ABB Busch-priOn Series Technical Reference Manual page 13

Internal temperature sensor
The device has an integrated temperature sensor. The measured value enters the control as actual value. The value can
also be shown on the display.
In addition, the measured temperature can be transferred to the bus via the 2-byte communication object "Send actual value
- temperature sensor", to be shown on the display, for example. Sending takes place in dependence of parameters "Send
actual value for change greater than" and "Send actual value cyclically". By default, both parameters are deactivated. This
means that at least one setting must be activated if the actual temperature is to be sent.
The setting "Send actual value for change greater than" has the advantage of being able to transmit the smallest change in
the measured temperature, adjustable from 0.1 k to 1.0 K, to the bus. The disadvantage is, for example, that at a setting of
0.1 K and a lot of room thermostats within an installation, the load on the bus increases.
The parameter "Send actual value cyclically" has the advantage that the current actual value is sent out continuously, even
when the measured value does not change. The disadvantage is that rapid changes may not be registered because the
cycle time selected is too large. It should also not be small because of the extreme load the bus is subjected to.
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External temperature sensor
In open-plan offices it can be difficult to control the temperature with only a single thermostat. That is why it would be
advantageous to divide the room into zones with an additional room thermostat.
To integrate the temperature value of the additional temperature sensor into the temperature control, the parameter "Room
temperature measurement" must be set on "Internal and external". The the temperature measured inside and outside can
then be additionally weighted. The setting for weighting depend on the local circumstances. If the room thermostat and the
additional measuring sensor are positioned equal distances from the heater, in the case of panel heaters, a 50% / 50%
setting should provide good control results.
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Monitoring
The "Temperature measurement monitoring" parameter specifies whether the external temperature sensor and the outside
temperature are to be monitored. This means that the room thermostat has to receive at least one telegram with the current
temperature on the associated communication object within an adjustable time ("Monitoring time of external temperature"
and "Monitoring time of outside temperature").
If no telegram is received during monitoring time, the room thermostat assumes that the measuring sensor for the outside
temperature or external temperature is defective or no longer connected to the bus.
The room thermostat will then terminate its control and send a predefined control value ("Control value during temperature
measurement error") so that the room to be controlled does not overheat or cool down. This control value is sent out until the
room thermostat again receives a temperature telegram via the bus and reactivates the control.
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Adjustment
If the measured temperature is distorted, such as by the inherent heat of the bus coupler, an "Offset room temperature
measurement" can be set.
If additional external temperature recording has been activated and the measured value becomes distorted through the
influence of cold or heat, here, too, an offset can be entered.
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KNX Technical Reference Manual | 0073-1-7388 | 13