| 摘要 |
A hollow cell with opposed windows is connected in series with conduits through which automobile exhaust gas to be analyzed flows continuously. A broadband infrared source directs a beam through the windows to a first photodetector which measures the absorption of light at one wavelength to which one of the gas components, such as carbon monoxide (CO), is responsive. This beam is alternately directed over a longer path through the cell by a reflective chopper wheel adjacent the exit window and by mirrors mounted outside both windows to another photodetector which measures absorption of light at a different wavelength corresponding to another component, such as a hydrocarbon (HC). The outputs of both photodetectors are utilized to give continuous direct readout of the concentrations of the components. Each window is formed with a length of transparent plastic tape releasably sealed against the cell body and connected to a roll of the tape mounted adjacent to the cell. A clean window is provided by simply advancing a fresh length of tape into the cell and discarding the used portion.
|
