Armstrong World Industries 6100 - Manual (Page 43)

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PID Control
PID control is essential on the HumidiClean series for maintaining the desired relative humidity (RH)
by adjusting the humidifiers output. Please note that the PID control is only used when a RH sensor is
supplying the demand in place of a humidistat (configured in Operation Setup Menu). The PID Settings
will control how the demand is adjusted according to the error between the current RH and the desired
RH set point. There are four variables of the PID control that can be adjusted to customize the way
your HumidiClean reacts to a demand signal.
Proportional Band (PB) – The proportional band value determines how your humidifier will react to
the current error (desired – current). Smaller PB values will take longer for your unit to reach its RH set
point. Larger PB values will quickly reach their RH set points but possibly result in demand instability
(demand bounces between on and off). The default PB value on the HumidiClean is 15.
Integral Reset Value (IRV) – The integral reset value determines how your humidifier will react to the
sum of the amount of error in the past. By decreasing the IRV, you will have less overshoot after you
reach your RH set point, but increase the amount of time it takes to reach the set point. Increasing
your IRV will allow you to quickly achieve your RH set point and reach a steady demand, but will have
higher RH overshoot in the process. The default IRV value on the HumidiClean is 125.
Derivative Gain (DG) – The derivative gain value determines how much your demand will be affected
by the past rate of change of error on your HumidiClean. Larger DG values will improve the demand
stability and decrease RH overshoot near the RH set point. However, larger DG values can also
amplify any noise in the demand signal between the controller and the HumidiClean, giving the unit an
unstable demand. The default DG value on the HumidiClean is 0.
SI Interval (SI) – The SI interval value controls how much data from the past is used for calculating
the integral term and derivative term. The SI interval value is in seconds, so the default SI integral
value of 10 means 10 seconds of past error data is used when calculating the integral and derivative
terms.
Shortcuts to tuning your PID values – If your HumidiClean:
- is not reaching its desired RH quick enough, increase the proportional band (PB) value or
integral reset value (IRV) slowly until acceptable rate is reached. Increasing both of these values
will help you reach your desired RH value quicker. Caution, increasing your PB value too high can
create an unstable demand scenario when your demand will bounce between having a demand
and zero, causing your contactor to pull in and out constantly. Avoid this by slowly increasing your
PB value in increments as to not raise it too high. Increasing your IRV value too high will result
in higher overshoot, causing your %RH to rise above the desired %RH (higher IRV values create
higher overshoot).
- has too high of an overshoot, decrease the integral reset value (IRV) or increase the derivative
gain (DG) slowly until acceptable overshoot is found. Decreasing the IRV will decrease your
overshoot, but it will also increase the time it takes for your humidifier to reach its desired RH.
Increasing your DG value will help improve demand stability (reaching a constant demand value)
and decrease set point overshoot, but could amplify any signal noise (if there is any) coming from
your RH sensor. Amplifying signal noise could create an unstable demand and create a false
demand (humidifying when there is no need).