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.

How to O2 analyzer works?

1 Answers  

WHAT IS THE Differance b/w on/off & pid control valve?

10 Answers  

What is the difference between PLC and DCS?

4 Answers   Honeywell,

What care will you take in the installation of control valves,SCADA,DCS and FOC in Oil and Gas Project?

0 Answers   KNPC,

any body please send me the old question papers of ongc test.

0 Answers   NTPC,

in which mode of the zener diode act when load voltage is approximately constant

1 Answers  

y v r connecting 250 ohms resistor in series when u cummunicate with BT in bench calibration?

5 Answers  

How 2 calibrate level tank having large height..?

2 Answers  

What is negative range in transmeter?

1 Answers   TCL,

What is three element drum level control system why its better than single element?

0 Answers  

whats the problem will arrise if we rotate the hosing screw of the differential pressure transmitter?

1 Answers  

During valve sizing from all calculation you got flow coefficient CV 12,than what it means? like for selecting pressure transmitter if your MAWP is 12 bar than you select a capsule of max. 20 bar which cover your mawp 12 in same way for selecting control valve If CV is 12 than how we use it in selecting valve??????

1 Answers