Depending on the amount of water in the cooker, the performance may vary slightly. If
the temperature still overshoots too much, increase the P value. If the temperature
stabilizes one degree below the set point, reduce the P value.
Technical explanation
For people used to a conventional thermocouple or RTD sensor based PID controller,
they may think a PD controller can’t hold the temperature within one degree, because a
few degree temperature offset is needed for the controller to output enough power to
maintain stability. However, this is not true for a thermistor sensor based controller,
because a thermistor sensor is much more sensitive. A 0.3 degree offset is sufficient for
the controller sending enough power to maintain the temperature within one degree of
set point.
B) Proportional, Integral and Derivative (PID) mode.
The advantage of using the PID mode is fast action and no temperature offset (<1
degree) in long duration cooking. The disadvantage of PID mode is that there will be a
small temperature overshoot. Depending on the parameters used, the temperature may
oscillate several times before it settles to the set temperature. Because the very slow
response of the slow cooker, it is very difficult to not have any temperature overshoot
when PID mode is used. However, if you are making sous-vide and want to drop the food
pouches into the pot after temperature is close to the set point, this small temperature
overshoot actually will help the cooking and is preferred by many cooks. This is because
in most cases, the overshoot is not high enough and long enough to bring the food
temperature above the set point. It will help to bring the food temperature reach desired
temperature faster.
The following parameters worked well for our test.
Symbol P
I
d
C-F
Display
P I d C-F
Slow cooker, 4 quart
54
60
15
°F
Slow cooker, 4 quart
30
60
15
°C
Slow cooker, 7 quart
180
700
40
°F
Slow cooker, 7 quart
100
700
40
°C
It should be noted that these parameters are not optimized if the amount of water in the
pot is different. In general, weaker parameters (i.e., higher P and I) should be used when
a larger mass is heated (except that the derivative action should be lower). Larger mass
has larger heat inertia, so it needs to be moved more slowly to control. For the derivative
action, strong action will reduce the overshoot. In terms of long term temperature
precision, the difference in these parameters will have very little effect.
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