Our lab has a FCS system: System 302 and Aimax-win,which I bought last year from Smar. Now I have some questions and ask for your help. By using Visual basic 6.0,I have designed a embeded control application programe based on dll provided by Aimax on the Aimax-win, and I want to achieve the ROUT and RCAS control mode for the PID function block in field device FI302, but I failed. why not, for that, perhaps I have to read or write the status of Rout.out or Rcas.out so as to bring the PID mode to Rcas or Rout. Am I right? but the DLL did not give me the means to read or write the status of any tag item. So, what should I do? Could you give me a help? I am looking forward to your help!

Sincerely!

 

I could not get what exactly you want to do. It seems that you have FCS which is similar to Yokogawa's Centum CS DCS. Is it ? You can try this by designing one switch which will put controller in ROUT or RCAS mode. When this switch is put in OFF (or whatever name you want to give), the controller has to switched to RCAS mode through sequence table (Tagname.mode.RCAS). You can do it through sequence table.

 

Thank you for your help! I think Centum CS is a DCS and FCS combined system. We can do something in the sequence table. But The FCS system here is System 302 by SMAR. And the HMI software is Aimax 4.2 by TA Cor.,in which we have no Control function blocks, nor sequence table. What I can do is the embeded control application programs based on the dynamic link library (DLL)provided by TA and VB6.0. But I can not put the PID block in the fieldbus device (FI302) in RCAS or ROUT mode. Can you help me further?

 

The OPC server that forms an integral part of SYSTEM302 permits you to write status to any read-write Fieldbus parameter with status. Note that not all Fieldbus parameters can be written, and that certain parameters can only be written in certain modes.

To bring data into the AIMAX software you need to include the status in your database just like you do with the value. From there on you should be able to access it. Alternatively your application can get the data from the SYSTEM302 OPC server directly without going through AIMAX.

Enough about the system, here is the explanation of the Fieldbus part which may be interesting for all readers:

Having done these basics, there are a few more things to consider. The FOUNDATION(tm) Fieldbus function block diagram language has a remote-cascade structure mechanism that comes into play to provide bumpless transfer initialization. This is explained in chapter 4 of the book mentioned below. To use the remote-cascade initialization:

1. Set the SHED_RCAS watchdog parameter in the resource block. During testing it may be a good idea to set it to 0 so that it is disabled.
2. Make sure your application always uses the "GoodCascade" quality bits when writing the RCAS_IN parameter
3. When the PID block is in Auto etc. it will set "NotInvited" substatus on the RCAS_OUT
4. When the operator changes the PID target mode to RCas the RCAS_OUT substatus will become "InitiailizationRequest" (IR)
5. When your application sees the IR substatus it should set "InitializationAcknowledge" (IA) on the RCAS_IN parameter of the PID. Without this handshake the mode will not change.
6. The PID actual mode should by now be in RCas, and the status on RCAS_OUT should be GoodCascade:NonSpecific
7. Now you can experiment with different values for

I.e. when you read/write the status your application needs to mask the bits for quality, limit condition, and substatus to interpret it correctly. This is explained in chapter 7 of the book mentioned below. Obviously your application must be able to do initialization for the mode transfer to be bumpless. When the application sees "IR" (step 5) it should use the associated value to do the back-calculation initialization.

The other way is to use hard mode transfer (without bumpless initialization):
1. Use GoodNonCascade quality for the RCAS_IN parameter.
2. When the operator changes the mode to RCas the PID block will accept this directly. In this case the "hard" way is the easy way. Make sure your process can tolerate process bumps if you use this method.

Any doubts, please contact me directly on the below address.

There is a lot to learn about the full capability of the Fieldbus function block diagram language and how to integrate it with third party applications. Take a look at the book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" (buy online in hardcopy or download immediately in softcopy). It is ideal for system integrators doing this kind of work. Chapter 4 (blocks) and 7 (OPC) are particularly applicable to your case. If your email does not support this hyperlink feature correctly, please copy the URL and paste it into your Internet browser. Mind the line wrap, make sure to get the complete path all the way to the 3036: <http://www.isa.org/Template.cfm?Section=Shop_ISA&Template=/Ecommerce/Product Display.cfm&ProductID=3036>

Jonas Berge
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[email protected]
www.smar.com