O 2 Sensor Reading Grossly High Or Low; O 2 Sensor Reads But Responds Very Slowly - Siemens LMV5 Series Technical Instructions

Technical Instructions
Document No. LV5‐1000
If the O readings from the O
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1. The milli‐volt signals from the QGO20 to the PLL52 could have interference. Ensure that the
high and low voltage wires that run from the QGO20 to the PLL52 are in a separate conduit.
2. The QGO20 sensor reads %O
number shown on the AZL52 is typically at least 1% O
3. The QGO20 sensor may be mounted incorrectly, and the sensor is not picking up a
representative reading of the %O
If the %O being displayed is responding slowly to combustion changes, check the following:
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1. Ensure that the QGO20 sensor is clean. This can be done by shutting off the power to the
LMV52, and removing the QGO20 from the stack. Be careful as the sensor is likely to be very
hot. After the QGO20 is removed from the stack, let it cool for at least an hour.
After the sensor has cooled, it can be blown out using low pressure compressed air (less
than 15 PSIG) through the top of the sensor and out the front. If this is done when the
QGO20 sensor is hot, the ceramics inside the sensor will most likely be cracked and the
sensor will need to be replaced.
2. Check the orientation of the QGO20 sensor and the AGO20 collector. The one notch on the
AGO20 collector's flange should be between the two notches on the QGO20 sensor's flange.
Also, ensure that the bevel of the collector is pointed into the flow of the stack gas.
3. Check the internal resistance of the QGO20 sensor using the following menu path:
Params & Display > O2 Module > Process Data > QGO Resistance
This value increases as the sensor ages. As the internal resistance increases, the response
time of the sensor also increases. A new sensor has 0 Ohms, while the maximum resistance
is 150 Ohms, indicating replacement of the sensor is necessary.
Section 7
O2 Sensor Reading Grossly High or Low
sensor are grossly high or low, check the following:
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wet. Most combustion analyzers read %O
2
in the stack.
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O2 Sensor Reads But Responds Very Slowly
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dry, so the O
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lower than the combustion analyzer.
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LMV Series
2
SCC Inc.