Applicatio Manual
Universal Interface 4 DIN/NTC EK- CG2-TP
Revisione 1.0.0 - Aggiornato: 04/09/2017
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Pag. 20
7.3 PWM Proportional-Integral control
The proportional-integral PWM (Pulse Width Modulator) controller uses an analogue control variable to modulate the
duration of the time intervals in which a binary output is in the On or Off state. The controller operates in a periodic manner
over a cycle, and in each period it maintains the output to the On value for a time proportional to the value of the control
variable. As shown in the figure, by varying the ratio between the ON time and the OFF time, the average time of activation
of the output varies, and consequently the average intake of heating or cooling power supplied to the environment
This type of controller is well suited for use with On / Off type actuators, such as relays and actuators for zone
valves, which are less expensive (both for electrical and mechanical components) than proportional actuators. A
distinctive advantage of this type of controller, compared with the raw On / Off controller already described, is that
it eliminates the inertia characteristics of the system: it allows significant energy savings, because you avoid
unnecessary interventions on the system introduced by the 2-point control with hysteresis and it only provides the
power required to compensate for losses in the building.
Every time the user or the supervisor changes the desired temperature setpoint, the cycle time is interrupted, the
control output is reprocessed and the PWM restarts with a new cycle: this allows the system to reach its steady
state more quickly.
Terminal type
Proportional Band [K]
Integral Time [min]
Cycle Period [min]
Radiators
5
150
15-20
Electrical heaters
4
100
15-20
Fan-coil
4
90
15-20
Floor radiant panels
5
240
15-20
i
Guidelines for choosing the proper parameters of a PMW Proportional-Integral controller:
Cycle time: for low-inertial systems such as heating and air conditioning systems, short cycle times must be chosen (10-15
minutes) to avoid oscillations of the room temperature.
Narrow proportional band: wide and continuous oscillations of the room temperature, short setpoint settling time.
Wide proportional band: small or no oscillations of the room temperature, long setpoint settling time.
Short integral time: short setpoint settling time, continuous oscillations of the room temperature.
Long integral time: long setpoint settling time, no oscillations of the room temperature.
OFF
ON
Cycle period
T ON
T OFF
Time [min]
OFF
ON
T ON = T OFF
Time [min]
Mean ON time = 50%
OFF
ON
T ON = ½ T OFF
Time [min]
Mean ON time = 25%
