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PLC与继电器控制系统的比较
1 控制方式：
继电器的控制是采用硬件接线实现的，是利用继电器机械触点的串联或并联极延时继电器的滞后动作等组合形成控制逻辑，只能完成既定的逻辑控制。
PLC采用存储逻辑，其控制逻辑是以程序方式存储在内存中，要改变控制逻辑，只需改变程序即可，称软接线。
2 控制速度
继电器控制逻辑是依靠触点的机械动作实现控制，工作频率低，毫秒级，机械触点有抖动现象。
PLC是由程序指令控制半导体电路来实现控制，速度快，微秒级，严格同步，无抖动。
3 延时控制
继电器控制系统是靠时间继电器的滞后动作实现延时控制，而时间继电器定时精度不高，受环境影响大，调整时间困难。
PLC用半导体集成电路作定时器，时钟脉冲由晶体振荡器产生，精度高，调整时间方便，不受环境影响。
天然气作为国家的重要能源和工业原料，随着我国国民经济的迅速发展，大中小型企业对它的需求迅速增加；同时由于天然气价格的提高，对天然气流量准确计量的要求越来越迫切。目前市场有各种各样的流量计可用于测量天然气的流量。其中差压式（孔板、喷嘴）流量计因其设计规范简单、牢固、一致性好，不需要实流标定等诸多优点被广泛用作贸易结算流量计。
由于天然气流量计量是非常复杂的，所以使用流量计有诸多不足之处。
首先，流量计的读数需专人手工抄表，就大中型轻烃计量站来说，有30余条天然气管线，共计103个测试点，而且测试点分布面积范围广，并且比较分散，这样就耗费了较多的人力物力。
其次，不管采用哪种流量计，往往需要采用补偿措施来提高测量的准确性。用现代技术实施自动补偿是流体计量领域里的重要课题。所谓流量补偿就是对流量计读数的系统误差修正。流量检测装置的系统误差多数是流体性质及条件（如温度、压力、成分及流量范围等）变化引起的。流量计输出信号与被测流量之间的刻度关系只能依据某一特定工艺状况来确定。如果流量计的实际刻度系数已经发生变化，这时仍按原刻度关系读取流量，显然会产生误差。在一些需要精确计量的场合或工况波动范围大而且波动频繁的场合，必须采用补偿措施。流体计量补偿技术就是针对不同流量计，检测不同流体而建立的一种修正方法。由仪表读数准确推算出流体的实际流量，因而流量补偿技术在流体计算中具有重要意义。
由于电动单元仪表的出现，八十年代开始应用电动单元组合仪表的变送器和运算单元建立自动补偿系数，不但实现了自动连续补偿，检测精度也有所提高。它通过变送器同时检测出天然气的静压、差压和温度等参数，并将它们转换为相应的统一的电流信号，按某种运算关系把信号送入计算单元进行运算，输出代表准确流量的信号，经显示仪表显示出流量值和累积流量。单元组合仪表具有通用性强，组成系统比较灵活，自动化程度高，无须人工计算，温度、压力和差压在线检测计算，较符合流量测量理论。其次，目前普遍采用的电容式变送器抗干扰能力强，无机械摩擦磨损，因此系统精度较高。但是在计算方面对标准中各参数的修正问题（如天然气组成成分及其摩尔分量不断变化），从而带来公式引用误差。而且这类补偿装置使用的仪表数量大，补偿装置一次性投资大，而且一套补偿装置只能进行一个流路的流量补偿。这些缺点使它的应用受到限制。
计算机和网络的推广和普及，极大地推动了补偿技术的发展。根据节流式流量测量理论可知：瞬时流量是流体工况（差压、绝对静压、温度）的函数。由于工况参数一般都是变动的，因此累积流量用工况平均参数计算和用瞬时参数计算累加，其结果是不一样的。以瞬时参数计算并累计流量才符合要求。由于现在的计算机具有极强的存储能力和极快速的运算能力，再配套高精度的智能变送器、数据采集卡，就可以完成数据采集处理、数据存储、报表打印和报警等功能，极大的减轻人员的劳动强度。通过计算机联网，就可以实时测控天然气输气管道的数据，实现安全生产，同时使管理层根据现场生产状况进行快速决策。运用计算机计算流量的最大优点是：全部采用实时参变量（差压、绝对静压、温度等），因此就不存在对差压、绝对静压、温度等参数的补偿问题；同时与温度、压力、差压有关的参量（如孔板内径、动力粘度和压缩因子等）也随各相关量变化而变化，从而使补偿装置的成本急剧下降。在实际应用中，当要对天然气流量计算式中某些需经常改变的量（如天然气组成成分及其摩尔分量）进行修改时，可以通过计算机软件来完成。而且还可对含水的天然气进行含水补偿（即扣除水蒸气的体积流量）。因而从理论上讲，运用计算机的实时流量计算系统可构成目前和将来最理想和最完善的节流式流量计量系统。
二、 系统概述
