AS NZS 3580.12.1:2015 pdf download.Methods for sampling and analysis of ambient air Method 12.1: Determination of light scattering- Integrating nephelometer method.
The integrating nephelometer is a continuous direct-reading instrument that measures the light-scattering coefficient of a sample of air and shall meet or exceed the specifications given in Table I. The sample is drawn through a light-proof housing where it is illuminated by a diffuse visible light source and the intensity of the scattered light is measured. The response is sensitive to the spectral characteristics of the instrument. Suitable instruments have a spectral response centred at 500 ±50 nm. As light scattering is a function of the scattering angle the internal optical geometry of the instrument is arranged so that the response of the detector is proportional to the light scattering integrated over all scattering angles. In practice, physical limitations dictate that the integration angle is from approximately 100 to approximately 1 700. The principal features of a nephelometer are shown in Figure 1.
The integrating nephelorneter shall include a sample inlet, sample conditioner, relative humidity sensor and temperature sensor. The nephelometer shall be capable of ensuring that the relative humidity of air sampled is not greater than 60% measured at a point representative of the air in the scattering chamber. The temperature of the air sample measured at a point representative of the air in the scattering chamber shall be maintained at not more than 25°C above ambient temperature.
NOTE: The readings obtained using a nephelometer depends on its internal optical geometry, the spectral characteristics of the light source and the spectral response of the light sensor. hence the readings obtained using different nephelometers are not comparable unless they are of equivalent optical geometry and spectral characteristics.
Consideration shall be given to protecting equipment against excessively high or low temperatures. High temperatures may permanently damage sensitive electronic equipment, while low temperatures may cause condensation to form in sample lines, which can be drawn into instruments, resulting in permanent damage.
With respect to environmental temperature for designated instruments,most units are pre-tested and qualified over a temperature range of 20°C to 30°C and therefore the shelter temperature should lie within these limits. In addition, the temperature should not deviate
from the set point by more than士3°C. Adherence to these limits will contain the amount of drift caused by temperature variations.
In order to detect and correct temperature fluctuations, a 24 h temperature recorder at the instrument site is recommended. These recorders should either be of the continuous recording type or manual max./min. thermometers. Continuous type recorders are useful to determine the stability of the shelter temperature.
Calibration is achieved by spanning the instrument using gases for which the Rayleigh scattering properties are known. FM-200 is a readily available gas providing a suitably high calibration point and should be used as the full scale calibration. Air filtered through a high efficiency filter (Clause 5.5) shall be used to set the zero point. For further information regarding the calibration and response of integrating nephelometers, refer to Appendix A. Calibrations shall be at a frequency not less than those specified in Table 3. NOTE: While chlorofluorohydrocarbons can be used for calibration, consideration should be given to the environmental impact of these gases.
Pressure transducers shall be checked and, if necessary, calibrated at an interval not exceeding twelve months. A reference barometer that complies with the requirements of Clause 5.6 shall be used. The instrument manufacturer’s instructions detailing the specific pressure sensor check and calibration procedure(s) shall be followed.
A check shall also be done whenever an instrument is subject to maintenance or repair that is likely to affect such measurements. If there is a difference of more than ±1 kPa between the transducer and the reference barometer, the transducer shall be calibrated.
Temperature sensors shall be checked and, if necessary, calibrated at an interval not exceeding twelve months. A reference thermometer that complies with the requirements of Clause 5.7 shall be used. The instrument manufacturer’s instructions detailing the specific temperature sensor check and calibration procedure(s) shall be followed.
A check shall also be done whenever an instrument is subject to maintenance or repair that is likely to affect such measurements. If there is a difference of more than ±1°C between the sensor and the reference thermometer, the sensor shall be calibrated.
Relative humidity sensors shall be checked and, if necessary, calibrated at an interval not exceeding twelve months. A reference humidity device that complies with the requirements of Clause 5.8 shall be used. The instrument manufacturer’s instructions detailing the specific relative humidity sensor check and calibration procedure(s) shall be followed.
A check shall also be done whenever an instrument is subject to maintenance or repair that is likely to affect such measurements. If there is a difference of more than ±7% RH between the sensor and the reference humidity device, the sensor shall be calibrated.AS NZS 3580.12.1 pdf download.