一、PLC與DCS比較

    如果按從弱至強(qiáng)將PLC與DCS的性能劃分為1至10個(gè)等級(jí)，則可將它們的對(duì)比列于表1

    表1PLC與DCS的比較

    比較項(xiàng)目PLC控制DCS控制

    高速順序控制106

    復(fù)雜過程控制610

    硬件可靠性98

    聯(lián)網(wǎng)和通訊功能48

    管理能力39

    系統(tǒng)診斷和報(bào)警38

早期的PLC以數(shù)字量的順序控制為主。隨著PLC功能不斷擴(kuò)充，PLC增加了模擬量控制功能、PID調(diào)節(jié)功能、通訊聯(lián)網(wǎng)功能及分級(jí)控制功能等，在過去DCS占統(tǒng)治地位的化工、冶金等行業(yè)也可由PLC進(jìn)行控制。但PLC難以組成大型、復(fù)雜、綜合的系統(tǒng)，如果過多的PC企圖通過網(wǎng)絡(luò)與過多的PLC通訊，則可能導(dǎo)致瓶頸現(xiàn)象及計(jì)時(shí)上的困難。

    DCS是由模擬儀表控制系統(tǒng)發(fā)展而來，初期的功能以回路調(diào)節(jié)為主，之后又加入了順序控制的功能。DCS的設(shè)計(jì)思想是操作管理集中，控制分散以提高整個(gè)系統(tǒng)的可靠性及管理能力。DCS的上述優(yōu)勢(shì)使它在控制系統(tǒng)的高端市場仍占主流。但DCS比PLC價(jià)位高，對(duì)一些資金有限的中小型企業(yè)有時(shí)難以承受。

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 ALCO CONTROLS FLANGE SET MODEL# RX-173 3LBS. 7/8" ODF

HUMPHREY PNEUMATIC CYLINDER MODEL # 4-DP-4 STROKE: 4.0" BORE: 2.0"

FABCO PNEUMATIC AIR CYLINDER # E121-XDR-BFR STROKE: 0.958"

DEUBLIN ROTARY UNION # 255-000-019 3/4"NPT TO 1/2"NPT

STRAHMAN VALVES 3/4" BRASS NOZZLE 1LB

SMC PNEUMATIC CYLINDER STROKE: 1.50" # NCGCN32-0150-XC?37 BORE: 32MM

SMC PNEUMATIC CYLINDER STROKE: +/-6" DUAL ENDED # NCGWBA50-0600-X?C37 BORE: 50MM

SAMCO TECHNOLOGIES HYDRAULIC CYLINDER TIE ROD 8" STROKE BORE: 2.5"

ASCO SOLENOID VALVE # WP8320A182 Q AIR 1/4"PIPE 125 PSI 120V. 60HZ. 13.9 WATTS

VERSA 4 WAY VALVE # KSG-4232-HCCA12?0

INGERSOLL RAND PNEUMATIC AIR CYLINDER # 2320-1009-100 10" STROKE

FESTO PNEUMATIC AIR CYLINDER # DSNU1-5/8-14-P 14" STROKE ROD DIA. 0.625"

HANKISON PNEUMATIC FILTER # HF1-12-3 CAT# 3240753

BALDOR SPEED REDUCER # S-926-10-H RATIO: 10:1 TORQUE: 1177 IN-LBS

SEW EURODRIVE GEARHEAD SPEED REDUCER# 80.25.10356.5/0?7 TYPE K46 RATIO: 35.63:1

SEW EURODRIVE GEARHEAD SPEED REDUCER RATIO: 48:1 1.25" BORE

TREND BI METAL THERMOMETER # TI.51 12" STEM -40 T0 120DEG F -40 TO 50DEG C

PARKER PILOT AIR SOLENOID VALVE MODEL# K605903553 WEIGHT: 4LBS

PIAB VACUUM PUMP MODEL# X20A5-BN 1 X 3/8"

ANTUNES CONTROLS PRESSURE SWITCH MODEL# RLGP-A 2" TO 14" WC WEIGHT: 2LBS

NUMATICS AIR FILTER ASSY. MODEL# F30B-06C WEIGHT: 3LBS

ALLEN BRADLEY TIME DELAY RELAY # 849-Z0D321

ALLEN BRADLEY TIME DELAY RELAY # 849-Z0A32

ALLEN BRADLEY TIME DELAY RELAY # 849-Z0D32

SMC SOLENOID VALVE # NVFS3200-3FZ WEIGHT: 1LBS

SMC SOLENOID VALVE # NVFS4100-5FZ WEIGHT: 2LBS

SMC MANIFOLD # NVV5FS4-01T-041 WEIGHT: 9LBS

NUMATICS INC. LUBRICATOR # L 30L04 WEIGHT: 3LBS.

FABCO PNEUMATIC AIR CYLINDER # E221-XK-BFR-MR STROKE: 1.437"

FABCO PNEUMATIC AIR CYLINDER # DSNV-32-80-PPV 3.25" STROKE ROD DIA. 12MM

FESTO PROXIMITY SWITCH # SME0-1-LED-24B 12-27VOLTS 1 AMP 27WATTS

BALDOR 3HP AC MOTOR # CM3704T 208-230/460VAC 60HZ. 1160 RPM 213TC FRAME

BALDOR 2HP SUPER-E SEVERE DUTY AC MOTOR 460VAC 60HZ. 1725RPM 145TC FRAME

BALDOR 2HP SUPER-E MARINE DUTY AC MOTOR 460VAC 60HZ. 1725RPM 143TC FRAME

LEESON 1HP AC MOTOR # 121520.00 208-230/460VAC 60HZ. 1170RPM 145T FRAME

BALDOR 1HP AC MOTOR CAT# M7015 230/460VAC 60HZ. 1750RPM HAZARDOUS DUTY

BALDOR BRUSHLESS AC SERVO MOTOR # BSM4F3-75-D 300VAC MAX. 4000RPM 8.03NM

BAYSIDE RIGHT ANGLE PLANETARY GEARHEAD # RA142-015 RATIO: 15:1 BORE: 0.625"

BALDOR GEARHEAD SPEED REDUCER #F-924-10-B7-G RATIO: 10:1 TORQUE: 893 IN-LBS.

BALDOR GEARHEAD SPEED REDUCER #F926-30-B5-G RATIO: 30:1 TORQUE: 1313 IN-LBS.

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