How The O 2 Is Measured With The Qgo20 Sensor And Pll52 Module - Siemens LMV5 Series Technical Instructions

Technical Instructions
Document No. LV5‐1000
If only the O alarm function is to be used and the O
2
parameters must be set. These are:
1. O2 MaxValue ‐ set to the maximum safe %O
2. O2 Alarm curve ‐ enter the minimum safe %O
3. Tau Low‐FireOEM ‐ the delay time of the burner / boiler at low fire
4. Tau High‐FireOEM ‐ the delay time of the burner / boiler at high fire
5. OptgMode ‐ set to O2 Limiter
If the O trim has not been commissioned, it will be necessary to manually enter Tau Low‐FireOEM and
2
Tau High‐FireOEM. These Tau times do not have to be as accurate as if the O
These can be manually timed by using the O
be used. Higher turndown burners will produce longer low fire Tau times. Typically, for a 5‐to‐1
turndown burner, Tau Low‐FireOEM is between 10‐20 seconds. Tau High‐FireOEM is typically 4
seconds or less.
How the O is Measured with the QGO20 Sensor and PLL52 Module
2
The QGO20 is a Zirconium type sensor that is heated to approximately 1292°F. The high temperatures
allow oxygen to diffuse through the Zirconium cell and produce a milli‐volt signal. This milli‐volt signal is
referred to as the Nernst Voltage. The Nernst Voltage that is produced for a given %O
the concentration of oxygen and the temperature of the Zirconium cell. The PLL52 module reads both
the Nernst Voltage and the temperature of the Zirconium cell. With this information, the %O
accurately determined and sent back to the LMV52 over CANbus.
As well as taking the milli‐volt signals and converting these to CANbus data, the PLL52 also serves as the
controller for the Zirconium cell's heating element. The PLL52 is also a place to connect the combustion
air temperature sensor and the stack gas temperature sensor.
Three milli‐volt signals originate in the QGO20:
1. Nernst Voltage from the Zirconium oxide O
2. O cell thermocouple signal
2
3. Cold junction thermocouple compensation
These three milli‐volt signals between the QGO20 and the PLL52 must be run in a separate conduit and /
or a shielded cable.
See Section 2 for complete details on wiring the QGO20 to the PLL52.
High voltage wires are also connected from the PLL52 to the QGO20 for the heater. It is very important
that these wires are run in a separate conduit away from the milli‐volt signals.
NOTE: Never connect the QGO20 heater directly to line voltage! Permanent damage will result to the
heating element and the sensor. High voltage wires for the heater to the QGO20 must come from the
PLL52 module. See Section 2 for more information.
Also, due to possible interference on the milli‐volt signals, the PLL52 must be installed within 30 feet of
the QGO20.
Section 6 Page 26 SCC Inc.
trim has not been commissioned, a few key
2
(wet) for all points.
2
(wet) for each point.
2
reading on the AZL (recommended), or typical values can
2
cell terminals B1 and M
2
terminals B2 and M
terminals G2 and U3
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trim was being used.
2
is dependent on
2
can be
2