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

how bolometer is used in temperature measurement ??

1 Answers  

---

Can anybody tell me which type of question are asked in the interview for the FORMULATION(Pharma) as a instrumentation engineer, & question in building managment system.

0 Answers   Reddy Labs, ScienceWay,

---

i want to measure temp of hot sand(welding flux) in closed chamber(around 150 deg C).Which is better thermocouple or thermometer?

1 Answers  

---

units of pressure,flow, level,temperature? principle of pressure gauge? calibration of pressure tx., level tx., temperature tx.flow tx.? description of two wire ,three wire and four wire R.T.D.? WHAT IS INPUT AND OUTPUT OF TX.? WHAT IS INPUT AND OUTPUT OF R.T.D. AND THERMOCOUPLE? WHAT IS HOT LOOP AND COLD LOOP? WHAT IS INPUT AND OUT PUT AND OUTPUT OF D.C.S. AND P.L.C.? PRINCIPLE AND WORKING OF HART? WHAT IS PNP AND NPN PROXY? CALIBRATION OF PRESSURE ,LEVEL ,FLOW SWITCH? DESCRIPTION OF FIELDBUS FOUNDATION? WORKING OF SOV.?

2 Answers  

---

In thermocouple could we use the lug for termination or not,Thermocouple is any time,I am currently concerned with K type.please let me know if anybody know

4 Answers   Saudi Aramco Shell Refinery Company SASREF,

---

what is differnace between radar level tranmitter & hart type tranmitter?

3 Answers  

---

-200mmwc to 500mmwc range transmitter have there 4mA is -200 and 20mA is 500.what is the range in 12mA?

5 Answers   NCC,

---

pls tell me whethere flame proof HMI's are available or every HMI is manufactured by considering flame proof standard.

3 Answers  

---

which is the best type to measure level of a Tank(water). Displacer or Differential Pressure method?

2 Answers  

---

Before erect the instrument what should you do?

3 Answers   L&T,

---

Which types of quections asked in interview for FORMULATION PLANT (PHARMA)

0 Answers  

---

why we use the ac supply load cell>?can we use the dc supply load cell?advantages and disadvantage of the ac supply load cell?

0 Answers  

---