完成一个天然气计量系统项目涉及大小工作站十余个，每个工作站配有高精度的压力、差压、温度变送器、数据采集板卡进行天然气流量状态的测量、采集，再通过上位机使用MCGS组态软件，从而完成现场数据采集、数据存储、报表打印和报警等功能，便于现场工作人员对生产的监视及控制。通过计算机联网，将各计量站数据传到调度室HP服务器中，使总调值班人员方便的掌握全系统天然气产量，流向及报警等信息，及时的调整天然气走向。调度HP服务器安装了MCGS组态软件www版本，现场工作站通过远程微波，MODEM，串口通讯等通讯方式把现场数据传送到调度服务器上，组态并在局域网上发布，形成基于WEB的上位机管理系统，管理机通过浏览Internet，可以实时的查看数据曲线，报表，历史存盘数据和实时数据等功能。基于WEB的上位机管理系统能够充分发挥服务器和管理机的功能，充分使用管理机的图形能力来绘制动画，并发挥服务器的数值计算能力，进行统计汇总。可以使得整个系统的应用潜力得到充分发挥。
三、工作站简介
Moeller 0188-0135 Cylinder 0635-H58H - No Box
MOELLER 0117RG39 **NNB**
MOELLER 0.4A, 660V MANUAL MOTOR STARTER PKZM 1-0.4-NA
Moeller 0 to 300 Psi Gage 76526 (U1)
MOELLER ~ PKZM 1–16~16A~660 V~ AC 3~VDE 0660~IEC 157 ~ MOTOR STARTER SWITCH
Moeller / Kloecker Moeller EMR4-F500-2 Phasenfolgerelais
Moeller / Kl?ckner Moeller ZB4-508-KB1 Verbindungskabel
Moeller / Kl?ckner Moeller ZB4-501-IF1 SUConET K-Interface - -
Moeller / Eaton Aufbaugeh?use Geh?use - M22-I6 - 6 Fach - 216540 - NEU & OVP
MOELLER (FAZ-D16/3) D16 16 AMP 15 KA 278896 TRIPLE POLE MCB CIRCUIT BREAKER
MOELLER (FAZ-D10/3) D10 10 AMP 15 KA 278892 TRIPLE POLE MCB CIRCUIT BREAKER
MOELLER (FAZ-C10/3) C10 10 AMP 15 KA 278869 TRIPLE POLE MCB CIRCUIT BREAKER
Moeller (F&G) Fehlerstromschutzschalter F7-63/4/01-A
Moeller (1 Stück) - Leistungsschütz 7,5kW/400V,DC DILM17-10(RDC24) #GR-461-4
Moeller ( EATON ) EMT6 DB 2S Motorschutzrelais Temperaturüberw. AC 230 V in OVP
Moeller ( EATON ) EMT6 DB 2S Motorschutzrelais Temperaturüberw. AC 230 V in OVP
Moeller # PKZMO-1-T Manual Starter Motor Protector
MOELLER - ZB32-2,4 - RELAY, OVERLOAD, FOR DILM17-DILM32
Moeller - X Pole PLSM-D63/3-MW - 63a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D6/3-DW - 6a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D50/3-MW - 50a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D40/3-DW - 40a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D25/3-DW - 25a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D20/3-MW - 20a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D20/3-DW - 20a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-D10/3-DW - 10a Type D Triple Pole MCB In Box
Moeller - X Pole PLSM-C6/3-DW - 6a Type C Triple Pole MCB In Box
Moeller - X Pole PLSM-C50/3-DW - 50a Type C Triple Pole MCB In Box
Moeller - X Pole PLSM-C25/3-DW - 25a Type C Triple Pole MCB In Box
