Siemens QGO21 Series Basic Documentation page 9

Functional check
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Building Technologies Division
After the final mounting check, a first functional check can be made:
Before commissioning for the first time or after replacing the QGO21, the QGO21 must
be checked for temporary O2 measured value distortion.
The QGO21 must measure the O2 value with sufficient accuracy before an O2 setpoint
curve is set.
Humidity deposits in the QGO21 can lead to O2 measured value distortion. In the first
few hours after the QGO21 is switched on, the O2 measured values may be distorted,
resulting in the values being too low.
Example: 4.1% O2 content may be shown instead of 5%.
The following measures must be implemented to prevent distorted O2 measurements:
1. Operate the QGO21 continuously on the system under voltage for at least 8 hours
with the sensor heating switched on.
2. Then operate the burner in pre-ventilation phase for 15 minutes and observe the
O2 measured value until a value between 19.5% and 21% is measured. If this has
still not happened after 15 minutes in pre-ventilation phase, there is a temporary
O2 measured value distortion. The O2 setpoint curve must not be set.
New QGO21 devices must be pre-heated for up to 12 hours longer before no
temporary O2 measured value distortion occurs and a relevant O2 value is
achieved in the pre-ventilation phase.
Older QGO21 devices must be replaced or cleaned if the relevant O2 value is not
achieved in the pre-ventilation phase within the specified time frame.
Note!
Important point to remember for urea injection and other sources of humidity:
Humidity reduces the O2 value in the flue gas.
Example: If an O2 setpoint curve is set when a humidity source is active, the O2
control can reduce the air more than desired during normal operation if the humidity
source stops working at a later stage. Sufficient oxygen reserves must be taken into
account in the O2 setpoint curve for this eventuality.
It is also possible to make a functional check of the QGO21 based on a comparative
measurement.
Comparative measurement means that, during burner operation, the actual oxygen
value is measured with a flue gas analyzer and will then be compared with the value
acquired by the QGO21.
Note
Flue gas analyzers measure «dry», the QGO21 measures wet.
The conversion is made with the help of the conversion table contained in the
Addendum to this Basic Documentation.
Oxygen Sensor QGO21...
1 Safety notes
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CC1P7845en
06.12.2017