Installation guide

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The integral term
The integral term is an accumulation of RH error over time
multiplied by the integral gain. The way this works is as follows:
every ½ 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.
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VL3_IOM.pdf 71 11/19/2009 9:11:15 AM