Why PLC when there is DCS...?

http://cr4.globalspec.com/comment/374728/Re-capacitors-type

Gotta go with PWSlack here. Cost, technical capabilities/preferences of the programmer, system complexity and customer preference all come into play.

http://cr4.globalspec.com/comment/374728/Re-capacitors-type

First of all, please visit my web site. Paricularly the page entitled PLC vs. DDC

www.innovativelogicalcontrols.com

I have been in the instrument & controls industry for over 15 years. I have designed, installed and maintained Honeywell, Siemens (old Landis & Gyr), Carrier CCN, Andover, Circon and other less known manufacturers. For the past three years I have settled on the PLC for all of my jobs. The PLC is robust and tolerant of electrical noise, power failures and an occasional short circuit. I can program ANY solution for a customer's request from simple VAV box control up to chiller & boiler optimization.

One item that the PLC has over DCS or DDC is speed. Picture a conveyor belt processing bottle filling, capping and packaging. Proximity sensors, high speed counters and safety controls all working in fractions of a second. Try using a DDC controller for that!

In my industry of HVAC/R, the PLC system will function whether disconnected from the network or connected to a wired or wireless network. The PLC was invented to replace panels full of electro-mechanical relays, but has evolved into the most dynamic piece of control architecture in the automation industry. Control ranges from simple digital (on/off) control up to complicated analog PID control driving HVAC/R processes using ANY peripheral device operating at 0 - 5vdc, 0 - 10vdc, 4 - 20ma, resistance, RTD, etc. There are no proprieatary devices. Pull another controller off the the wall and replace it with a PLC and all wires and devices can be reused saving thousands of dollars in installation costs.

Know that in the automation industry, any manufacturer of DCS, DDC or PLC can be used to control a process. The question is, what system are you comfortable walking away from and sleeping at night without worries?