Siemens LMV5 Quick Start Manual page 177
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Two additional requirements of the O2 trim are that there is at least a 0.5% O2 gap between the
O2 Monitor curve and the O2 Control curve, and that there is at least a 1.0% O2 gap between
the O2 Control Curve and the O2 Ratio Control curve.
The LMV52 will not allow the O2 curve points to be entered if they do not meet these minimum
gap requirements. These requirements should be kept in mind when commissioning the Fuel-Air
Ratio Curve since the Fuel-Air Ratio Curve will usually have to be set at least 1.0 % O2 leaner
than on a non-O2 trim system.
As was briefly mentioned earlier, the O2 trim is only able to move the actuators that are
designated as air influen(ced) back on their individual curves. Figure 6-1.2 illustrates this
action by detailing a small piece of the same Fuel-Air Ratio curves that were shown back in
Figure 4-1.11. For this example the air actuator is the only actuator designated as
air influen(ced) and the Fuel and Aux1 actuators are at Point 5.
In Figure 6-1.2 the O2 trim is responding to a measured O2 value that is higher than the O2
Control curve at Point 5. Thus, the LMV52 is moving the air actuator back down its curve to
lower the %O2 that is being sensed in the stack.
Figure 6-1.2 Actuator movement in response to high measured O2 values
It should also be noted that the LMV52 cannot open any air influen(ced) actuator farther than
the point the fuel actuator is at.
For Example : If the LMV52 was held at Point 5 (or 43 percent load in this example, see 6-1.1)
the air actuator could never open up beyond its Fuel-Air Ratio Curve position at Point 5 of 29
degrees, even if the %O2 measured in the stack was below the O2 Control curve at Point 5. If
the %O2 in the stack went lower than the O2 Monitor curve, then the O2 trim would deactivate
and / or cause a lockout, depending on how parameter OptgMode is set.
If this parameter is set to conAutoDeact, the LMV52 will only deactivate the O2 trim, and will
continue to function. If the O2 trim automatically deactivates, the actuators will operate on the
Fuel-Air Ratio curves that were defined during the Fuel-Air Ratio Control commissioning.
LMV5 QSG Rev 4
Sec 6 Pg 3
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