Performance of Home Smoke Alarms - National Institute of ...

New Signal= 2 − Old Signal(2)With this transformation, new signal decreases with increasing smoke and equation (1) is used tocompute Y. The 2 V cutoff voltage was chosen as an approximate upper limit for the output ofthe alarm.Photoelectric smoke alarm Photo-1: This alarm was modified by adding a sample and hold ICand an amplifier to monitor and amplify the photo-detector signal. It needed a dual powersupply of ± 9 V, which was provided by a series/parallel (6x2) arrangement of 1.5 volt AA sizealkaline batteries. The nominal clean air voltage level was 0.2 V.Photoelectric smoke alarm Photo-3: Identical to Ion-4, this alarm provided a digital signalthat was transmitted to a multiplexing box that converted the digital signal to an analog voltage.The multiplexing box also provided the power to the detector. The clean air voltage level wasnominally 0 V. The voltage output increased in the presence of smoke.Photoelectric smoke alarm ASP-1: This alarm is a commercial design and already has theprovision for an amplified analog voltage proportional to the photodetector signal. It has anintegrated fan that aspirates room air through a special filter medium and into the sensingchamber periodically at a fixed time interval. While it has no smoke entry lag characteristics, itsresponse was affected by the aspiration time interval (normally 30 s). It was powered at 12.0 Vby a variable voltage DC power supply.Carbon monoxide alarm CO-1: This alarm contained a semiconductor tin oxide CO sensorand provided a digital signal that was transmitted to a multiplexing box that converted the digitalsignal to an analog voltage. The multiplexing box also provided the power to the detector. As aconsequence of its programming, this alarm did not produce any voltage change until the COvolume fraction was greater than 50 × 10 -6 (as indicated on the unit’s LED display). Calibrationsfor this alarm start at 50 (volume fraction x10 6 ).Carbon monoxide alarm CO-2: This alarm contained a CO electrochemical cell, and providedan analog voltage proportional to the concentration of CO. These alarms were powered by afresh alkaline 9 volt battery. The nominal clean air voltage level was 0.45 V.Carbon monoxide alarm CO-3: This alarm contained a CO electrochemical cell, and providedan analog voltage proportional to the concentration of CO. 9.00 V was provided by a variablevoltage DC power supply. Clean air voltage level was on the order of 0 V.Representative calibration plots are show in figures 11 to 17 for each alarm type. A singlesmoldering test was used to specify a specific alarm's calibration used for particular test series.20