FB-AP Drift Compensation
All FB-AP Series smoke detectors include compensation for sensor drift as part of the internal signal-processing algorithm. The algorithm will compensate for changes in sensor output caused, for example, by dust in the chamber, and will therefore hold the sensitivity at a constant level even with severe chamber contamination. This increased stability is achieved without significantly affecting the detector’s sensitivity to fire.
The compensation level is stored in the detector’s memory as a single value between 0 and 31. The normal level, that is, with no compensation applied, is 16. Values above or below this indicate drift towards alarm or away from alarm respectively.
For compensation values in the range 4 to 30 the detector is working within its allowable range. A value which is less than 4 or greater than 30 results in a warning flag. A value of zero results in a fault signal.
The maximum compensation that can be applied is 31. If further drift occurs, the analog values will simply track the drift and the detector will become more sensitive.
Compensation values are stored in nonvolatile memory and will be retained even if detectors are disconnected. It is possible to use the control panel to ascertain the level of compensation applied at any time.
For the FB-AP Series smoke detectors, the compensation algorithms are designed such that the detectors meet the fire code requirements in all response modes.
It is possible, through the protocol, to carry out a normalization procedure which rapidly “updates” the drift compensation. This facility may be useful during commissioning allowing detectors to quickly acclimate to the prevailing ambient conditions, or after a compensated detector has been cleaned.