Posted by: Harold Ennulat | January 4, 2010

On Maintaining Control…. of a machine or process

No sooner do I title this blog “Harold In Control” then I find myself asking, “How much control do we actually exercise over a machine or process in a typical project?”

Certainly as a controls engineer we seek to gain enough control over a process to allow a machine or process to be operated in a reasonable manner. Some times this control is very basic when all that is required or desired is to just turn the machine on or off where perhaps only a single motor needs to be turned on and off. Some times this is very complex with many motors, sensors, operator controls, data inputs and outputs from recipe, maintenance, and MES systems required to properly control a machine or process to make some product.

Whether simple or complex, even a well defined control system can go out of control.  A motor could go bad where the line won’t start, or any of a myriad of things can go wrong causing loss of control. Typically, control is lost when some component breaks or exhibits a defect. In this case the defective part must be identified and replaced to regain control.

In other situations however, sometimes control can be lost when the process changes without adjusting the controls for an unexpected process change. Often these types of process changes are identified by the time commissioning is completed. This is often a time when the engineer gets to see how the operator really runs the machine or process. An example of this might be a flow control loop to fill and maintain a level in a coating pan, but the operator has figured out how to tap into the same line to draw a needed sample during production, sometimes causing the pan to go sufficiently empty to affect the product coating. Handling process upsets like this often requires special consideration and often some extra programming.

Why mention all this?  Maintaining control or staying in control is not a given once a machine or process is initially operational.  While a good design goes a long way to making the process operations reliable and of sufficient quality, a good maintenance program along with an eye for improvements to the process is also often needed as experience is gained with actually running the process.   This experience is often needed in order to improve or even to maintain an acceptable level of control over our operations.


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