Figure 24: The Effect Of Changing The Proportional Gain - Hydronix Hydro-Control VI Operator's Manual

Using Moisture Control
If required it is possible to calibrate the recipe to display a real moisture value. The same
sequence as for CALC Mode should be used (see section 2.8 above). After entering the
calibration data the Recipe will default to CALC Mode and should be set to Auto Mode.
Optimising
3.3
Different installations will mix the water in at different rates and therefore the AUTO Mode
parameters may need to be adjusted to optimise the speed and accuracy of the water addition.
The AUTO Mode water addition is adjusted using 3 AUTO Mode parameters, Proportional Gain,
Integral Gain and Derivative Gain. Normally these parameters are set globally for all recipes
using the values in the System Parameters pages, but these can be over-ridden for individual
recipes if necessary.
For most applications, it is only necessary to change the Proportional Gain, and there is an
option on the recipe selection screen to do this easily without having to go to the recipe editor.
The Integral and Derivative Gains are disabled by setting their values to zero.
In order to optimise the AUTO Mode, it is necessary to run a number of batches whilst
increasing the Proportional Gain value to a point where it just overshoots the target value, then
reduce the gain value so that it stops overshooting the target, and this gives the optimal value
for the Proportional Gain parameter.
If during the water addition phase the moisture value approaches the target but is not able to
reach it then this may be due to insufficient water being added each time the valves are pulsed.
The Integral Gain should be increased with an associated reduction in Proportional Gain to
prevent overshoot in the initial stages of the water addition.
If the coarse valve is not on long enough during the water addition, increasing the Derivative
Gain whilst decreasing the Proportional Gain will allow the coarse valve to be on for longer in
the initial stages without ultimately overshooting the target.
The Minus Tolerance in the recipe parameters is used as a deadband and when the moisture
value reaches this offset from the target the target is deemed to have been reached.
Moisture
Target

Figure 24: The effect of changing the Proportional Gain

As can be seen from Figure 24, if the Proportional Gain is set too high then the moisture will
overshoot the target value. If the Proportional Gain is set too low then the water is added to
slowly and the moisture will take too long to get to the target value.
50 Hydro-Control VI Operators Guide HD0456 Rev 1.7.1
Chapter 8
Too High
Correct
Too Low
Time