Answer / manikandan.d

PLC can control only one system at a time where as DCS can
control multisystem at a time DCS has its own database while
PLC does not. it has to use SCADA or MMI. scan time for PLC
is less than 10ms where as scan time for DCS is less than 100ms.

Answer / umashankar soni

PLC - is programmable logic controller
DCS - Distributed control system

The main difference between the two is there size i.e. in
market PLC is available in wide range of size from few IO's
to as large as you require,DCS is not.

PLC was earlier used to control sequential operation
only,whereas the DCS was for loop control.

Scanning time of PLC is very fast then that of DCS so where
the fast control is required the PLC is preffered as in
grid control system.

DCS comes with its graphis system where as in PLC
additional MMI softwere is require.

Answer / jose martin

Number input/output(Field tags) quantity can be used in DCS
are high.
but Plc it does not.

Answer / waqas

PLC is Programmable Logic Controller
DCS is Distributed Control System
PLC is just a monitoring/controlling device for a specific
application and it controls through its IO blocks.
DCS covers a wider aspect and it gathers information form
many PLCs and perform operations as per the Machine
Operator instructions.

Answer / naresh patil

PLC is control the any one system at time but DCS can
monitoring & control many system at a time.

Answer / bf chauhan

Basic difference is that PLC have 2 software for operation
one is SCADA Software and other is Programming software
while DCS has only one software which work as programming
as well as graphic building.

Also PLC mostly used where descrete IO are more and Analog
IOs are less while DCS are preferred where descrete IOs are
less and Analog IOs are more.ie. DCS is more suitable where
no. of closed loop are more.

Also DCS has have greater flexibility than the PLC.Analysis
of the process and report generation is better in DCS
compared to PLC.

Answer / vishal

PLC programmable logic controller
DCS distributed control system

Answer / mithilesh kumar

in plc if system is failed then plant tripped

but in dcs it never happen bcause in dcs redundancy is
available.if one system is failed then other system
recover.

scaning time of data it's totaly depends upon types.
ie data is analog or digital.

Answer / azad

The Main difference between PLC and DCS is SCAN CYCLE. PLC can able execute the instructions as one by one. whether DCS can make it as a page by page. So scanning time is reduced in DCS compare to PLCs.

Simply, If you have up to 10K I/O's you can go for PLC.
If You have more than that choose DCS.

Answer / ahmed

For understanding difference between plc and dcs watch this video.

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A PLC is programmed to drive three motors A, B and C as follows : After running motor A for an hour, motor B should get ON and motor A should get OFF. And after running motor B for an hour, motor C should get ON and motor B should get OFF. And after running motor C for an hour, motor A should get ON and motor C should get OFF. (That is, a cyclic repetition with time period one hour) Now, the second condition is: If any motor gone faulty and is tripped, the consecutive motor should get ON and the faulty (tripped) motor should be eliminated from cyclic repetition. The remaining two motors should bear the cyclic repetition of one hour each. (For healthy motor take logic as high and for tripped motor take logic as low) Now, the third condition is: When motor A load(Amps) exceeds 60% of its rated load, motor B should get ON in parallel to motor A. And when both motors A & B are running in parallel, and if their load exceeds 60% of their rated load, motor C should also start in parallel to A & B. [Here the cyclic repetition is eliminated, until their loads become normal(40%)] [Take logic high(1) for load at 60% and logic low(0) for load at 40%] Now draw a flow chart or a ladder diagram to fulfill the above condition.

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