Symbol P
I
d
Display
P I d
Commercial Rice cooker
180
700
40
Electric kettle, 1.5 liter
95
80
20
NESCO 18 quart Roaster
250
900
230
Home use rice cooker,
54
60
15
Home use rice cooker, wine fermentation. (PD
mode) Switch set at Warm position
17
0
40
Slow cooker, 7 quart
180
700
40
Slow cooker, 4 quart
54
60
15
Slow cooker, PD mode (low overshoot)
40
0
40
Bradley Smoker
70
800
200
Table 1. Recommended PID parameters that can be used as reference point.
Please note that the P value in table is in Fahrenheit unit. If the controller is using
Celsius unit, divide the P value by 1.8. If you switch from Fahrenheit display to
Celsius, the controller will automatically convert all the settings.
6.1 Auto-Tune
The controller's most powerful feature is its ability to regulate virtually any cooker with
stable temperature control. For stable temperature control the controller requires two
things; (1) the controller must be set to the correct power level (see next section) and, (2)
that it must be
tuned
to the cooker being used. Tuning is the process that matches the
control characteristics of the controller to the heating characteristics of the cooker. The
controller is said to be tuned to the cooker when its memory is programmed with values
telling it how fast the cooker warms up, cools off, and how efficiently it transfers heat. For
example, consider the difference between a heat lamp and a hot plate. When electricity
is applied to a heat lamp it begins to heat instantaneously, and when it's turned off it
stops heating instantaneously. In contrast, a hot plate may take several minutes to begin
heating when electricity is applied and even longer to start cooling when electricity is
turned off. But, to do this it must be programmed with the time constants. Describing how
fast the heater heats when electricity is turned on and how fast it begins to cool when it's
turned off. These time constants are called the
tuning parameters.
.
Every type of cooker has its own unique set of tuning parameters. For the controller to
heat with stability, it must have programmed with the tuning parameters for the cooker
currently being used.
7
