Answer / carl_ellis

Question:
Controller not working in auto mode?...what are the problem can occur...Pls explain

Answer:
If a controller is not in automatic mode it is either broken or in manual mode.

In manual mode the controller's output is fixed at some percentage output and the controller is not adjusting its output to maintain the setpoint (SP).

While running at a fixed output, the process's process variable (PV) will generally stabilize at some value above or below the setpoint. PV changes will be dependent on external influences, like load changes.

However, if the output reaches an extreme, like 100% or 0%, the process can be put in jeopardy of going into a hazardous state from the uncontrolled input into the process or removal from the process of energy or mass, whatever the controller is controlling. Presumably, safeties are in place to shutdown the process should those dangerous conditions result from manual mode.

Carl Ellis
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