综上所述，在恶劣环境中，使用PLC控制机构设备，生产流水线和生产过程的自动控制将越来越广泛。但是，这种新型控制装置在推广使用中尚有一些问题困扰着用户，主要集中在两个方面，一是可靠性问题，二是价格问题。
用新型控制装置实现老设备改造与生产过程自动化，提高劳动生产率，改善企业管理，这是提高企业经济效益的必要措施，但如何正确处理这种关系，本文提供一些数据资料作为用户参考。
1、可靠性问题
据有关资料提供数据表明：国外一般中小型PLC，如日立、西门子、IPM，平均无故障时间高达10万h。即使大型PLC平均无故障时间也在4～5万h之间。因此，制造厂商认为可靠性已不存在问题。就可靠性而言，继电接触器是望尘莫及的。所以，对于日立、西门子、IPM等产品资料中可靠性不再是一项技术指标。
2、PLC的经济综合分析
对PLC的经济分析，应从以下几方面考虑：
（1）从影响成本的各个因素综合考虑从目前生产设备控制装置来说，有三种类型：①继电器控制。②半导体器件控制。③PLC控制。
价格仅是选择PLC品牌的一个因素，而可靠性是选择时需要考虑的又一个因素。
JUNIPER NETWORKS PB-AS2 ADAPTIVE SERVICES II PIC NOB
NEW OPEN BOX 90 DAY WARRANTY
Juniper M40 Router
Juniper JXU-16GE-TX-S UPIM 16Port 1000bT for J & SSG
90 Day warranty – Free Overnight Shipping!
New Juniper PC-1OC192-SON-SR2 OC192 PIC M160/T320/T640
1 YEAR WARRANTY ( 10 Million in Stock, See Our Store )
RE-1600-2048-R Juniper RE-1600 T1600 T640 T320 4.0
Juniper P-1GE-LX-B 1port Gig Eth PIC M20 M40 FREESHIP
JUNIPER PC-TUNNEL – Tunnel Services PIC, 10Gbps
JUNIPER ES2-4GS1-MOD-A E320 4GB LINE MODULE IPU2AFJ
One-day shipping available
Juniper PB-4OC12-SON-SMIR Module GF
Juniper PB-2GE-SX Physical Interface Card – M160
SHIPS TODAY! 1 YR WRNTY! 5+ Avail. Make an Offer!
One-day shipping available
JUNIPER IB-OC192-SON-SR2 SONET/SDH STM-64/OC-192 M160
One-day shipping available
JUNIPER P-MCDS3 M20 & M40 TESTED WITH WARRANTY
Juniper Networks – Expansion module EX-UM-2X4SFP
Brand New & Ready To Ship From A US Authorized Reseller
NEW JUNIPER JXU-8GE-TX-S Juniper 8-port Gigabit Etherne
Juniper OC3/OC12-POS – RF
Juniper SA6000 Secure Access 1X AC PS 1X HD GF
JUNIPER SFM-16-S-C SWITCHING & FORWARDING MOD IPC925S
One-day shipping available
Juniper Netscreen NS-ISG-1000 VPN Firewall AC
Juniper IB-OC192-Son-SR2-B Sonet STM-64 Interface
One-day shipping available
Juniper EX 3200 24T – Switch – L3 – managed EX3200-24T
Juniper PE-1CHOC12-DS3-SMIR Channelized OC-12 to DS3
One-day shipping available
Juniper Networks (SRX210H-POE) SRX210 Services Gatew…
Buy this product now!
One-day shipping available
Prostrata juniper Bonsai Tree #02
SIEMENS/JUNIPER OC3/OC12-POS ERX 4 PORT OC3 1 PORT
One-day shipping available
Juniper PB-AS2 ADAPTER SERVICES II MODULE
Juniper P-1GE-SFP module, 1 YEAR Warranty
Juniper Networks HCM-M10i-S Chassis Manager Board M10i
Juniper EX3200-24T 24-Port 10/100/1000 8-ports PoE
JUNIPER NETWORKS P-1OCHE1-RJ48 DSO SERVICES PIC REFURB
TESTED 90 DAY WARRANTY
New Surplus Juniper PB-4GE-SX 4port Gig Eth PIC SX M160
90 Day Warranty – Free Shipping
Enlarge
Juniper PB-12FE-TX-MDI-B 12 Port Fast Ethernet PIC M120
90 Day Hardware Warranty – Free Shipping!
JUNIPER NETWORKS CB-L-T-S CONTROL BOARD NEW OPEN BOX
Lot 50 Juniper NetScreen 10User VPN/Firewall NS-5GT-001
Expedited shipping available
Juniper Networks PB-1GE-SFP 1 Port Gigabit Ethernet PIC
Juniper ERX-2GE-IOA 2+2 Port GE IOA ERX 1440 ERX-GE-MOD
90 Day Warranty – Free Overnight Shipping!
JUNIPER NETWORKS T320-FPC1 FLEXIBLE PIC CONCENTRATOR
NEW OPEN BOX 90 DAY WARRANTY
NEW JUNIPER EX-SFP-10GE-LRM Juniper 10GBase-LRM SFP+ Tr
M40E-FPC1-EP M40E-FPC1-EP-B Juniper Enhanced Plus M40E
Juniper Networks M160-SFM Switching & Forwarding Module
One-day shipping available
QTY Juniper PB-2GE-LX M160 T640 M320 PIC Ethernet T320
Juniper P-1GE-SFP Module M20 M10 GF
Juniper Compatible SFP-1OC48-IR Optic Module
SHIPS TODAY! *$100M Inv* 1 YR WRNTY! 2+ Avail.
One-day shipping available
Juniper Networks J4300BASE-AC Service Router
JUNOS 7.2R1.7 OS Comes with blanks and Brackets
One-day shipping available
Enlarge
** Juniper EX3200-24T L2/L3 virtual chassis switch **
Tested with Warranty! ***Call (415) 483-1190 ***
One-day shipping available
