
ABB i-bus® KNX
PLANNING AND APPLICATION
12.2.13
Control types
The following control types are commonly used for activating valves in heating, ventilation and air condi-
tioning technology.
• Continuous control
• Pulse width modulation (PWM)
• 2-point control
12.2.13.1
Overview of control and control-value types
2-point 1 bit (On/Off)
The 2-point controller switches only when the set operating points are reached. The switch-on and
switch-off commands are sent as 1-bit values on the bus (ABB i-bus® KNX). The 2-point controller
switches as follows:
• Switch-on at setpoint – hysteresis
• Switch-off at se hysteresis
2-point 1 byte (0/100 %)
Unlike 2-point 1 bit (On/Off), the switch-on and switch-off commands are sent as 1-byte values
(0 %/100 %) on the bus (ABB i-bus® KNX).
PI continuous (0 … 100 %)
The PI controller (continuous) adapts its output value to the difference between the actual value and the
setpoint. This adaptation permits exact correction of the room temperature to the setpoint. The control
value is sent as a 1-byte value (0 … 100 %) on the bus (ABB i-bus® KNX). To reduce the bus load, the con-
trol value is sent only if it has changed by a previously specified value.
PI PWM (On/Off)
The PI controller (PWM) converts the calculated control value to a pulse-to-pause ratio. The control value
is sent as a 1-bit value on the bus (ABB i-bus® KNX).
12.2.13.2
2-point controller
A two-point controller has two output states (On/Off) that change based on the actual value:
• If the actual value is higher than the parameterized setpoint, the associated control value is 0.
• If the actual value is lower than the parameterized setpoint, the associated control value is 1.
As the 2-point controller switches only between the On and Off states, the following applications are
possible:
• Activation of a thermoelectric valve connected to a Switch Actuator or a valve drive actuator
• Activation of an electric heater via a relay output
CAUTION
Each change of the control value causes the relay to switch.
▶ Observe the maximum number of operating cycles (service life).
Example
If the control value changes 10 times per day, this corresponds to 3,650 operating cycles per year.
If the control value changes 50 times per day, this corresponds to 18,250 operating cycles per year.
Product manual | EN-US | VC/S 4.x.1 | 2CDC508220D0211 Rev. B
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