140XBP00400

如果我们所开发的设备并不是像航空航天器那样生命攸关或者生产控制那样的关键任务系统，而是像消费电子类那样，即使出现错误也不会造成灾难后果的设备，那么实时（严格地讲是确定）是否还具有现实意义呢？答案是肯定的！设备的高可靠可以有效地降低维护成本；软件运行效率高也会降低对的要求，从而降低硬件成本。对于消费电子产品这类价格十分敏感的产品，实时、可靠仍然是值得重视的问题。

 

坚如磐石――可靠

 

桌面操作系统与RTOS相比，另一个差别就是对于稳定、可靠方面的设计思路。一方面，桌面操作系统比较庞大、复杂，而RTOS比较小巧、简捷，而“越简单、越可靠，越复杂、故障概率越大”这又是一个常理。另一方面，更重要的是：桌面操作环境与嵌入式环境在设计思路上有一个重大的不同——桌面环境假定应用软件与操作系统相比而言可以是不可靠的，而嵌入式环境假定应用软件与操作系统一样可靠。

 

运行于嵌入式环境中的RTOS要求应用软件具有与操作系统同样的可靠，这种设计思路对应用开发人员提出了更高的要求，同时也要求操作系统自身足够开放。
的“木桶原理”告诉我们，局部的不足会导致整体的缺陷。要保证系统的可靠，必须保证系统中每一个部分都是可靠的，任何部分的不可靠都会导致系统整体的不可靠。大多数桌面系统都是上千万行代码的庞大而复杂的系统，即使有源代码程序员也难以把握。而且对开发人员来说，桌面系统庞杂的细节是隐蔽在一个个的固定的接口下的，是一个黑箱，很难把握具体执行的线索。即便其内核是足够可靠的，但它的应用环境复杂多样、千差万别，其中常常有一些应用并不是那么稳定可靠，从而破坏了整体系统的可靠。相反，RTOS对软件开发人员来说是完全开放的，是一个白箱，允许开发人员清楚地了解和掌握操作系统内部情况，对存储器中的每一位和每一个I/O接口进行操作控制，从而可以设计出高效稳定的应用软件。

 

可编程控制器（PROGRAMMABLE CONTROLLER，简称PC）。与个人计算机的PC相区别，用PLC表示。

 

PLC是在传统的顺序控制器的基础上引入了微电子技术、计算机技术、自动控制技术和通讯技术而形成的一代新型工业控制装置，目的是用来取代继电器、执行逻辑、记时、计数等顺序控制功能，建立柔的程控系统。国际电工委员会（IEC）颁布了对PLC的规定：可编程控制器是一种数字运算操作的电子系统，专为在工业环境下应用而设计。它采用可编程序的存贮器，用来在其内部存贮执行逻辑运算、顺序控制、定时、计数和算术运算等操作的指令，并通过数字的、模拟的输入和输出，控制各种类型的机械或生产过程。可编程序控制器及其有关设备，都应按易于与工业控制系统形成一个整体，易于扩充其功能的原则设计。

 

PLC具有通用强、使用方便、适应面广、可靠高、抗干扰能力强、编程简单等特点。可以预料：在工业控制领域中，PLC控制技术的应用必将形成世界潮流

 

PLC程序既有生产厂家的系统程序，又有用户自己开发的应用程序，系统程序提供运行平台，同时，还为PLC程序可靠运行及信息与信息转换进行必要的公共处理。用户程序由用户按控制要求设计。

 

一般讲，PLC分为箱体式和模块式两种。但它们的组成是相同的，对箱体式PLC，有一块板、I/O板、显示面板、内存块、电源等，当然按能分成若干型号，并按I/O点数又有若干规格。对模块式PLC，有模块、I/O模块、内存、电源模块、底板或机架。无任哪种结构类型的PLC，都属于总线式开放型结构，其I/O能力可按用户需要进行扩展与组合。PLC的基本结构框图如下：

 

 

