Answer / www.islamqa.com

# PLC is first invented and developed to be used with
discrete - on/off control & with small scale applications.

# DCS is designed and fabricated to handle modulating/PID
control applications & to serve in large scale I/Os
applications.

# with great progress and achievements in plc h/w and
networking technologies we have PID algorithms with PLC and
also plc become able to handle wide range of I/O'S like
DCS, actually with good engineering the one can build his
own DCS with multible PLCs.

# But actually with great engineering to build the DCS from
multible PLCs it will not be the same as pre-built/ready to
use DCS system in its functionality and its features.

# DCS is pre-fabricated system with compatible, integrated,
and tested H/W & S/W - has the following features:

- data collection & management.
- event and history management.
- instrument management.
- alarms management.
- smart and self diagnostics.
- advanced control strategy and easy to build, configure
control loops.
- redundancy.


Regards,

Ahmed Sabry
Control and Instrumentation Engineer
GPC - General Petroleum Company
ahmedsabry.online@gmail.com
CELL.: 00 2 0121367310

Answer / sajid

you are very correct..but u forgot one main thing..the scan
for PLC is lessthan DCS..
scan time for PLC is 100ms and scan time for DCS is 500 ms..
so that in indusrties they are using the PLC's for critical
operations along with DCS..such as shutdown or emergency
operations..

Regards..

SAJID
INSTRUMENTATION ENGINEER

Answer / ram

Difference between plc and dcs
using plc to control each tags one by one.
using dcs number tags can be control head a time

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