Impact Of The Reference Gas; Switching On And Switching Off; Aging - Siemens QGO21 Series Basic Documentation

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Assessment of aging with
the help of the LMV52 with
PLL52 and AZL52
18/27
Building Technologies Division

5.3 Impact of the reference gas

When the oxygen concentration of the reference gas changes, the point of intersection
of the straight line with the abscissa will change (20.9%).
Figure 5: Nernst voltage as a function of the reference gas
Note
The QGO21 is a device that does not measure the absolute but the relative oxygen
value.
The result is calculated based solely on the ratio of the partial pressures of the
reference gas (ambient air) and the measuring gas.

5.4 Switching on and switching off

When switching the sensor on or off, temperature differences generate thermo-electric
voltages of up to 100 mV (both positive and negative).
These can produce erroneous measurements during the heating up phase.
It is recommended to observe the heating up times specified in Engineering notes.

5.5 Aging

Due to aging, the characteristics internal resistance and electrical response time can
change.
The LMV52 with PLL52 measures these characteristics at regular intervals and triggers
an alarm should programmable limits be exceeded.
On the display, the following value can be checked:
- Internal resistance:
If these limit is exceeded, the QGO21 must be replaced.
Oxygen Sensor QGO21...
5 Description of functions
Max. 150 
CC1P7845en
06.12.2017