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Evaluation of Optical Instruments for Real-Time Continuous Monitoring of Smoke Particulates
2000 Laboratory Tests (continued)—High-humidity tests (relative humidity higher than 70 percent) were performed with DataRam No. 1 configured with no inlet heater and DataRam No. 2 with its inlet heater installed. Figures 24 and 25 show the results from those tests. As previously mentioned, at low relative humidities and with the inlet heater installed, DataRam No. 1 had a slope of 0.70 (R² = 0.76). At high relative humidities without the inlet heater, the slope increased to 1.38 (R² = 0.73). DataRam No. 2 had the inlet heater installed for both the low and high relative humidities tests.
The slope went from 0.80 (R² = 0.79) at low relative humidities to 1.48 (R² = 0.71) at high relative humidities.
Figure 24—Comparison of DataRam No. 1 at low (less than 40
percent) and high (more than 70 percent) relative humidities
during the 2000 laboratory tests. The inlet heater was installed
for the low-humidity tests. The inlet heater was removed
for the high-humidity tests. Gravimetric results are from the
Federal Reference Method sampler.
Figure 25—Comparison of DataRam No. 2 at low (less than 40
percent) and high (more than 70 percent) relative humidities
during the 2000 laboratory tests. The inlet heater was installed
for both the high- and low-humidity tests. Gravimetric results
are from the Federal Reference Method sampler.
Discussion—During the 1998 tests when the instruments were exposed to higher particulate concentrations, the DataRam overestimated concentrations by about 93 percent. During the 2000 laboratory tests the DataRam underestimated lower mass concentrations by 20 to 30 percent. Field tests sampling low concentrations (similar to the 2000 laboratory tests) showed that the DataRam overestimated mass concentrations, but not as much as during the high-concentration 1998 laboratory tests. The differences in the laboratory results may be attributed to the different amount of needles being burned. This caused different flaming and smoldering conditions within the fire and may have generated particulates with different optical properties.
The two DataRams compared similarly during previous tests but accuracy was poor. DataRam No. 2 read about 14 percent higher than DataRam No. 1 throughout the tests. The high-humidity tests indicate that the inlet heater is not entirely effective in reducing the moisture content of the particulate. The instruments continue to overestimate mass concentrations. DataRam No. 1's mass concentration estimates increased by 97 percent when relative humidities were above 70 percent and the inlet heater was not installed. DataRam No. 2's mass-concentration estimates increased by 85 percent when relative humidities were above 70 percent, even when the inlet heater was installed.
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