What is the difference between PLC and DCS?
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First let's take a quick brief history about controllers:
1 - For analog control loops we have a stand alone PID controller.
2 - Then we get a networked PID controllers through a hub and HMI for configuring and monitoring.
The PID itself contain a network port.
SIEMENS introduced PID 353 & PROCIDIA software for it.
3 - Then we get DDC - DIRECT DIGITAL CONTROL, single CPU, I/O'S for analog instruments only & networked PC is an option.
SIEMENS introduced APOGEE, FISHER introduced ROC.
has disadv. of system halting/failure.
4 - The next phase is DCS - Distributed Control System, and this is first introduced by HONEYWELL & YOKOGAWA.
Ability for handling large scale of I/O'S, discrete and analog, complex control loops, PID algorithms calculations and executions.
5 - PLC is basically designed and produced for discrete on/off control, limited I/O'S.
but modern PLC with great progress in h/w technology introduced itself as a less expensive option for PID, with it's complicated calculations and algorithms.
6 - by the time with great achievements in H/W tech. and networking capabilities the single PLC can handle discrete and analog instruments with wide range.
7 - Now the man can make his own DCS with multible networked PLC'S, but it will need a great engineering and effortsto get near from DCS features and functionality.
Regards,
Ahmed Sabry
Control and Instrumentation Engineer
GPC - General Petroleum Company
ahmedsabry.online@gmail.com
CELL.: 00 2 0121367310
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