LME Series Technical Instructions
Document No. LME-1000
SCC Inc. Page 3 Section 6
Blower Speed Monitoring
To help ensure that the burner is either operated at a safe fuel-to-air ratio or is shut down, the blower
speed is constantly monitored while a flame is present. The speed is monitored in a way that nuisance
shutdowns are eliminated, but fast shutdowns will occur if the speed deviation is large. Two tolerance
bands centered about the target speed are used. These bands are:
1. Tolerance Band 1 - If the speed is within this band, it is considered acceptable and no action is
taken. If the blower speed falls outside of this band, the speed control in the LME7 or the PWM
blower will begin working to get it back inside this band. If the speed does not fall back inside
Tolerance Band 1 within five seconds, a lockout occurs. The width of this band is adjustable via
parameter 650.00 and the range is +/- 1.0 to 5.0% of the maximum blower speed (parameter 519).
2. Tolerance Band 2 - If the blower speed ever falls outside of this band, a lockout occurs immediately.
The width of this band is adjustable via parameter 650.01 and the range is +/- 1.0 to 10.0% of the
maximum blower speed (parameter 519). Tolerance band 2 should be set to a larger value than
tolerance band 1.
These bands are shown graphically in Figure 6-1.
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