In a continuous process plant what is the time span a dcs can control the plant without any manual operations or supervisory acts?? One of my friend is working is a power plant and says there dcs cant control the plant more than 15mins without any operator. They have to watch the process every time. But when any process is automated i think its made to have max control by its controller and control the process for long times without any manual or supervisory action other than in some critical failure conditions.

In numerous plants that I have programmed, the plant operates for extended periods of time with no operator action, some of them have no onsite shifts during the weekend, with an automated callout should something happen to go wrong.

Vijayant, The ultimate goal in automation is to require no operator input. Unfortunately, the reality is money. Is a company willing to invest a million dollars to install a system that replaces on worker? Quite often, in my experience, it is much more effective to hire a human to preform the complex decision making that could be accomplished using automation, but at a drastically lower cost.

Another consideration would be the age of the plant under consideration. Is it 20 or 30 years old, using controls from that era, or just now being designed.

An other question to ask is "What if no one is there to push the Estop", or "what is the worst that can happen?" A power plant is a rather complected collection of systems that could have dire results it something not planned for goes wrong.

Whenever I am asked by a supervisor if something can be done (such as the unattended plant operation in your original question), my standard answer is "Yes. How money do you have to spend on it?"

Yes I agree with Thomas Stevic. For automation, the limitation is only imagination and investment.
But manual intervention is a must, when the plant is operated " OFF DESIGN" conditions and proper maintenance and upgrades are not done.

Thank you for comments. I too agree with you Mr. Stevic aging and cost are always considered. Manual intervention is must but if a plant cant run a day without any manual action then it also genarates cost that can be reduced by a good automation. Is it true..