Moeller - X Pole PLSM-C10/3-DW - 10a Type C Triple Pole MCB In Box
Moeller - X Pole PKS6-40/1N/B/003 - 40a Type B RCBO
Moeller - X Pole PKS6-16/1N/C/003 - 16a Type C RCBO
Moeller - X Pole PKS6-10/1N/B/003 - 10a Type B RCBO
Moeller - X Pole PFIM-100/2/003 - 100a 30mA Type AC Double Pole RCD
MOELLER - TO-2-1/I1/SVB - 3 POLE ENCLOSED ISOLATOR 20A 4KW
MOELLER - T0-2-1/I1H/SVB - ISOLATOR, PLASTIC, ENCL, 20A, 3POLE
MOELLER - T0-2-1/E - MAINS SWITCH, T0-2-1/E
MOELLER - T0-1-102/I1/SVB - SWITCH, PLASTIC, ENCL, 20A, 2POLE
Moeller - Schütz- Hilfschütz
MOELLER - P1-25/I/SVB - 3 POLE ENCLOSED ISOLATOR 5.5KW
MOELLER - Motorschutzschalter - PKZM0-0,63
MOELLER - M22-WRK3+M22-A - ACTUATOR, THUMB, 3WAY
MOELLER - M22-WK+M22-A - ACTUATOR, THUMB, 2WAY
MOELLER - M22-KC10 - ConTACT BLOCK - (Lot of 3 Each - )
MOELLER - M22-KC01 - ConTACT ELEMENT (Lot of 3 Each)
MOELLER - M22-I6 - SURFACE MOUNTING IP66 PUSH BUTTON ENCLOSURE, 6 GANG
MOELLER - M22-I3 - SURFACE MOUNTING IP66 PUSH BUTTON ENCLOSURE, 3 GANG
MOELLER - M22-I3 - SURFACE MOUNTING IP66 PUSH BUTTON ENCLOSURE, 3 GANG
MOELLER - M22-I2 - SURFACE MOUNTING IP66 PUSH BUTTON ENCLOSURE, 2 GANG
MOELLER - Leistungsschalter Motorschutz - NZM7-100N-M8 neu OVP
Moeller - LED- SL-LED grün
Moeller - LED- SL-LED gelb
MOELLER - Haupt-/Not-Aus-Schalter 6P 32A IP65 - T3-4-15682/EA/SVB-SW
MOELLER - Haupt-/Not-Aus-Schalter 6P 32A IP65 - T3-4-15682/EA/SVB-SW
MOELLER - Grundger?t 3p o.Ausl?serblock - PKZ2
MOELLER - FAZ-C16/3 - CIRCUIT BREAKER, 16A, 3POLE
MOELLER - FAZ-C10/1 - CIRCUIT BREAKER, 10A, 1POLE
MOELLER - FAZ-C1/1 - CIRCUIT BREAKER, 1A, 1POLE
Moeller - Eaton Ein-Aus-Schalter P3-63/IVS
Moeller - Eaton Ein-Aus-Schalter P3-63/IVS
MOELLER - EATON DILMC65 ( RDC24 ) LEISTUNGSSCHüTZ SCHUTZE 24-27 V DC 30KW/400V
MOELLER - DILR31 - ConTACTOR - 120V
MOELLER - DILEM-10-G(24VDC) - CONTACTOR, MINI, 4KW
Moeller - DIL2M-G, NDIL2M, FDBDIL Motor Contactor Starter
Moeller - DIL2M Motor Contactor 110V COIL
Moeller - DIL00M-10
MOELLER - Anschlussblock Klemmblock 160A - K95/5
MOELLER - 22DILEM - ConTACT BLOCK, 2NO/2NC
M8-8611ET ROLLER PLUNGER SWITCH replac MOELLER ATO-11-S-I/RS OMRON D4N-4132
