Head Temperature Oscillating

Printing last night with the head set to 190degrees I noted on the web interface that the temperature was tracing a perfect sine wave between 181 and 193degrees and it stay like this for the duration of the print. Tried again this morning and it was very stable at 200degrees for the first layer and then started oscillating again when the temperature reduced to 190degrees.
I increased the temperature to 200 and it again was very stable. Changed the temperature several times to check the amplitude of the change at 200 and 190 and on my third change to 190 it stabalised after a few cycles and the fluctuations were less than half a degree remaining stable for the remainder of the print. Not the first time I've seen these oscillations.
Any suggestions?
John

It sounds as though the PID parameters need adjusting. The firmware doesn't yet implement the M130 to M133 commands that allow them to be changed, but I could add them if you would be interested in trying different PID parameters.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
It sounds as though the PID parameters need adjusting. The firmware doesn't yet implement the M130 to M133 commands that allow them to be changed, but I could add them if you would be interested in trying different PID parameters.

Sure, more than happy to try out just as soon as soon as I have worked out what the PID parameters are.
John

Quote
johneato
... just as soon as soon as I have worked out what the PID parameters are.confused smiley

PID stands for a "type of controll system" wikipedia has a very nice article.
PID tuning is somtimes regarded as "hard". I myself have struggeld for hours where an expert could set the correct parameters very quickly (for a motor contorller).

Thanks for the PID explanation, I now understand.
I have been printing ABS today and so decided to investigate a bit more with this and seems that any temperature 200C and above is very stable anything below tends to oscillate by about 12C.
John