PLC是以微處理器為基礎，綜合了計算機技術、自動控制技術和通信技術，用面向控制過程面向用戶的“自然語言”編程，適應工業(yè)環(huán)境，簡單易懂、操作方便、可靠性高的新一代通用工業(yè)控制裝置。PLC是在繼電器順序控制基礎上發(fā)展起來的以微處理器為核心的通用自動控制裝置。

可編程序控制器是一種數(shù)字運算操作電子系統(tǒng)，專為在工業(yè)環(huán)境下應用而設計。它采用了可編程序的存儲器，用來在其內(nèi)部存儲執(zhí)行邏輯運算、順序控制、定時、計數(shù)和算術運算等操作指令，并通過數(shù)字的、模擬的輸入和輸出，控制各種類型的機械或生產(chǎn)過程?？删幊绦蚩刂破骷捌溆嘘P的外圍設備，都應按易于與工業(yè)控制系統(tǒng)形成一個整體、易于擴充其功能的原則設計。

PLC產(chǎn)品種類繁多，其規(guī)格和性能也各不相同。對于PLC，通常根據(jù)其結構形式的不同、功能的差異和I/O點數(shù)的多少等進行大致分類。

按結構形式分類

根據(jù)PLC的結構形式，可將PLC分為整體式和模塊式兩類。

整體式PLC

整體式PLC是將電源、CPU、I/O接口等部件都集中裝在一個機箱內(nèi)，如圖所示。具有結構緊湊、體積小、價格低的特點。小型PLC一般采用這種整體式結構。整體式PLC由不同I/O點數(shù)的基本單元（又稱主機）和擴展單元組成，基本單元內(nèi)有CPU、I/O接口、與I/O擴展單元相連的擴展口以及與編程器或EPROM寫入器相連的接口等；擴展單元內(nèi)只有I/O和電源等，而沒有CPU?；締卧蛿U展單元之間一般用扁平電纜連接。整體式PLC一般還可配備特殊功能單元，如模擬量單元、位置控制單元等，使其功能得以擴展。

2）模塊式PLC

模塊式PLC將PLC的各組成部分分別做成若干個單獨的模塊，如CPU模塊、I/O模塊、電源模塊（有的含在CPU模塊中）以及各種功能模塊。模塊式PLC由框架或基板和各種模塊組成，模塊裝在框架或基板的插座上，如圖所示。這種模塊式PLC的特點是配置靈活，可根據(jù)需要選配不同規(guī)模的系統(tǒng)，而且裝配方便，便于擴展和維修。大、中型PLC一般采用模塊式結構。

還有一些PLC將整體式和模塊式的特點結合起來，構成所謂的疊裝式PLC。疊裝式PLC的CPU、電源、I/O接口等也是各自獨立的模塊，但它們之間是靠電纜進行連接的，并且各模塊可以一層層地疊裝。這樣，不但系統(tǒng)可以靈活配置，還可做得體積小巧。

