1) What is the scan time of

i) DCS
ii) PLS
iii) SCADA system

2) How to check the SCAN time practically for

i) DCS
ii) PLS
iii) SCADA system

3) What is controller loading?

4) How controller loading affects the scan time of DCS?

5) If controller loading affects the scan time then SOE module who has scan time of 3ms solve the purpose of critical process control?

6) How SOE modules works? do they have separate watch dog & if yes then do they communicate with MAin watch dog of DCS & help in Control?

7) by using SOE module can we reduce the scan time of DCS? how?

 

SCAN period in PLC and DCS are fundamentally different.

PLC: it is the time taken to scan & process the entire logic.

DCS: it is the time in which the processor is supposed to complete scanning & processing.

SCADA/HMI: it is the time interval at which the software polls the processor for its data updates.

further details on how to view the scan periods is product/system specific.

let me know which system u are referring to.

Regards
SPR

 

For other questions:

3. CONTROLLER LOADING: PLC controller loading is with respect to your requirements on I/Os or scan time. You cannot go beyond XYZ no. of I/Os or say your process cannot tolerate a scan time > ABC msec. So that defines your loading on PLC

DCS: LOADING OF PROCESSOR IS A WIDER CONCEPT IN DCS THAN THAT IN PLC. IT CAN BE BROADLY CATEGORISED IN TERMS OF COMMUNICATIONS, PROCESSING AND MEMORY. the processor is supposed to complete the scanning, processing & updating the I/Os in a fix time interval. If due to any reason, the processor is unable to complete its job in that time, it announces processor over-runs (meaning, the processor is working overtime) and the next scan cycle gets delayed by equal amount of time. Hence, your loading in DCS is decided by the complexity of the control logic, no. of tags, no. of I/Os, peer to peer commnunication between different tags etc.
CONTROLLER LOADING IS A BROAD TERM.

4. If your DCS is loaded, the controller alarms overruns and the consecutive scan cycles are delayed. They keep accumulating and can cause havoc in a critical process plant like refining/petrochemical/fertilizer etc.

5. SOE is NOT USED FOR CONTROL. It is used for data collection in terms of events only. SOE in DCS requires an additional module and a separate software. Again vendor specific. Which r u referring?

6. SOE modules in DCS scan the hardwired I/Os at 1 ms (or whatever interval). The module maintains its own scanning and is time-synchronised with the controller, because SOE modules time-stamp the events captured. Hence the events captured by SOE are updated on controller and sent to the HMI. Basically used for analysis during a plant trip, as to which event occurred first.

7. NO RELATION in scan time of DCS and SOE. Distributed control itself is a very self explanatory term. There are different processors in a controller that handle control processing and communications processing. Here in case of SOE, the communications processor works and control processor has no job in SOE collection.

Understanding DCS requires extensive study and experience.

Regards
SPR