M8-8611ET ROLLER PLUNGER SWITCH replac MOELLER ATO-11-S-I/RS OMRON D4N-4132
M8-8611E ROLLER PLUNGER SWITCH replac MOELLER ATO-11-S-I/RS OMRON D4N-4132 AZD1
M8-8611E ROLLER PLUNGER SWITCH replac MOELLER ATO-11-S-I/RS OMRON D4N-4132 AZD1
M8-8608ET ADJUSTABLE ROLLER LEVER SWITCH REPLACES MOELLER ATO-11-S-I/V AZD1008
M8-8608E LIMIT SWITCH 6A REPLACES MOELLER ATO-11-S-I/V
M8-8607ET ADJUSTABLE ROD LEVER SWITCH REPLACES MOELLER ATO-11-S-I/H 6A AZD1007
M8-8607E ADJUSTABLE ROD LEVER LIMIT SWITCH REPLACES MOELLER ATO-11-S-I/H AZD1057
M8-8606ET FLEXIBLE PLASTIC ROD WOBBLE LEVER SWITCH REPLACES MOELLER ATO-11-S-I/F
M8-8606E FLEXIBLE PLASTIC ROD WOBBLE LEVER SWITCH REPLACES MOELLER ATO-11-S-I/F
M8-8604ET ROLLER SHORT LEVER ARM SWITCH REPLACES MOELLER ATO-11-S-I/R D4N-4125
M8-8604E ROLLER SHORT LEVER ARM SWITCH REPLACES MOELLER ATO-11-S-I/R AZD1004
M8-8603ET ONE-WAY ROLLER ARM LEVER VERTICAL SWITCH replac MOELLER ATO-11-S-I/WR
M8-8602ET ONE-WAY ROLLER ARM HINGE LEVER SWITCH replac MOELLER ATO-11-S-I/AR
M8-8601ET PUSH DOME PLUNGER LIMIT SWITCH 6A REPLACES AZD1001 MOELLER ATO-11-S-I
M8-8601ET PUSH DOME PLUNGER LIMIT SWITCH 6A REPLACES AZD1001 MOELLER ATO-11-S-I
M8-8601E PUSH DOME PLUNGER LIMIT SWITCH 6A REPLACES D4N-4131 MOELLER ATO-11-S-I
M8-8601E PUSH DOME PLUNGER LIMIT SWITCH 6A REPLACES D4N-4131 MOELLER ATO-11-S-I
M22-WRS3 +M22-A Moeller - M22-Wrs3 +M22-A - Actuator , Keyswich , 3Way
M22-WRS+M22-A Moeller - Actuator , Keyswich , 2Way
M22-WRLK-R+M22-A - EATON MOELLER - ACTUATOR, RED, 2WAY
M22PVLM22AM22XAK Moeller Switch , Pushbutton , Estop , 90mm Lbl
M22-PV+M22-A+M22-XAK Moeller - Switch , Pushbutton , Estop , 90mm Lbl
M22-PV/KC11/IY Moeller Enclosure , Estop Pushbutton
M22-DRP-R+M22-A Moeller - M22-Drp-R+M22-A - Switch , Pushbutton , Mushroom , Red
M22-DRL-Y+M22-A Moeller - Switch , Pushbutton , Illum , Yellow
M22-DRL-B+M22-A - EATON MOELLER - SWITCH, PUSHBUTTON, ILLUM, PROG, BLUE
LV6 Kl?ckner Moeller SPS EBE231 B EBE 231
Lot of 9 Moeller X Pole PLSM-C16/1-AS 1P Circuit Breakers
LOT OF 8 MOELLER EK10 AUXILIARY ConTACT 600VAC * *
LOT OF 7: Klockner Moeller DIL R 40 Contactors + Auxiliaries 22DIL,04DIL,40DIL