36A358204AA001 CARD FRAME RETAINING
36A358207AAG01 R/C NETWORK
36A358207AAG03 R/C NETWORK 5″ W/SPA
36A358208AAG01 5PL CABLE
36A358208AAG02 1PL CABLE
36A358208AAG04 3PL CABLE
36A358208AAG05 WIRE BUNDLE 7PL CABL
36A358208AAG06 8PL CABLE
36A358208AAG07 4PL CABLE
36A358208AAG08 WIRE BUNDLE 6PL CABL
36A358208AAG09 10PL 3 CABLE C & G FRA
36A358208AAG10 12PL CABLE
36A358208AAG11 11PL CABLE C & G FRAME
36A358208AAG12 13PL CABLE C & G FRAME
36A358208AAG14 17PL CABLE
36A358208AAG18 PROGRAMMER CABLE (6′
36A358208AAG19 PROGRAMMER CABLE (8′
36A358208ABG01 8PL 10 CABLE
36A358208ACG01 WIRE BUNDLE
36A358208ADG01 18 PL CABLE
36A358208ARG01 PROGRAMMER CABLE (10
36A358208CCG06 6PL R6 CABLE ASM
36A358208CEG07 CABLE ASM
36A358208CXG01 9PL RIBBON CABLE
36A358208ERG04 PCOM PX CABLE (DC300
36A358208EYG01 14PL M C & G FRAME
36A358208EYG02 14 PL M CABLE (DC600
36A358216AA001 OVERLAY
36A358218BCG02 GATE LEADS R REG W B
36A358218BRG01 AC FUSE MA WIRE BUNDLE
36A358218FXG01 CABLE
36A358218FXG02 CARD PPL CABLE
36A358218RBG01 WIRE HARNESS
36A358218XAG01 4PL CABLE
36A358218XAG02 6PL CABLE
36A358218XAG03 10PL CABLE
36A358218XAG04 11PL D FRAME
36A358218XAG05 12 PL CABLE
36A358218XAG06 13PL D FRAME
36A358218XAG07 WIRE HARNESS
36A358218YAG02 CT ASM (2)
36A358241AAG01 MOV ASM
36A358250AC001 LATCH
36A358250AC002 LATCH
36A358256AAG01 CAPACITOR ASM
36A358260CX001 GASKET
36A358941AAG02 MAINTENANCE KIT DC2000 JU
36A359100CDG02 29PLM CABLE LAN DC D
36A359100CDG04 29PL MICRO APPL CARD
36A359100CRG01 RPL CABLE
36A359100CRG02 RPL CABLE
36A359100CRG03 PANEL RPLDC E
36A359100CYG13 OPTPL JUMPER
36A359100CYG14 LTB/3TB 115V FEED CARD
36A359100CYG15 LTB/3TB 115V FEED CARD
36A359102AAG01 SCR ASM
36A359102AAG03 SCR ASM
36A359102AAG04 SCR AND CONNECTOR
36A359113AC001 2″ SPACER
36A359113AC002 4″ SPACER
36A359113AC003 6″ SPACER
36A359126AEG01 CABLE
36A359133AAG01 LAN POWER SUPPLY
36A359141ABG03 5PL IOS (20″) CABLE
36A359141ACG01 3PL RIBBON (IOS)
36A362260AA003 DC TRANSMITTER
36A362260AA012 TRANSDUCER
36A362432DA001 CURRENT IND METER
36A362535BD004ｍａｓｔｅｒSWITCH
36A362535BD006ｍａｓｔｅｒSWITCH
36A362717CE002 METER 20-0-20A DO91
36A362717CF003 AMMETER
36A362717CF012 AMMETER
36B605201AAG03 SCR W/ TERMINALS
36B605201AAG07 SCR W/ TERMINALS
36B605201ABG01 SCR W/ TERMINALS
36B605224EAG01 SNUBBER ASM
36B605308FBG01 KIT CB J600
36B605519BA001 CARD DOOR (2000)
36B605538AAG01 TRANSFORMER ASM
36B605538AAG02 TRANSFORMER ASM
36B605538ABG01 TRANSFORMER ASM
36B605538ABG02 TRANSFORMER ASM
36B605538ACG02 CONT POWER TRANSFORMER
36B605538AEG02 CPT ASM (460V)
36B605543AC001 SHEETMETAL ASM
36B605548AAG01 PROGRAMMER CARD ASM
36B605553AAG04 3 POS POWER BLOCK W/BARR
36B605553AAG05 1 POS POWER BLOCK W/BARR
36B605573AAG01 TRANSFORMER ASM
36B605573ACG01 TRANSFORMER ASM
