Answer / abhishek

Main difference between DCS and PLC is about the scanning
time. PLC's have a fixed scanning time whereas DCS
execuation order(scanning) can be varied with certain
minimum limit. Generally a PLC can have a scan rate of as
low as 5msec(fixed) to some where around 20msec(fixed). As
DCS handles larger number of inputs/outputs its scanning
rate is 50msec and this value needs to be defined (can be
kept more than 50msec) while writing a program. But latest
DCS can have scanning rate of 20msec.

Answer / vijay

Scan time is time required for checking i/p,to executive
program and give out put.generally 5msecfor plc

Answer / raja2016

time taken for 1 scan sequence ::

Housekeeping -I/P update - Program execution - O/P update - Programmer windows - System communication window - Housekeeping

Answer / abu maryam

scanning time:
In general: scanning time: it is the time taken to read all inputs then execute the program and apply on outputs.
In PLC: it is only 1 processor check the previous procedures so its scan time depend on the quantity of data and program.
In DCS: There are several processors each processor has its inputs and outputs and its private program so each processor in DCS has its private scan time applied on each loop.

Answer / srikrishnan

SCANNING TIME OF PLC DEPENDS ON THE NUMBER OF RUNGS, JUMP
COMMANDS, SUB ROUTINES, AND INTERFACING DRIVER
CONFIGURATION. THERE IS NO FIXED SCAN TIME FOR PLC.

why we use the 4-20 mamp signal used for transmitter.

5 Answers   Tecnimont,

why do 4 mA serves as 0% not 0 mA?

10 Answers  

there is one orifice plate already installed on 3" line, but my previous engineer(who is not working here) removed that tx, but now i want to take it in to the process, so now what i have to do now? flow fluid is hytherm oil of temp. 260deg & pressure is 3bar.

2 Answers  

How to consider the flow directions for control valve (Globe) Is the there any easy understanding in order to select the flow directions?

3 Answers  

what do you mean by Loop checking ? What are the cold loop check and hot loop check? what are the difference between these two loops?

1 Answers  

wht is snap action switch?where it is used?is there any diff between snap action switch and normal pressure switch?

1 Answers   ONGC,

how pressure transmitter work, what is its principal to measure and how its generate signal. for pressure transmitterinstallation which precautions must be taken ??

0 Answers  

How addressable fire systems work? Pl. send details with architect.(Loop), also send details regarding Gas system. Pl. help me.Thanks

0 Answers   Siemens,

Can anyone send most commonley asked Instrumentation questions and answers in cement industry please?

0 Answers  

how to calibrate the interface leveltrol

1 Answers   Lanco,

how we will install a positioner ?

2 Answers   Descon,

Difference HAZOP and HIRA

1 Answers