Update Process Values - Siemens RXB Series Basic Documentation

Example
outside air temperature
COV = Change of value
Minimum repetition time
Heartbeat
Fault status message
Important notes
For internal use only
Siemens
Building Technologies
9.6

Update process values

Process values such as the outside air temperature can be transmitted to other bus
devices via distribution zones. As the process values rarely are constant,
transmitting every minimal change in value would result in heavy traffic on the bus.
The Synco controller updates the process values (in our example the outside air
temperature) when it changes by a fixed, predefined differential ("delta value").
Thus, the fluctuations in the outside air temperature are added up until the delta
value is reached, and only then is the new value transmitted or updated. The term
COV ("change of value") is applied to process values updated in this way.
If a process value fluctuates widely and the delta value is reached before the
"minimum repetition time" of 10 seconds has expired, there is a delay of 10
seconds before the process value is updated.
With a constant outside air temperature, it may take a long time until the delta
value is reached. For this reason, the outside air temperature is updated every 15
minutes. This is referred to as a "heartbeat".
If the outside air temperature is still not transmitted after the first 15-minute delay,
the controller waits another 15 minutes plus 1 minute (i.e. a total of 31 minutes
since the last update) to transmit a fault status message.
Depending on the application, the controller now continues to operate with the
preset values, e.g. if the outside air temperature sensor is faulty, the flow
temperature is controlled as if the outside air temperature were 0 °C. Certain
functions are also disabled, e.g. there is no summer/winter compensation.
Process values are not updated if the bus device is set to device address 255.
Process values are not updated when the controller is in commissioning mode,
i.e. if the "Commissioning" operating page is selected directly or as part of a
sequence.
KNX bus communications
Appendix
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CE1P3127en
2013-04-08