Real time and historical trend

What stamping time can I ask the DCS/PLC vendor for Real time trend and Historical trend of a DCS/PLC system having total 1300 I/Os? This is for Power plant application

Consultant given 10 seconds for Real time trend
and 30 sec for Historical trend

But I heared that, 100 msec also available

Analog inputs- 160
Analog Outputs- 40
Digital Inputs- 600
Digital outputs- 160
RTD inputs- 40
T/C inputs- 40

Ask not what is available, ask what is required.

If your processes and operations don't require data logging any more frequently than once a day, then do it once a day. If they need it once every millisecond then that's how often it has to be done. Then choose the method, system, equipment to meet that need.

Going from once every 10 secs to once every 100msecs is 100x more data. Will you really make use of it to benefit the process or operations?

Regards

Ken

I need the trend for Powerplant appication ,which is very important in fault analysis and data analysis. Can I ask the vendor for 100 msec stamping time for both real time and historical trends for at least some some variables (say 100 variables)?.

Group the signals based on the criticality & Rate of change log the data which has higer criticality & rate of change then log these data frequently may be 1 sec then these reqiures more space

Srik

Of course you can ask your vendor for 100mSec time-stamping. But what if he says "no, it can't be done". You're still left with a requirement. And presumably you now need to find some other way of fulfilling your requirement.

It's all a matter of defining the 'must have's and the 'nice to have's. Which category does the 100mSec data stamping fall in to?

Ken

100ms data will fill your harddrive really, really fast if you're intending to keep the historical data for very long. And you're asking for a lot of data to be recorded 10x/sec...

Instead of time-based data collection, you may really be better served by change-based data collection. I.e., record every time a binary signal changes, or record everytime an analog signal changes either by a percentage value or outside of a dead band (DO NOT record analog signals everytime they change - this will cause them to be recorded every PLC-scan because a change of even 1-bit in the word will cause the trigger)

What is the HMI/Data-Collection software package you're using? Some can do this, some can't.

You might check out this link

http://www.p1solutions.com/Prophecy.asp

Another constraint would be how fast the information from the sensor can actually be read. I've seen datalogs of 100,000+ samples a second. This was straight off of amps so that there was no delay for plc communications. Do you want counts or Engineering units? Again you will be delayed by scan times if you need EU. As said above you need to find your exact data collection needs (how fast and critical your process is) then you tell your vendor what to supply you. And if he can supply the sample speed it doesn't mean that the data is of any additional value.

anecdotal experiences:

OPC servers typically runs at 1 sec. update rates and internally do "update only on change outside a band".

The closest software package to a true historian that I worked with was Honeywell Plantscape Vista and it handled data at a max update rate of 1/sec, nothing faster.

Some paperless recorders handle rates higher/faster than 1/sec, but the data isn't realtime, it collected then block transferred.

I was told by a PI (enterprise historian) user that their max update rate was 1/sec.
I looked at Advantech's HMI software about 3 years ago for 1 sec updates on 150 channels and they couldn't guarantee 1/sec for T/Cs that needed linearization.

Ken's advice is the best you can possibly get!

Of course "everything" is critical. However, not everything is equally critical, and not everything is equally fast changing.

For example, lube system cooling water flow rate doesn't change very fast - 10 second updates may be sufficient to properly monitor that variable. Steam chest pressure may change rapidly, and you may want to monitor it every tenth of a second. Cooling tower discharge temperature changes slowly, and every 60 seconds may be more than adequate for monitoring it.