Integrating Nephelometer 3563
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The Integrating Nephelometer 3563 is a unique analytical instrument useful for short-or long-term measurements of the light-scattering coefficient of atmospheric and laboratory aerosols. It is particularly well-suited for measurements related to climate, visibility, and air quality.
This unique instrument offers sensitivity to light scattering coefficients lower than 1.0 x 107 meter-1 (blue and green wavelengths, 30-sec average time). That's as much as two orders of magnitude better than other commercial instruments!
TSI's Integrating Nephelometerl 3563 has the advantage of selectable averaging time, allowing data to be tailored to different test requirements. It includes temperature and humidity sensors, and it possesses high vacuum integrity. Therefore, it produces accurate measurements, even when positioned inside pressurized aircraft cabins or smoke-filled environments.
This three-color nephelometer allows you to measure both total and backscatter signals, and it operates under complete computer control. Software and a separate power supply (not pictured) are also included with the instrument.
To find out more about how TSI's Integrating Nephelometer 3563 works, its operating principles, and the technology behind it, check out this link on the NOAA website.
Features and Benefits
- Sensitivity to light scattering coefficients lower than 1.0 x 10-7 meter-1
- Selectable averaging time
- Climate, visibility, and air-quality measurements
- Integrating Nephelometer software
- Power supply
Are nephelometer measurements independent of temperature and pressure? Does the instrument measure correctly at lower pressures?
The scattering values that TSI's nephelometer provides are the scattering values of the particles, no matter what the temperature or pressure might be. The scattering of particles is neither temperature nor pressure dependent! However, the total scattering measured by the instrument also includes contributions from air molecules (Rayleigh scattering) and the wall. Rayleigh scattering is temperature and pressure dependent, but it is well known. The instrument corrects for it automatically. The wall scatter is measured during a zero measurement. The corrected Rayleigh scatter, along with the measured wall scatter, are subtracted from the measured total to give the resulting particle scatter. Thus, TSI's nephelometer will measure correctly even at lower pressures (for example, on top of a mountain).
Forcing seems to be one of the key words in the whole global climate change discussion. What does it actually mean?
Forcing means anthropogenic, that is, man-made, or externally imposed change to the planetary energy balance. So, the effects that aerosols generated by industry, combustion, and so forth have on the Earth's climate are part of the climate forcing. A good example of forcing is to picture the Kuwaiti oil fires during the Gulf War. The burning of the oil fields lasted for many days, generating a huge cloud of smoke. This situation had the potential for serious effects on the environment.
How should I take a sample for my nephelometer?
A simple one-inch diameter tube extending out from the nephelometer inlet, or whatever distance is necessary to avoid contamination, is fine. If the tube is conductive, it minimizes the possibility of charged-induced losses. Sedimentation losses only occur for large particles (that is, larger than 5 µm), but these do not contribute significantly to particle scattering, especially since the forward scattering is not detected. The sample flow is provided by the nephelometer blower. Of course, the exhaust for the nephelometer should be filtered as for all other instruments.
What about sample heating inside a closed cavity nephelometer?
The TSI nephelometer heats the sample by about 2 to 4 degrees, depending on the flow and the lamp voltage. This lowers the relative humidity and decreases particle scattering. The effect is greatest at high humidity (RH >80%) and becomes negligible at low humidity (RH <50%). Turning down the lamp voltage reduces the effect, but also reduces the signal. It is better to use large flows and ventilate the instrument as much as possible to keep it cool. You can also run it with the cover off. In any case, TSI's nephelometer allows you to monitor the heating caused by the instrument, as both inlet and sample temperature are recorded.
What is the BNC Input Voltage?
The BNC Input Voltage is intended as an analog input that can be used to monitor an event outside the nephelometer. You can, for example, monitor the sample temperature or relative humidity upstream of the instrument with an external sensor (needs to have 0 to 5 V analog output). You can then log this data with the rest of the nephelometer data for post analysis. In the past, the record of this input showed an oscillation when left unused. We now have reconfigured it to have a stable zero value when not in use.
What is the difference between nephelometers with open and closed cavity design?
There are two schools of thought. One school says visibility is what they want to measure, at existing humidity, and the best way to do that is to use an open-cavity nephelometer, even though it eliminates water droplets that are bigger than a couple of 10 µm. Open-cavity nephelometers, therefore, allow fog and mist to affect the measurement. The other school says, because you cannot measure accurately at existing humidity, and because you are interested in apportioning fractions of the aerosol to a man-made source, you should try to control humidity. Closed-cavity design units, such as the TSI nephelometer, sample aerosol into a sensing zone, permitting the user to condition the sample so fog and mist do not affect the measurement. The preferred instrument depends on the purpose of the measurement. If aerosol pollution is of interest, fog and mist are interferences. The closed-chamber design allows the control of relative humidity (by heating), thus providing a separate measurement of the scattering coefficient and the increase in it due to relative humidity. This must occur because the necessary companion measurements (concentration, etc.) also must be measured at a point in space and at a known, low relative humidity. TSI nephelometers do this.