Hi,

I am trying to figure out the principles of S88.01 Standard. I have read ISA book Applying S88 Batch Control From a user perspective written by Jim Parshall and Larry Lamb. Well this book is pretty useful. I have developed DCS software for continuous process control , but unfortunately I have no experience in Batch process using S88.01.

Afte reading the book, the following questions remain unanswered to me. I am sure the experts in this form can help me out:
1) How and where the process cell is implemented. Is it in DCS Controlls or in HMI/SCDA?

2) The process cell has Basic controls, procedural controls and co-ordination controls. As I understand the basic controls (regulatory controls like continous controls) are implementd in DCS controls, procedural controls and co-ordinated controls are implemented in SCADA/HMI. Am I correct?

3) I understand control module is the lowest level physical model. This module resides in SCADA/HMI, instruc a phase logic residing in DCS/PLC to control the device. Am I correct?

Prasanna

 

In answer to your questions:
The S88 standard is a little "woolly" regarding the Physical Model. This can be interpreted in several ways, this is only my own...

1) Usually the process cell lives in the DCS and is a container for the units of plant equipment typically a folder on the plant hierarchy of your DCS.

2)& 3) Again this is platform dependant. S88 is not mandatory but rather a guide, however, depending upon the size of your system the DCS can contain the unit operations, phases, cells, units, equipment modules and control modules. The master recipe may be held in a PC controlling the batch, which then copies it to a control recipe for a batch that is about to execute. This will then execute unit procedures passing control to the DCS to execute each unit op of the procedure. The unit operations, typically SFC’s, consists of phases which then instruct the equipment modules which control modules to operate etc.

Obviously the split between where the demarcation in control takes place is not important, but more the principle of how the models interact. One thing to be wary of is exception handling within the physical model that S88 skims over and there are a number of techniques you can use during the design stages rather than later.

Again, these are only my thoughts, others may disagree.

Oldie
[email protected] remove nospam

 

On August 22, 2003, Namitha wrote:
> 1) How and where the process cell is implemented. Is it in DCS Controlls or in HMI/SCADA? <

For implementing Process Cell you need an other software (Example: TP Batch from Honeywell or RS Batch from Rockwell).

> 2) The process cell has Basic controls, procedural controls and co-ordination controls. As I understand the basic controls (regulatory controls like continous controls) are implementd in DCS controls, procedural controls and co-ordinated controls are implemented in SCADA/HMI. Am I correct? <

No, Procedural controls are part of the DCS too.

> 3) I understand control module is the lowest level physical model. This module resides in SCADA/HMI, instruc a phase logic residing in DCS/PLC to control the device. Am I correct? <

Usually, Control module and Equipment module resides in the PLC or DCS, Unit, Process Cell resides in the Batching software. The HMI/Scada is used only for Viewing and manual control of control module.

 

S88.01 defines the basic structure of batch control. Most DCS suppliers have S88 conforming batch control software for their own DCS that often runs in a separate network-connected controller, but sometimes may run on the multifunction controllers as well. There are also batch control software packages offered by the independent HMI suppliers that operate in the HMI network environment. Most of the PLC suppliers also offer S88 conforming batch control packages as well.

Selection of the "best" S88 batch control software depends on the nature of the process you are controlling. If the batching is incidental to a process requiring a DCS for continuous control, then the DCS suppliers batch software is probably best. If the process is highly discrete and requires a PLC to control switching actions, and you are using the same PLC suppliers HMI software, then by all means, use their batch software as well. If the process is PLC controlled with some continuous control, and you have the ability or contract the system integration, then often the batch solutions from an independent HMI supplier are best.

S88 only offers a common architecture for the batch control software so that you know each supplier is talking about the same thing when they describe their recipe builder and phase logic programming methods, for example. Talk with the suppliers.

Dick Caro
============================================
Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +1.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected]
Web: http://www.CMC.us
============================================

 

Prasanna

1 The process cell is usually the domain that is covered by a batch manager, in many ways it hardly exists in the DCS as specific entity. A DCS may well cover several.

2 >basic controls (regulatory controls like continuous controls) are
implemented in DCS controls>

Yes generally, although some may be in packages outside the DCS, and of course it might be a PLC not a DCS.

>procedural controls and co-ordinated controls are implemented in
SCADA/HMI>

Not really. Some procedural control (typically phases, but it can be Operations or Unit procedures (or sometimes whole recipe procedures) is programmed in the DCS.

3 <control module is the lowest level physical model. This module resides in
SCADA/HMI>

It is usually an entity (eg a valve driver) that is programmed in the controllers and is also linked to the corresponding tag in the HMI. It is a state setter and watcher. Some can be quite complex, such as cascade loops
or a parent of a group of CMs. For example a double block and bleed module containing three valve modules. Control Modules can also do things like exception handling.

>instruc a phase logic residing in DCS/PLC to control the device. Am I
correct?>

The phase logic generally tells the control modules what to do.

Some applications use commercial Batch managers (eg RSBatch, InBatch, DeltaV batch etc) others people roll their own in the SCADA. Batch managers (sort of) handle co-ordination control. They interface with the procedural control in the DCS/PLC via a phase logic interface that implements a standard state transition model, typically (and unfortunately) taken verbatim from Figure 18 - State transition diagram for example states for procedural elements in the standard. Unfortunately suppliers ignored the word Example.

Regards,
Francis Lovering
www.controldraw.co.uk