Relay feedback in heat-only applications

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I am tuning a PID controller using the relay feedback method to obtain approximations for the ultimate gain (Ku) and the ultimate period (Pu). This is working well for heat/cool applications. However, for heat only applications it fails. Since there is no cool power, the cooling slope stays constant, making the cycle period variable based on the input power amplitude. I think this makes it invalid to use this technique for heat (or cool) only processes. Can anyone confirm or deny this, and if so, provide some clarification here?

-- Jeff Vinnacombe (jeffrey62@mybluelight.com), October 04, 2002

Answers

idiotic ====stuupiiid------senseless idiot=====SHUT U R!!!!!!

-- arvind (arvind_it53@yahoo.com), September 27, 2003.

i conform that, for hear and cool application Relay Feedback test will work, but not for only cool or heat application. Ph.D student

-- Andy srinivasan (itzsrini@yahoo.co.in), January 30, 2004.

Iíve been seeing the same thing in my application. Iím trying to heat a brass bar up to a constant temperature; the bar is well insulated, so the process is very asymmetric. Does anyone know of a good information source that deals with this type of system? Thanks in advance.

-- tom s (oysterhead978@yahoo.com), October 15, 2004.

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