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VAPOR-LOGIC
®
VERSION 6 INSTALLATION AND OPERATION MANUAL
THE INTEGRAL TERM
The integral term is an accumulation of RH error over time multiplied by
the integral gain . Every 1/10 second when the demand is updated, the
instantaneous RH error (RH set point – actual RH) is added to a temporary
variable that accumulates the error . This accumulated error is multiplied by the
integral gain to create the integral term . The integral gain affects how fast the
humidifier corrects a droop condition . The higher the integral gain (Ki), the
faster the reaction . (An integral gain of zero disables this variable and allows
the unit to run on the proportional term only .)
With an integral gain term greater than zero and an actual humidity below set
point, the demand increases slightly with each update . If the actual humidity
is above set point, the demand decreases slightly . The amount it increases
or decreases depends on the magnitude of the RH error and the integral
gain value . The closer you are to the set point, the smaller the addition or
subtraction .
When looking at this control scheme, an interesting pattern occurs . The total
demand signal for the humidifier is the sum of the proportional part, the
integral part, and the derivative part . As the actual humidity approaches the
set point, the integral portion makes up the majority of the demand, and the
proportional part makes up very little . Once the set point is reached and the
unit stabilizes, the entire demand is made up of the integral part because the
proportional part is zero .
If the actual humidity goes over the set point, the integral term starts to
decrease . In addition, the proportional term becomes negative and actually
starts to subtract from the total system demand . These two terms work in
conjunction with each other to bring the humidifier back to set point .
PID tuning
OPERATION
