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ACS Minima userguide version 1.6 April 19.doc
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M
INIMA OWNERS MANUAL
PID Values Explained
Proportional control
applies power to the heating elements in proportion to how far you are from the set point.
Its main drawback is that the closer you get to the set point, the power it applies (it's why we don't use it on the
service boiler). Eventually it doesn’t push hard enough to change the temperature and the brew boiler can run
continuously close to the set-point temperature, but not quite there.
Integral control
tries to even out the difference of the time spent above and below the set point brew
temperature. If you’ve set 93C as your set point and spent a minute running at below it will try to push you over to
93C for similar amount of time. This action compensates for P’s inability to make that last effort.
This would seem to be enough, but to allow the brew boiler to recover rapidly but not overshoot the set-point
temperature excessively, welcome to the
derivative control
.
Derivative as a brake or dampener
on how much power the
Proportional control
uses. The more it tries to
change the value, the more it counteracts the effort…it's why it's sometimes called
"Rate".
Measures change
over speed. It will reduce the effects of P and I more, the faster the set point is approached. Low values of D can
cause overshoots; high values of D can make response sluggish.
We recommend you use the values in the guide, but
with experience,
small changes may benefit the operation
of the Minima in its specific environment because this may be hotter or cooler than the test environment.
Warning, if you accidentally power on the machine whilst holding only the right hand button,
this will reset the control system to Gicar factory settings and you may have to input the values
in the previous table for the machine to work correctly
Please remember a PID is meant to control systems around a steady state. You may set a temperature of 93, but
it’s perfectly normal to see the PID moving from 92 – 93 – 94 and back again. The PID cannot show 0.5 of a C, so
it’s quite likely that this is in reality only 0.5C or less from the set point.
It’s also important to mention that as soon as you use the machine, expect the displayed temperatures to vary a
little after the espresso shot, this is perfectly normal. The boiler is quite large and will very quickly settle down
regardless of any temporary slightly high or low temperature and the group itself is a very temperature stable
(large) mass of metal.
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