LOT OF 7 MOELLER FAZ-2-C6 CIRCUIT BREAKER * OUT OF A BOX*
LOT OF 6 MOELLER 0117-RG87 PUNCHES RND 20 DIA X 25, P=9.58 B=12 P/S
LOT OF 6 KLOCKNER MOELLER BREAKER FAZNC4-2 TWO POLE 277/480VAC
Lot of 6 Moeller Manuel Starters PKZM 1-1,6
LOT OF 6 MOELLER 04DIL MINIATURE ConTACTOR * *
LOT OF 5 MOELLER M22-KC01 ConTACT BLOCK * *
LOT OF 5 KLOCKNER-MOELLER RWK3R SELECTOR SWITCH * IN A BOX*
LOT OF 5 KLOCKNER-MOELLER AD-E ADAPTER EXTENSION PIECE * IN A FACTORY BAG*
LOT OF 5 KLOCKNER-MOELLER 40DIL SMALL ConTACTOR * *
LOT OF 5 KLOCKER MOELLER EFC * OUT OF BOX*
LOT OF 4: Klockner Moeller DIL R 40 + 22 DIL M + 04 DIL Contactor, Relay
LOT OF 4 MOELLER FAZN B6 CIRCUIT BREAKER * OUT OF A BOX*
LOT OF 4 MOELLER 20DIL AUXILIARY ConTACT BLOCK * IN A BAG*
LOT OF 4 MOELLER 11DILM AUXILIARY ConTACTS * *
LOT OF 4 KLOCKNER-MOELLER RWK3R SELECTOR SWITCH * IN A BOX*
LOT OF 4 KLOCKNER-MOELLER EZ1 THERMAL OVERLOAD RELAY ACCESSORIES * *
LOT OF 4 KLOCKNER MOELLER NHi11-PKZM1 * IN BOX*
LOT OF 4 KLOCKNER MOELLER FAZN B10 * *
Lot of 4 Klockner Moeller DIL R 40-G Contactor Relays w/ VG B DIL 24 Suppressor
Lot Of 3 Klockner Moeller Pkzm3-U-Na Manual Motor Starter
Lot of 3 Moeller Track Mounted Breakers (See Add. Info for Specs)
LOT OF 3 MOELLER FAZ-C10 CIRCUIT BREAKER * OUT OF A BOX*
LOT OF 3 MOELLER FAZ-3-C20 CIRCUIT BREAKER * OUT OF A BOX*
LOT OF 3 MOELLER FAZ-2-C4 CIRCUIT BREAKER * OUT OF A BOX*
Lot of 3 Moeller FAZ-2 S10 10 Amp Breaker Switches
LOT OF 3 MOELLER DILEM-10-G ConTACTORS 15AMP DILEM10G
Lot of 3 Moeller DIL EM4-G Contactor 4 Pole 24VDCCoil 15A 400V VAC 4kW
LOT OF 3 MOELLER BFT 125/6 * OUT OF A BOX*
LOT OF 3 MOELLER 31DILM MINIATURE ConTACTOR * IN A BAG*
LOT OF 3 MOELLER 13 DIL MINIATURE ConTACTOR 13-DIL 13DIL
LOT OF 3 KLOCKNER-MOELLER 20DIL AUXILIARY ConTACT MODULE * IN A BOX*
LOT OF 3 KLOCKNER MOELLER SELECTOR SWITCH RWK3R * IN BOX*
LOT OF 3 KLOCKNER MOELLER HI11-P1/P3 AUX. SWITCH * IN BOX*
LOT OF 3 KLOCKNER MOELLER FAZ-S6 SUPPLEMENTARY PROTECTORS, 230/415 V, FAZS6
LOT OF 3 KLOCKNER MOELLER DIL 00M-10 ConTROL (300)
LOT OF 3 KLOCKNER MOELLER ConTACTOR 11 DIL EM * OUT OF BOX*
