IC646PPD364，IC646PPD364，IC646PPD364
可編程控制器的掃描周期及工作過程
可編程控制器的工作過程包括兩部分：自診斷及通信響應的固定過程和用戶程序執行過程，如圖1所示。PLC在每次執行用戶程序之前，都先執行故障自診斷程序、復位、監視、定時等內部固定程序，若自診斷正常，繼續向下掃描，然后PLC檢查是否有與編程器、計算機等的通信請求。如果有與計算機等的通信請求，則進行相應處理。當PLC處于停止（STOP）狀態時，只循環進行前兩個過程。而在PLC處于運行（RUN）狀態時，PLC從內部處理、通信操作、輸入掃描、執行用戶程序、輸出刷新五個工作階段循環工作。每完成一次以上五個階段所需要的時間稱為一個掃描周期。
掃描周期是PLC的一個重要指標，小型PLC的掃描周期一般為十幾毫秒到幾十毫秒。PLC的掃描周期長短取決于掃描速度和用戶程序的長短。毫秒級的掃描時間對于一般工業設備通常是允許的，PLC對輸入的短暫滯后也是允許的。但對某些I/O快速響應的設備，則應采取相應的處理措施。如選擇高速CPU，提高掃描速度；選擇快速響應模塊、高速計數模塊以及不同的中斷處理等措施減少滯后時間。對于用戶來說，要提高編程能力，盡可能優化程序；而在編寫大型設備的控制程序時，盡量減少程序長度，選擇分支或跳步程序等，都可以減少用戶程序執行時間。
ALLEN-BRADLEY 872C-A10N30-R3 N.O. SN:10mm 20-250VAC PROXIMITY SWITCH
ALLEN-BRADLEY 871TM-DH5NP18-N4 DC PROXIMITY SENSOR 5MM SN PNP - ! QUANTITY!
Allen-Bradley 871TM-DH5NP18-H2 Series A Proximity Sensor
ALLEN-BRADLEY 871TM-DH2NP12-D4 SER.A QUANTITY! N.O. 2mm 10-30VDC PROX. SENSOR
ALLEN-BRADLEY 871TM-DH2NP12-C2 SER.A 10-30VDC PROXIMITY SENSOR
ALLEN-BRADLEY 871TM-B2N12-C2 SER.A ! N.O. SD: 2mm INDUCTIVE PROXIMITY SENSOR
ALLEN-BRADLEY 8-594 PHOTOELECTRIC EM-RELAY SER.B
ALLEN-BRADLEY 8-593 PHOTOELECTRIC EM-RELAY QUANTITY!!!
ALLEN-BRADLEY 8-590 PHOTOELECTRIC EM-RELAY SER.B QUANTITY!!!
Allen-Bradley 8-590 Output Module 2A @ 120V 1A @ 240V ! WOW !
Allen-Bradley 855T-BSBC Series B Accessory Kit
ALLEN-BRADLEY 855T-B24SA1 SER.C QUANTITY 24V SINGLE TONE SOUND BLACK HORN BUZZER
ALLEN-BRADLEY 855E-LL24R SER A 24V RED, in box
ALLEN-BRADLEY 855E-LL24G SER.A QUANTITY! 24V GREEN LED LAMP/BULB FOR STACK LIGHT
ALLEN-BRADLEY 855E-LL24G SER A 24V GREEN, in box
ALLEN-BRADLEY 855E-LL24A SER A 24V AMBER, in box
Allen-Bradley 855E-GPM25 Series A Signal Tower Light Base(Color White)
ALLEN-BRADLEY 855E-G24SA3 SER.A ! QUANTITY! 24V SINGLE TONE GREY HORN BUZZER
ALLEN-BRADLEY 855E-24DN4 ! QUANTITY SER.A RED STEADY INCANDESCENT STACK LIGHT
ALLEN-BRADLEY 852S-NSB SERIES G SOLID STATE TIMER 110V-120V 50HZ-60HZ TESTED!!
ALLEN-BRADLEY 845H-SJHC24DNY2C SER.B ! ENCODER OPTICAL INCREMENTAL
ALLEN-BRADLEY 845H-SJDZ23DBY1C SERIES C ENCODER IN BOX!!
ALLEN-BRADLEY 845H-SJDZ23CBY1C ENCODER, INCREMENTAL 8-24V - !
ALLEN-BRADLEY 845H-SJDZ13EBY1C SER.B ! ENCODER OPTICAL INCREMENTAL
ALLEN-BRADLEY 845H-SJDN12FWY2C SER.B ! ENCODER OPTICAL INCREMENTAL
ALLEN-BRADLEY 845D-SJHZ25BDCK1 SER.A ! ENCODER OPTICAL ABSOLUTE
ALLEN-BRADLEY 845D-SJHZ24AGFW4 SER.A ! QUANTITY! ENCODER OPTICAL ABSOLUTE
ALLEN-BRADLEY 837-A61 BULLETIN 837 TEMPERATURE SWITCH
ALLEN-BRADLEY 836T-T250JX9 VACUUM PRESSURE CONTROL QUANTITY!!!
Allen-Bradley 825-PDN Series A DeviceNet Communications Card
ALLEN-BRADLEY 825-MCM630 OVERLOAD Ie= 160...630A 1000V 50/60Hz SER.A QUANTITY!!!
Allen-Bradley 817U Thermistor
ALLEN-BRADLEY 817-M* THERMISTOR PROTECTION RELAY SER. A 110V 2VA
ALLEN-BRADLEY 817-AD SER.A QUANTITY! 110V THERMISTOR PROTECTION RELAY
ALLEN-BRADLEY 813S-VOC SER.B LINE VOLTAGE MONITOR RELAY ! !
