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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.

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Operation

DriSteem Vapor-logic 4 User Manual

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