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Date: 8-4-2010
Revision: 0
Form: 2396
Stager can execute an AddStage or DropStage
request.
Add Stage Methods
Various methods can be used to determine
when a new stage should be added. The internal
algorithms that generate AddStageRequests
are called Add-stage methods.
All methods work by observing various criteria
such as the Firing stages, the commanded rate,
or setpoint error.
Adding Stages Parameters:
ADD-STAGE DETECTION TIME1: MM:SS
This provides time thresholds.
In the descriptions below, the relevant
parameter is referred to as Add-Stage
detection timeN.
Add-Stage method1:
Disable,
Error threshold,
Rate threshold,
dError/dt and threshold,
dRate/dt and threshold }
In the descriptions below, the relevant
AddStageDetect- Timer is referred to as
AddStageDetectTimerN.
ADD-STAGE ERROR THRESHOLD:
DEGREES
This provides the error threshold as defined by
the methods below.
ADD-STAGE RATE OFFSET: -100% TO +100%
This provides the rate offset threshold as
defined by the methods below.
Add-stage methods
ERROR THRESHOLD
For error threshold staging, a stage is added
when the error becomes excessive based on
degrees away from setpoint, and time.
ADD-STAGE CONDITION:
- The modulating burner(s) is at its (their)
maximum position per the rate allocation rules,
- The operating point is below the setpoint by an
amount greater than or equal to Add-stage
error threshold
When the Add-stage condition is false then
AddStage- DetectTimerN is set to zero. (If the
condition is true then AddStageDetectTimerN
is not zeroed and thus allowed to run.) If this
timer reaches or exceeds LLAdd- stage
detection timeN then AddStageRequestN is
true.
RATE THRESHOLD For rate based staging, a
stage is added based on the rate of the
modulating stage.
ADD-STAGE CONDITION:
The modulating burner is at a rate that is at or
above the rate which is calculated by adding the
Add-stage rate offset to the maximum position
per the rate allocation rules.
Examples: rate offset = 20% The add-stage
condition will occur if the modulating stage is
20% above base load for unlimited allocations,
or, if limited, when there is 20% more rate to
distribute than can be absorbed by firing the
stages at base load.
rate offset = -20% The add-stage condition will
be as described just above, but the threshold is
now 20% below the modulating stage's base
load rate.
To support this, the current Rate Allocation
method asks for the current "Overflow rate" -
see the Rate Allocator section.
Drop Stage Methods
Various methods can be used to determine
when a stage should be dropped. The internal
algorithms that generate DropStageRequests
are called Drop-stage methods.
One or two methods may be active at any time.
If two are active then their requests are OR'd
together.
All methods work by observing various criteria
such as the Firing stages, the commanded rate,
or Setpoint.
Dropping Stages Parameters:
DROP-STAGE DETECTION TIME: MM:SS
This provides time thresholds. They differ only in
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