2.2.按功能分類

根據(jù)PLC的功能不同，可將PLC分為低檔、中檔、。

SUPERIOR PRODUCTS 3.5" long, 1/4" NP7 CHROME INLET NIPPLE
*     * SUPERIOR ELECTRIC SLO-SYN SYNCHRONOUS / STEPPING MOTOR SS25-1140
*     * Superior Tool 1/8" to 1-1/8" Mini Tube Cutter 35180
~ *       * ~ KOHSHIN Superior noise-resistance ~ HC-PG050V4B15 ~
~Superior Ball Valve 7/8"x1'' ODS--     --NR~~
~Superior Check Valve-- Brass 3/4" OD--5/8''ID Solder----       ~
~Superior Packed Angle Valve 600B-4U4 -- ODS 1/4''--      ~
1 1/4" ~ Superior Valve Wrench
1       Steel Solid Bolt 5/8" -11 x 1-1/2" Long
1       Steel Solid Caster Axle 3/4" -10 x 3 7/16" Long with Nut (No Grease Zerk)
1       Steel Solid Caster Axle 5/8" -11 x 3-7/8" Long with Nut (No Grease Zerk)
1       Steel Solid Caster Axle 5/8" -11 x 3-7/8" Long with Nut (No Grease Zerk)
1       SUPERIOR PRODUCTS, INC. CGA-540 REGULATOR INLET NUT FOR OXYGEN
1 pair (2pcs) of Jantzen Superior Z-Cap MKP Capacitors 2% 800-1200V (all values)
1 Pair, 14" SUPERIOR QUALITY LEATHER WELDING GLOVES
1 Pcs Iris Dental Surgical Scissor Premium Quality, Superior Cutting, Reusable
1 PK! OLIVETTI STUDIO 44 TYPEWRITER RIBBON We Offer Superior Quality For Less!
1 SUPERIOR OR GE BALLAST 8G1532WF      
1 SUPERIOR SG350 WIRE CABLE CONNECTOR BRASS 250 350 MCM 3/8-16 BOLTS 2" X 1-1/8"
1 X 1 24 GRIT SUPERIOR ABR SPIRAL BANDS (AA523-34)
1 X 1 24 GRIT SUPERIOR SPIRAL BANDS (AA522-26)
1" - 8 UNC taper Pipe Die 1-8 UNC Superior quality (1PCS)
1" - 8 UNC taper Pipe Die 1-8 UNC Superior quality (1PCS)
1/2 - 24 UNF HSS Right Hand Thread Tap 1/2 - 24 TPI Superior quality (1PCS)
1/2" internal pipe wrench Superior Tool FREE SHIPPING!
1/4" NPT Superior Quality T Serise Nylon Tubing Pneumatic Tube Connector Fitting
1/4-18 NPT pipe tap High Carbon Steel, Brand      , 1/4 pipe tap Superior quality
1/6" NPT Male Pneumatic Exhaust Mufflers of Superior Quality
1/8 To 1-1/4 Tubing Cutter SUPERIOR TOOL Tube Cutters 35219 017197352195
1/8 To 1-1/8 Mini Tube Cutter Superior Tool Tube Cutters 35180 017197751806
1/8 To 1-1/8 Tubing Cutter Superior Tool Tube Cutters 35275 017197352751
1/8 To 7/8 Mini Tube Cutter Superior Tool Tube Cutters 35078 017197350788
1/8-27 NPT pipe tap, High Carbon Steel, Brand      , 1/8 pipe tap Superior quality
1/8X5/8 Mini Tubing Cutter Superior Tool Tube Cutters 35025 017197350252
1:1/2:1 Dental Impression Mix Dispenser Dispensing Caulking Gun 50ml superior #o
10 for 10 Black Binding Posts solid brass Superior Electric BP30 30amp
10 Pairs All –purpose Superior Gloves Working String Knit Latex Dipped Firm Grip
10 Pcs Alloy CNC Carbide Micro Drill Bits 1.1mm-2.0mm Superior Grinding Process
10 Pcs Practical Superior 2x40 Pin 2.54mm Pitch Double Row PCB Pin Headers DI
10 Pcs Practical Superior 2x40 Pin 2.54mm Pitch Double Row PCB Pin Headers WD
10" x 2-3/4" Pneumatic Tires Durable Superior Load 650lbs Hand Truck Wheel
100 #3 (Poly) Superior Quality Bubble Mailers 8.5x14.5
100 piece box of Superior 2 1/4" Rebar Chairs $ 28.50
104' Superior Essex Cat 3 UTP 2-Pair Grey
10pcs APMT1604PDER-H2 LF6018 Superior quality Milling cutter blade carbide
10pcs APMT1604PDER-M2 LF6018 Superior quality Milling cutter blade carbide
10Pcs Practical Superior 2x40 Pin 2.54mm Pitch Double Row PCB Pin Headers LWSZUS
10pcs RDMT1204MO-MQ LF6028 Superior quality Milling cutter blade carbide
10pcs RPMT1003-M0-TT LF6028 Superior quality Milling cutter blade carbide
10pcs/lot VISHAY DALE 0.5W 4.42k Superior resistance
10pcs/lot welwyn W21 3W 1R2 1.2R Superior resistance Behalf 3W 1R
11 SUPERIOR TOOL HEX ALLEN L-WRENCH KEY SET 3/8" TO .050" EXCELLENT CONDITION
1-1/2" Lathe Collet Pads out of box Superior Cincinnati 1025-200-2125 USA
1-1/2" Tightspot Wrench Superior Tool Wrenches 03915 017197039157
1-1/8 Od Hvyduty Tubing Cutter Superior Tool Tube Cutters 35236 017197752476
12 Inch Lazy Susan
12       SUPERIOR #GNT-(10 XL) Nitrex Nitrile Coated Palm Gloves cut-resistant
12 PAIR XLARGE SUPERIOR TOUCH S18PU-10 POLYURETHENE LIGHT DUTY WORK GLOVES
12 SUPERIOR SLIDE LOCK DIES MOLDS 8lb SLK-8A 25 SLK-25A
12 WINDSOR MEDIUM WEIGHT DINNER KNIVES 8" Superior Apn 2699528
12" Lab-Flex® 160 up to 37+ GHz 3.5 mm low loss superior shielded RF cable       
13" Lab-Flex® 160 up to 37+ GHz 3.5 mm low loss superior shielded RF cable       
13In Complete PVC Saw Superior Tool Pvc Cutters 37513 017197775130
141117 Old-Stock, Superior Tire 535 STD Poly Wheel, 2" ID, 3" OD
17" Lab-Flex® 160 up to 37+ GHz 3.5 mm low loss superior shielded RF cable       
18 SUPERIOR #1 6'' COPPER ELECTRICAL WATER PIPE GROUNDING STRAP
1947 ROCK - IT CORN GRADER OPERATING INSTRUCTIONS service manual SUPERIOR USA
1954 GENOMETER- operating manual for TV 50- superior instruments, factory issue
1959.caterpillar tractor superior lubricants series 3 oil change for cat diesel
1960 Operating Instructions For Model TW-11 Tube Tester
1pc       HSS Left Machine Tap 1" -14 Tap Threading Tools 1" -14 Superior quality
1PCS C8051F530A Superior perbance to emulation systems SSOP20
1pcs HSS Right Hand Die 3/4"-10UNC Dies Threading 3/4-10UNC Superior qualit
1pcs HSS Right Hand Tap 1/2"-27 NS Taps Threading 1/2-27 NS Superior quality
1pcs HSS Right Hand Tap 1/2"-32UN Taps Threading 1/2-32UN Superior quality
1pcs HSS Right Hand Tap 3/8"-16UNC Taps Threading 3/8-16UNC Superior quality
1pcs HSS Right Hand Tap 7/16"-28UNEF Taps Threading 7/16-28UNEF Superior quality
1pcs        41×16.5×30 400v2.7uf 275 fever Superior film Capacitors