ALLEN-BRADLEY 809-A03E ! INSTANTANEOUS TRIP CURRENT RELAY 1.9 - 6.1A
ALLEN-BRADLEY 802T-W1 Roller Lever .75DX9/32WD WOW
ALLEN-BRADLEY 802PR-LBAJ1 /E INDUCTIVE PROXIMITY SENSOR 20-250V AC/DC 25mA
ALLEN-BRADLEY 802PR-LBAB1 PROXIMITY SENSOR 20-250VAC/DC AC 4-25mA DC 2-25mA N.O.
ALLEN-BRADLEY 802C-E53M6B PULL SAFETY SWITCH BUL. 802C SERIES: A REV: A
ALLEN-BRADLEY 800T-XD6 SER.D !! QUANTITY!! 1NC CONTACT BLOCK
ALLEN-BRADLEY 800T-XD2 SER.D ! QUANTITY! 1N.C. CONTACT BLOCK
ALLEN-BRADLEY 800T-XD1P SER.F ! 1N.O. SEALED SWITCH CONTACT BLOCK
ALLEN-BRADLEY 800T-XD1 ! QUANTITY! SER.D 1NO CONTACT BLOCK
ALLEN-BRADLEY 800T-XD1 IN BOX CONTACT BLOCK (2F0)
ALLEN-BRADLEY 800T-XAR SER.A ! 1N.O./1N.C. CONTACT BLOCK LOGIC REED BLOCK QTY
ALLEN-BRADLEY 800T-T3P1GALX 3-POS JOY STICK 600V 10A - ! QUANTITY!
ALLEN-BRADLEY 800T-T2H1 2 WAY MAINTAINED TOGGLE JOYSTICK
ALLEN-BRADLEY 800T-P16 *NIB* PILOT LIGHT TYPE 4/13 SER T 120V (2F0)
ALLEN-BRADLEY 800T-NG11KF4C 4-POS SELECTOR SWITCH - !
Allen-Bradley 800T-J91 Selector Switch
Allen-Bradley 800T-H5A Series T 2 Position Spring Return Selector Switch
ALLEN-BRADLEY 800T-H48B SELECTOR SWITCH LOCKING - !
ALLEN-BRADLEY 800T-A SER. T BLACK PUSH BUTTON OPERATOR SWITCH - NNP - FREE SHIP
ALLEN-BRADLEY 800T-16HG2KB6 GREEN SELECTOR SWITCH
ALLEN-BRADLEY 800MS-JX2R SELECTOR SWITCH UNIT SER.A !!
ALLEN-BRADLEY 800L-18L24 INDICATOR LIGHT RED
ALLEN-BRADLEY 800H-QRTH24G PUSH TO TEST GREEN 24V - QUANTITY!
ALLEN-BRADLEY 800H-PRBH16R PUSH TO TEST RED 120V - QUANTITY!
ALLEN-BRADLEY 800H-PRBH16G ILLUMINATED PUSHBUTTON GREEN 120V
ALLEN-BRADLEY 800H-PR16 PILOT LIGHT RED 120V - QUANTITY!
Allen-Bradley 800H-NP11 Series A 1" Conduit Plug 800HNP11
ALLEN-BRADLEY 800H-JP42KB7 KEY OPERATED SELECTER SWITCH 3 POS - ! QUANTITY!
ALLEN-BRADLEY 800FM-KM34MX22 KEY MAINTAINED SELECTOR SWITCH - ! QUANTITY!
ALLEN-BRADLEY 800FM-KM21 2 POSITION KEY MAINTAINED SELECTOR SWITCH SER: A !!
ALLEN-BRADLEY 800E-3DB5 ! QUANTITY! 120V SER.A BASE MOUNT MODULE
ALLEN-BRADLEY 77135-146-52 ! QUANTITY! 2711 MEMORY CARD RETAINER KIT
ALLEN-BRADLEY 74101-915-16 1336-GM1 REMOTE I/O BORD
ALLEN-BRADLEY 71A86 * * OPERATING COIL SIZE 1 110-120V (2F0)
ALLEN-BRADLEY 709-DOD SER.CC SIZE 3 120V COIL 3PH 600V 50HP STARTER
ALLEN-BRADLEY 709-AOD103 SER.K 460-575V 5HP SIZE 0 120V COIL STARTER
ALLEN-BRADLEY 700-ZBR520AZ1 SAFETY RELAY 120V 24V SER.A
Allen-Bradley 700-TBR60 Series A Terminal Block Relay 700TBR60
ALLEN-BRADLEY 700-TBR60 60VDC COIL 6A 250VAC RELAY W/ 700-HLT1L160 BASE QUANTITY
Allen-Bradley 700-TBR24 Series A Terminal Block Relay 700TBR24
ALLEN-BRADLEY 700-TBR24 24VDC COIL 6A 250VAC RELAY W/ 700-HLT1Z24 BASE QUANTITY!
ALLEN-BRADLEY 700S-P310A1 SAFETY RELAY 3NO/1NC 120V
Allen-Bradley 700-SE10GZZ24 Series A Solid State Relay 700SE10GZZ24
ALLEN-BRADLEY 700S-DCP620Z24 8 POLE 6 N.O. 2 N.C. 24VDC SAFETY CONTROL RELAY
ALLEN-BRADLEY 700S-CF620ZJC SAFETY CONTROL RELAY
ALLEN-BRADLEY 700S-CF440ZJC SER.A QUANTITY! 1N/O 3N/C 24VDC COIL SAFETY RELAY
ALLEN-BRADLEY 700S-CF440DJC SER.A 24VDC COIL SAFETY RELAY * QUANTITY!!!
