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：
Glossary
Process station:
This term is used to describe AC800F controllers (field controllers) and rack-mounted controllers. A process station can be designed to be redundant
configuration and non-redundant configuration.
AC800F :
This term is used to describe the AC800F Field Controller type of process station. A redundant process station consists of 2
AC800F controller.
Rack mounted process station:
This term is used to describe a rack-mounted type of process station. A redundant process station contains 2 rack-mounted CPUs.
This term is used to describe a single, non-redundant process station.
In the investment of modern automation system, due to the hardware equipment department
It only takes up less cost in the whole system, then write