36B605573AEG01 TRANSFORMER ASM
36B605573AYG01 CONTROL TRANSFORMER C EX
36B605573BEG01 CPT ASM 4 6A
36B605573BEG02 CPT ASM 575V 4 6A 11
36B605573BFG01 CPT ASM 3 0A
36B605575AD002 4Q SCR BUS ‘G’
36B605575AE001 INSULATION
36B605593AAG04 FAN MOTOR
36B605594AAG01 BALUN ASM
36B605594ABG01 ENC/DIG TACH BALUN A
36B605594AEG01 ARCNET I/F CARD MOUNTING
36B605609BX002 PLENUM COVER
36B605611AE001 BUS BAR 1/8X2
36B605612AA001 HEATSINK LONG
36B605612AB001 SHORT HEATSINK
36B605619AAG02 BRAIDED CABLE
36B605619AAG03 BRAIDED CABLE
36B605619AAG04 BRAIDED CABLE
36B605619ABG06 P1A CABLE ‘C’ EXT (2)
36B605619ABG07 P2 CABLE ‘C’ EXT (2)
36B605619ACG01 CABLE ASM
36B605619ACG03 BRAIDED CABLE
36B605619ACG06 BRAIDED CABLE
36B605619ADG01 CABLE ASM
36B605625BAG01 APL SHUNT TRANS WIRE ASM
36B605625BAG02 BPL SHUNT TRANS WIRE ASM
36B605625BAG03 CPL SHUNT TRANS WIRE ASM
36B605633AAG01 CT ASM
36B605731AC001 4Q SCR BUS ‘G’
36B605756ABG01 POTTED MOV ASM
36B605756ABG02 MOV ASM 575V
36B605756ADG01 DC300 POWER SUPPLY K
36B605776AAG02 CONTROL TRANSFORMER
36B605787AAG01 HARNESS DC2000
36B605787AAG02 2PL CABLE “DC DX”
36B605787AAG03 2PL CABLE ASM
36B605787AAG05 2PL CABLE
36B605787AAG06 2PL CABLE
36B605787AAG07 2PL CABLE
36B605787ACG01 2PL W/ ARCNET G
36B605787ACG02 2PL W/ ARCNET ‘D’
36B605787ACG03 2PL W/ ARCNET ‘P’
36B605787ACG04 2PL W/ ARCNET ‘Q’
36B605787ACG05 2PL W/ ARCNET
36B605787ACG06 2PL CABLE W/ LCC CARD
36B605787ACG08 2PL IMCP 3TB LDCC AD
36B605796AAG01 USE 36B605796AAG101
36B605796AAG09 ARCNET DCPL IOS (26″)
36B605796AAG101 ARC PL CABLE G
36B605796AAG102 ARC PL CABLE G
36B605796AAG118 ARC PL CABLE G
36B605796AAG18 ARC PL CABLE D
36B605796AAG19 CABLE DLAN ASM
36B605796AAG22 ARC PL CABLE D
36C774122AFG01 SUPPORT MOTOR HOUSING
36C774122BAG01 MOTOR BRACKET AC500
36C774122BAG02 MOTOR BRACKET
36C774122CCG01 SUPPORT MOTOR HOUSING C F
36C774282AAG01 MOVABLE RELAY ASM
36C774296CCG01 DOOR
36C774298EAG12 FILTER SUPPORT & FILTER 14X
36C774298ECG12 FILTER SUPPORT & FILTER 20X
36C774298EDG12 FILTER SUPPORT & 20X25X1
36C774300AA001 CARD FRAME
36C774300BA001 DC2000 KEYPAD SUPPORT
36C774302AAG07 TERMINAL BLOCK 1 POI
36C774344ABG01 POWER SUPPLY ASM
36C774345AAG01 MFC ASM
36C774345BAG01 ASM MFC REMOTE W/GAS
36C774353AAG01 STACK ASM
36C774353AAG06 STACK 1QL 153 W/FERRITES
36C774353ABG09 STACK 1QR 123 G2SNUB
36C774353ADG05 STACK 4QL 152 ASM
36C774353ADG06 STACK 4QL 154
36C774353AEG11 STACK ASM
36C774353AEG12 STACK ASM
36C774360ACG01 DB RESISTOR KIT
36C774360BEG01 DB RESISTOR KIT
36C774374AFG01 POWER LINE MONITOR ASM
36C774507ABG01 TACHOMETER ISOLATOR
36C774524AAG05 11PL RIBBON CABLE
36C774524AAG08 13PL RIBBON CABLE
36C774524AAG200 8PL CABLE
36C774524AAG201 8PL CABLE W/ NTBA
36C774524AAG202 8PL CABLE
