Gewiss GW 16 972CB Programmierhandbuch Seite 41

PWM PROPORTIONAL-INTEGRAL
The PWM control algorithm, used to control the temperature adjustment system, allows
you to drastically reduce the times subject to thermal inertia and introduced by the two-
point control. This type of control involves the modulation of the impulse duty-cycle,
represented by the temperature adjustment system activation time, on the basis of the
difference between the fixed set-point and the temperature effectively detected. Two
components are needed to calculate the output function: the proportional component
and the integral component, used to improve the response in order to reach the
temperature at the fixed set-point. Once the proportional band has been defined (from
set-point to set-point -
cooling mode), its width determines the extent of the system's response: if it is too
narrow, the system will be more reactive but with swings; if it is too wide, the system
will be slower. The ideal situation is one where the band is as narrow as possible, without
swings. The integration time is the parameter that determines the action of the integral
component. The longer the integration time, the slower the modification of the output
and hence the slower the system response. If the time is too short, the threshold value
will be exceeded, and the function will swing around the set-point.
Heating
set-point
set-point
cycle time
The device keeps the temperature adjustment system switched on for a cycle time
percentage that depends on the output function of the proportional-integral control; the
device continually adjusts the system, modulating the system ON-OFF times with a duty-
cycle that depends on the value of the output function (calculated at each time gap equal
to the cycle time). The cycle time is reinitialised every time the reference set-point is
modified. With this type of algorithm, there is no longer a hysteresis cycle on the
heating/cooling element, so the inertia times introduced by the two-point control are
eliminated. This produces energy savings because the system does not remain switched
on when it is not needed and, once the required temperature has been reached, it
continues to provide a limited contribution to compensate for the environmental heat
dispersion.
USER INSTRUCTIONS
for heating mode, from set-point to set-point +
Air-cooling
set-point
set-point
41
for
cycle time
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