Open-loop Process Identification
1. Stabilize the process either manually or automatically.

2. Set the controller to manual mode (if the controller is still running under auto mode).

3. Record the initial value of the controller's output.

4. Mark a starting position. A starting position must be several second a head.

5. When the recorder's pen reaches the starting point, make a bump at the controller's output of about 5 to 20%. 
6. Record the final value of the controller's output.
7. Stop the test  when ample of response curve is recorded. 

8. Return the process back to operating condition. 


Further reading on open-loop process identification is available at:

1. Thomas B. Kinney, Tuning Process Controllers, Chemical Engineering, 19 Sept. 83, pp 19-20
2. Bob Connel, Process Instrumentation Applications Manual, McGraw-Hill Book Co., 1996, pp 212-213

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