36C774524AAG203 8PL
36C774524AAG204 8PL CABLE W/ LTB
36C774524AAG205 8PL LDCC 3TB/STBA LT
36C774524AAG206 8PL CABLE
36C774524AAG31 10PL RIBBON CABLE
36C774524AAG34 14PL RIBBON CABLE
36C774524AAG35 CABLE 1 PL “DC GX”
36C774524AAG36 3PL CABLE
36C774524AAG37 4PL CABLE
36C774524AAG38 5PL CABLE “DC GX”
36C774524AAG39 6PL CABLE “DC GX”
36C774524AAG41 8PL CABLE “X”
36C774524AAG43 1OPL CABLE “DC GX”
36C774524AAG44 8PL CABLE “DC
36C774524AAG45 4PL CABLE “DC DX”
36C774524AAG46 6PL CABLE “DC DX”
36C774524AAG47 IOPL DC DX
36C774524AAG48 1PL RIBBON CABLE
36C774524AAG49 4PL RIBBON CABLE
36C774524AAG50 BDCPL CABLE AC PX
36C774524AAG51 7PL CABLE “DC
36C774524AAG60 1PL CABLE ASM
36C774524AAG61 4PL CABLE ASM
36C774524AAG62 CABLE 1PL
36C774524AAG63 4PL CABLE ASM
36C774524AAG64 6PL CABLE “FCR”
36C774524AAG66 IOPL FCR
36C774524AAG67 5PL FCRR
36C774524AAG68 1PL CABLE
36C774524AAG69 IOPL
36C774524AAG70 6PL CABLE ASM
36C774524AAG71 1PL CABLE ASM
36C774524AAG72 1PLX CABLE ASM
36C774524AAG73 GSPL CABLE ASM
36C774524AAG87 IOPL “RC
36C774524AAG88 IOPL LDCC RTB
36C774524AAG90 6PL SDCC/LDCC 3TB/ST
36C774524AAG91 1PL CABLE “D
36C774524AAG93 1PL CABLE
36C774524AAG94 1PL CABLE
36C774524AAG95 1PL CABLE ASM
36C774528BB001 BACKPLATE G TOPHAT
36C774545AAG03 DB CONTACTOR ASM 40
3805671G2 CONTACT TIP FOR IC1050
3814040P1 YOKE
3814065P1 LEVER
3814070G1 BOX
3814070P2 BACK
382A1450P0001 AERO ENERGY EX2100
385X112G1PM NEUTRAL GROUND RESISTOR :240V 104A CONTIN
385X116G1PM IC9133Y RESISTOR 2 OF 9033C3C1
385X116G7PM IC9133Y RESISTOR 2 OF 9033C3C1
385X123G3PM RESISTOR ASM 0 038 OHMS 192 AMPS
3860817G1 BRAKE SHOE W/LINING
3860820XXPX 3 22″ NO BORE BRAKE WHEEL
3860820YSP3 WHEEL
3860823BEP109 8″ STR BORE WHEEL 9516463 BRAKE
3860823FFP7 8″ WHEEL
3860825HHP7 14″ BRAKE WHEEL
3860826XXPX 19” STD BLANK BORE WHEEL
3860962G2 CONTACT TIP >
3865674G1 SUPPORT
3866756G2 TIP MOVABLE 2800Y108 1180
3897180P4 PLATE
3897180P7 PLATE
3897181G1 TORQUE ROD AND CROSS HEAD
3897181P4 CROSS HEAD
3897181P6 ADJUSTING NUT
3897182P12 BACK STOP ANGLE
3897182P4 TIE ROD
3897183P2 SPRING SEAT
393B103G2 COIL
393B103G3 COIL
393B162G2 COIL FOR IC2820
393B162G4 COIL XXX VDC >IC2800Y106
393B162G5 COIL
393B200G17 COIL
393B200G20 COIL
393B200G21 COIL
393B200G23 COIL
393B200G5 COIL
393B200G6 COIL 440V AC 60HZ >
393B202G11 COIL
393B202G16 COIL
393B202G17 COIL >IC2812B207
393B202G18 COIL
393B202G2 COIL
393B202G20 COIL
393B202G21 COIL
393B202G22 COIL
393B202G29 COIL
393B202G3 COIL
393B202G32 COIL
393B202G4 COIL
393B202G43 COIL
393B202G7 COIL
393B202G8 COIL
393B203G10 COIL
393B203G12 COIL
393B203G19 COIL XXX VDC >IC2820E500
393B203G21 COIL
393B203G9 COIL
393B209G3 USE 1D106G3A
393B216G5 COIL >IC3605
393B425G2 SHUNT
394B522P7 CONNECTOR STRIP >28001612CU CONTACTOR