Lot of 3 Klockner Moeller Circuit Breakers FAZN C20-2 / FAZN C40-3 / 20A / 40A
LOT OF 3 - KLOCKNER MOELLER DIL R 31 Contactor 500V~/600V 10A
LOT OF 2 MOELLER DILM17-10 Contactor DILM1710 DILM17
LOT OF 2 MOELLER PROTECTOR FAZ/FIP-XHI11 * OUT OF BOX*
Lot Of 2 Moeller PKZM0-6.3 Manual Motor Starter Switch/CircuitBreaker Ser. No 04
Lot of 2 Moeller PKZM0-10/PKZM0-4 Motor Protector Circuit Breakers
Lot of 2 MOELLER P1-25 SWITCH 3 PHASE
Lot of 2 Moeller LS-11 Plunger Roller Mechanical Limit Switches
LOT OF 2 MOELLER LAMP MODULE M22-CLED-R (RED) * OUT OF BOX*
LOT OF 2 MOELLER LAMP MODULE M22-CLED-B (BLUE) * OUT OF BOX*
LOT OF 2 MOELLER LAMP MODULE M22-CLED230-G (GREEN) * OUT OF BOX*
LOT OF 2 MOELLER DP-M22-DL-W ILLUMINATOR * IN BOX*
Lot of 2 Moeller DILM820-XHI11-SI Contact Block
Lot of 2 Moeller DILM1000-XHl11-Sl Contact Block
LOT OF 2 MOELLER DIL00M ConTACTOR RELAYS DIL-00M
LOT OF 2 MOELLER 13DIL MINIATURE ConTACTOR * IN A BAG*
LOT OF 2 KLOCKNER-MOELLER FAZ-2-S2 CIRCUIT BREAKER * IN A BOX*
Lot of 2 Klockner-Moeller DIL08-53 RELAY
LOT OF 2 KLOCKNER MOELLER U-PKM0 * IN A BOX*
Lot of 2 Klockner Moeller S2 Mounting Bracket Old Stock Box
LOT OF 2 KLOCKNER MOELLER PKM0-2,5 *NICE*
LOT OF 2 KLOCKNER MOELLER ConTACT BLOCK K-NA * OUT OF BOX*
LOT OF 2 KLOCKNER MOELLER ConTACT BLOCK K-NA * OUT OF BOX*
Lot of 18 KLOCKNER MOELLER F CONTACT
Lot of 15) Moeller RLF-GE Orange Indicating Pilot Light Push Button +Priority SH
Lot of 15) Moeller RLF-GE Orange Indicating Pilot Light Push Button +Priority SH
Lot Of 11 Moeller FAZ Circuit Breaker 1 pole
Lot Of 10 Moeller Punches 1291-0313
Lot of (4) Klockner-Moeller RT110 RP-RTX Industrial Red Stop Push Button
Lot of (4) Klockner Moeller Sector Switch RWK3R NNB + Free Priority Shipping!!!
Lot of (4) Klockner Moeller Sector Switch RW1R with BE3 Adapter Mounting Bracket
Lot of (4) Klockner Moeller Red Emergency Industrial Stop Push Button NNB
Lot of (4) Klockner Moeller RDH-9RT110 Red Emergency Stop Push Button
Lot of (4) Klockner Moeller RDH-9RT110 Red Emergency Stop Push Button
LOT OF (4) KLOCKNER MOELLER ConTACT BLOCK ASSEMBLIES 1 N.O. 1 N.C. MODEL BK11