 1434A CAMAC CRATE-6103, tr8828c, mm8104,8901a- b

~ YORK F-BK2 THOMAS/BETTS OPTICAL FIBER CLEAVING TOOL

CADCO UNOX OV-400 XA030 CONVECTION OVEN

~TITMUS 2a VISION TESTER W/ SLIDES- MISSING LID-a

*MRF FURNACE CONTROL- HOYT – HONEYWELL- GATTERING

RUSKA DDR 6000 DIRECT READING PRESSURE GAGE

ENDEVCO CCAS COMPUTER SIGNAL CONDITIONER W/CARDS

~ BROWN & SHARPE HANDHELD XYZ CONTROLLER

~ IRD MECHANALYSIS MODEL 306 VIBRATION METER

專業(yè)銷售進口DCS? PLC系統(tǒng)備件模塊