Brief Notes on PID...
- PID is an acronym for Proptional
- Integral - Derivative. L.K. Enterprises' Kilntrol Digital
/ PC unit uses this method of temperature control. It is accomplished
by utilizing a temperature feedback mechanism and mathematical calculations
to give tight control over the output power levels going to the kiln in relation
to temperature set point levels.
- KDPC has initial settings for P-I-D of 10,
0, 0 respectively. However, using P at 10 with 0 for
I and D values will not give the best control over the
temperature, aspecially when in a HOLD temperature mode.
- Because each kiln has different time-temperature characteristics, the PID
values should ideally be tailored for each kiln. This may be a time-consuming
procedure, but once this is done for each individual kiln, the settings will
not need to be changed.
- The recomendation is to start with values for P-I-D of 10,
1, 1, and see how your kiln temperature tracks your profile ramp and
how steadily the temperature is held. These values (10-1-1)
should work adequately for MOST kilns.
- The "P" (Proportional) setting
controls power output in direct proportion to the difference in temperature
between the kiln and the set-point. The greater the value, the more "responsive"
to smaller temperature changes the power will be. However, just using "P"
(Proportional) control will cause some under and overshoot of the
temperature, so we need to somehow compensate. We do this be adding "I"
( Integral) and "D" (Derivative) control.
- The "I" (Integral) setting
senses when the kiln temperature is "not keeping up" to
the ramp set point, and gives the power a boost to help raise the temperature
quicker. A higher "I" value will cause it to respond
quicker, but be less stable, while a smaller value will cause it to respond
slower, but be more stable. However, using just "I"
will cause the kiln temperature to overshoot and oscillate above and below
the set point unless we anticipate when it is approaching the set point and
"slow" it down. This is what the "D"
control can do for us.
- The "D" (Derivative) setting
senses how quickly the temperature is approaching the set point and if it
is too fast, it tells the controller to reduce or increase power to the kiln
to help prevent overshoot or undershoot, depending on whether the kiln temperature
is increasing or decreasing with respect to the set point. In other words,
the "D" control setting anticipates what the control
ramp looks like in the future and compensates for what it interprets may result
in an over-shoot or under-shoot of the temperature. Thus by using all three
P, I and D feedback methods we may accomplish a much tighter
and more accurate degree of temperature control.
- KDPC software PID diagnostics mode.
If you wish to view the actual PID values as they are generated
by the controller, you may invoke a special diagnostics mode while the KDPC
program is running by simultaneously holding down the SHIFT + CTRL +
ALT keys and clicking with the LEFT mouse button on
the clear area below the TIME REMAINING display on the right
side of the window. This display may be toggled on and off with this key +
mouse click combination.
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