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Cycle time:
In most cases, the pulse width modulated actuating variables are used to control electro-thermal drives. The room
temperature controller transmits the switching actuating variable telegrams to a switching actuator (preferably with
semi-conductor switching elements) which is connected to the drives.
Setting the cycle time for the PWM signal allows to adapt the control to the drives that are being used. The cycle
time determines the switching frequency of the pulse modulated signal and allows the adaptation to the adjusting
cycle times of the servo drive (traversing time the drive requires to adjust the valve from a completely closed
position to a completely opened position). In addition to the adjusting cycle time the dead time (time during which
the servo drives show no response when switching on or off) has to be considered. If different drives with different
adjusting cycle times are used, the longer time is to be considered. The manufacturer's specifications for the drive
have to be observed.
Two cases for the adjustment of the cycle time can be considered:
I.
Cycle time 2 x adjusting cycle time of the drives being used, for example 15 minutes (default)
In this case, the pulse/pause times of the PWM signal are long enough for the drives to completely open or
close within a time period.
Advantages:
The desired average value for the actuating variable and thus the required room temperature is relatively
accurately adjusted even with several drives that are simultaneously activated.
Disadvantages:
It has to be considered that - due to the constantly 'travelled' full valve lift - the product life of the drives may
decrease. The heat transfer to the room in the vicinity of the heater may be non-uniform and may be felt
bothering to some people if the cycle times are very long ( > 15 minutes) and if the system has a slower
response (for example in case of smaller hot water heaters).
Notes:
• This setting for the cycle time is recommended for slower, more inert heating systems (for example
underfloor heating).
• This setting is also recommended for a larger number of possibly different drives making it easier to average
the valve travel.
II. Cycle time > adjusting cycle time of the drives being used, for example 2 minutes (default)
In this case, the short pulse/pause times of the PWM signal are not sufficient for the drives to completely open
or close within a time period.
Advantages:
This setting ensures a constant water flow through the heaters with a uniform heat transfer to the room.
If only one servo drive is controlled, the controller is able to compensate for the shift of the average value
caused by the short cycle time by continuously adapting the actuating variable and is thus able to adjust the
desired room temperature.
Disadvantages:
If more than one drive is controlled at the same time, the desired average for the actuating variable and thus
the required room temperature is adjusted only very poorly or with larger deviations.
Important:
• This setting for the cycle time is recommended for fast-responding heating systems (for example hot water
heaters with higher flow temperature).
07/17
Subject to change without notice
instabus KNX/EIB System
Sensor
2100-xx/2101 xx Page 39/82
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