We use Invensys Connoisseur APC to optimize our process. When we migrated our DCS from Honeywell TDC3000 to Experion, we converted the CL (for DCS logic control of PID loop) to SCM. The problem is that ever since the upgrading, we were having difficulty in putting APC on closed loop (as it takes some time for the SCM to complete the whole checking of the logic - especially on all MV's whereas in CL it is very fast).

Can anybody help me on this or have similar situation?

TQ

 

Assuming the SCM manipulates the right parameters in the right way and can actually put the APC scheme on closed loop have you considered putting the checking of the MVs into a CM which is executed at a reasonably fast rate, enabled at the correct step in the SCM logic and the resulting derived logic status checked by an SCM transition?

Dave MH.

 

Dear DaveMH,
It is already in CM (in this case C300). However, the way the SCM is structured is such that it will check all parameters for each MV in one looping (through instances). Once that particular MV has finished, then it will be followed by the next MV and so on. It will take ~ 10 sec for each MV to complete the whole SCM before starting it again, whereas in CL looping is done to check the whole MV's at one go for each parameters and then to next parameters for all MV's. The question is, is it possible to do looping in SCM like in CL.

TQ.

Rgds

 

Dear Kuman,

I am not sure we have understood each other so bear with me for a moment.

My understanding is that it is not easy to replicate a true loop like CL in an SCM although I may be out of date here.

The CM I was referring to was not the processor but the software Control Module used for the Function Block programming side of Experion as oppose to the SCM. Depending upon the parameters it is required to test you could take the checks out of the SCM and program the logic using FBs in a CM (ANDs, ORs etc.) to come up with a total pass/fail condition at that step in the sequence. Then just check the pass/fail condition at the appropriate transition in the SCM.

It may not be an elegant solution but it should be quicker than iterating through an SCM several times. You might need to play around with the data types (type conversion, enumerations) of the parameter comparisons I remember having "fun" doing this but there's usually something you can use. You may want to schedule the CM(s?) and I/O to run quicker and before the SCM and enable the checks only at a particular point in the sequence.

Hope that's clear. If I have misunderstood my apologies.

DaveMH

 

Here are sme tips that may speed up your SCM process:

1) Set Step MINTIME to zero if it is not already.

2) Set Step Sequential Order to None, it maybe set to ALLOUTPUTS.

3) Make use of the SYNCH block to run up to 10 parallel paths of steps and transitions, thus significantly reducing your time to accomplish all your MV manipulations.

4) Run the SCM at a faster scan rate, this may not help if the CM's that contain your MV's are running at a slower scan rate.

Otherwise you could do some of the manipulation within the CM and not use a SCM. For instance you could monitor a OPC flag set by Conisour, once the APC application goes online, than the flag will trigger changes in the MV, such as placing it in CASCADE mode.

 

Dear MH and Marc,

Thanks for the info. I'm not a DCS/Automation Engineer. I'm still learning on the new DCS system. I will try the suggestions and let you guys know the outcome. Probably with some more questions,

Rgds.

 

Hopefully you did not experience same problem when migrating MVAC application to Experion !

Jean-Marc & Joel

 

If I understand it well you are trying to migrate a CL application that uses loops iterated multiple times in the same cycle. I've seen some very good tips here to optimize this in a C300 but there is no possibility to do exactly the same on that platform. Note that you could not do it in an xPM either, because of pre-emption points, until a certain release.

Yes, you can do all calculations in CMs and yes you can use parallel execution in the SCM and combine both. If you put enough function block in place you can even be done in 1 cycle.

If you accomplish your goals with that, it's perfect. If you still want to do loops as you did before I think you'll need an ACE node and use the CAB (custom algorithm block) functionality.

 

What Rudy recommended...Should have used CAB but if you already converted to SCM then perhaps try to optimize it.