Future Design MCTB 4.3, Руководство пользователя

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MCTB
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Once the process has stabilized, if the process value is lower than the set point by 5° for example, and 20.0 is
used for the proportional band, that is equal to an offset of 25%. Thus, the PB offset would be increased by
25% to compensate for the set point offset in the process. Note that automatic tune is disabled for P or PD
control. In order to perform an auto tune, the integral time would have to be set to a value greater than zero.
P or PD control is not precise for processes with changing load conditions and will require frequent adjustments
of the offset. The PID control mode should be used because it automatically does this.
9.1.2 Heat/Cool (Bimodal) Control
When a loop is programmed for heat/cool operation, the values of the Cooling PB and Dead Band affect the
way the heat and cool outputs work together to control the process.
The Cooling PB is measured in % of the proportional band with a range 50-300. Set cooling PB to 100% to
begin and examine the cooling effect. If cooling action should be enhanced then decrease the cooling band. If
cooling action is too strong then increase the cooling band. The value of the cooling proportional band is related
to the heating proportional band and its value remains unchanged throughout any auto tuning procedures.
NOTE:
The adjustment of the Cooling PB is also related to the cooling media used. When air is used as the
cooling media, it is recommended that the Cooling PB be set to 100%. For oil, a typical setting to use
for the Cooling PB is 125%. If water is used as the cooling media then adjust the Cooling PB to 250%.
The adjustment of
Dead Band is more dependent upon system requirements. If more positive values of dead
band (greater dead band) are used, an unwanted cooling action can be avoided but an excessive overshoot
may occur. If more negative values of dead band (greater overlap) are used, an excessive overshoot can be
minimized but an unwanted cooling action may occur.
Dead band is adjustable in the range of -36.0% to 36.0 % of the heating proportional band. A negative dead
band value provides an overlap between heating and cooling action in which both outputs can be active at the
same time. A positive dead band value provides a dead band area in which neither output is active around set
point.
9.1.3 Configuring PID Sets
The PID Set screen allows the user to assign multiple PID sets to the control loop. Each loop can have up to
five PID sets assigned. The default is one PID set. When only one PID set is assigned, the PID entries and
activation set point fields are hidden. At least two PID sets must be enabled in order to enter specific PID
values and the process value at which they will be used.
The
Number of Active PID Sets allows the user to specify how many PID sets to use. When set to a value of
one, only the PID values currently set to the loop are used (the values displayed on the Tuning screen). When