Aethalometer Module, Series 8100 - Thermo EGS Gauging - #1

The filter tape rests on a support through which the pumping suction is applied. Light penetrating the particle deposit and filter tape passes to a photodiode located directly underneath the tape. The ongoing collection of BC-containing particles causes the filter spot to darken, and the intensity of light detected by the photodiode (the "sensing" voltage) gradually dimin­ishes.

A second photodiode is installed under a "clean" portion of the filter tape to provide a reference mea­surement and correct for any slight changes in lamp output intensity. The rate of change of the corrected "sensing" voltage is interpreted as the rate at which BC is collecting on the filter, proportional to the instanta­neous BC mass concentration in the sampled air stream.

The firmware periodically measures the photodiode signals with the lamp turned off to determine and account for any zero offsets.

An electronic circuit board converts the optical signals from the sensing and reference sensors into digital data, and passes the values to a microprocessor for calculating the BC concentration.

The Aethalometer Module firmware computes a five-minute rolling average of the BC concentration that is updated every minute. The unit sends the average BC concentration to the TEOM monitor's control unit through a cable as an analog voltage. The TEOM monitor converts the input into a numeric value in engineering units that can be displayed and stored.

When the filter spot density reaches a preset limit, the tape advances automatically to provide a fresh collec­tion area. While advancing the filter tape and making initial measurements in the new sampling position, the Aethalometer Module maintains the most current valid BC concentration as its output. The unit updates the

The Series 8100 Aethalometer Module provides a simple, cost effective means for users of TEOM Ambient Particulate Monitors to perform black carbon (BC) aerosol measurements. The module provides a continuous output of the black carbon content of ambient particulate matter (PM), while the TEOM monitor simultaneously measures the total PM mass concentration. The unit is the result of a collaborative effort between R&P and Magee Scientific, the devel­oper of the Aethalometer technology.

Aethalometer monitors from Magee Scientific have been used worldwide as a stand-alone instrument to determine the impact on human health and the environ­ment due to particles released from the combustion of fossil fuels and agricultural burning. The method is the foremost approach for the real-time measurement of optically-absorbing black carbon aerosols.

The Series 8100 Aethalometer Module can be easily integrated into any existing or new TEOM Series 1400 Ambient Particulate Monitor operating at 1 m³/h (16.7 l/min) through attachment to the TEOM bypass flow. The output signal from the BC module is trans­mitted through a cable to the control unit of the TEOM monitor, where BC mass concentration values are displayed and stored.

The bypass flow from the TEOM monitor enters and exits the Aethalometer Module on the unit's rear panel. The sample stream is split internally into a 2 l/min analytical flow that passes through the BC sensor, and an excess flow that recombines before exiting the module.

The 2 l/min analytical flow passes through an area of filter tape in the BC sensor head, where particles collect on a "deposit spot" illuminated by a high inten­sity infrared (880 nm) LED lamp.

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Features Sheet, Series 8100 Aethalometer Module, Nov 05, Page 1