1. Clear details of split range control.
2. When & how it is implemented in process industry.
3. Please help me how the two valves are calibrated from one controller output.

 

I have seen the examples in the gas conditioning skids for Gas Turbines and in PRDS having HP, MP and LP skids.

For gas conditioning skids the pressure transmitters controls two valves in parallel one with low capacity and other with high capacity. During normal operation of the GT for slight fluctuations in the pressure the low capacity valve operates say 0-100% opening for 3-9 psi o/p from current to pneumatic transducer. And when the large fluctuations in the pressure are there in case of large fluctuations of gas flow (due to sudden large load demands and load shedding) by Gas Turbine the high capacity valve operates say 0-100% opening for 9-15 psi o/p from Current to pneumatic transducer. Similarly split range can also be applied to PRDS system where one valve can be dumping steam to MP header from HP header and other can be used for venting the header if the pressure goes beyond the SP. It can also be used for level applications on level low the make up valve to a tank can increase o/p to control the level, but if still the level is low a recirculation valve can also increase the o/p to control the level by means of recirculation.

Normally the valves are calibrated through positioners for the split range action. It also depends upon the type of positioner used and varies from model to model.

Regards,
NIKH

 

Here are some vendor-authored articles and non-commercial white papers we've published on the subject of split range control for your use:

Split range control methods (http://www.controlglobal.com/articles/205/580.html)
Process control authority Bela Liptak brings in specialists from his cadre of co-authors to answer a reader's question. Find out which books and online courses they...

Split-Ranging Multiple Valves (http://www.controlglobal.com/articles/114.html)
Readers Write In and Question Split-Range Concept

Predictive Control of Batch Reactors
(http://www.controlglobal.com/whitepapers/2008/114.html)
Continuous control of batch reactors is now feasible with Model Based
Predictive Control. First Principles modeling allows the solution of
difficult problems of non...

Implementing MPC to reduce variability by optimizing control valve response
(http://www.controlglobal.com/whitepapers/2005/042.html)
In this paper, a model predictive controller is configured to simultaneously manipulate a small valve and a large valve, eliminating the problems inherent in...

Gas Blanketing Controls and How to Contribute to IEH v.5
(http://www.controlglobal.com/articles/GasBlanketingControls0812.html)
A Process Engineer Has Concerns About the Standard Split-Range Nitrogen Blanketing on a Vessel Done with a DCS PID Controller with Separate Analog Outputs to Each...

Model-predictive control can solve valve problem
(http://www.controlglobal.com/articles/2005/533.html)
CONTROL columnist Greg McMillan addresses the use of fine adjustment valves to reduce process variability and suggests that now is a fine time to break away from old...

Split personality (http://www.controlglobal.com/articles/2005/283.html
Pressure Gauges: This month's Control Talk proves a real pressure test for readers of CONTROL. Columnists Greg McMillan and Stan Weiner provide answers and the...

How to select control valves, Part 3
(http://www.controlglobal.com/articles/2006/215.html
When it comes to selecting and sizing control valves, gain and stability are key characteristics. The non-commercial valve selection chart in this article serves as...