Dust monitoring of exhaust gases from manufacturing processes - Manufacturing, Other
DDP, or optical scintillation as it sometimes refe...
DDP, or optical scintillation as it sometimes referred to, measures the dynamic fluctuation in light transmission as dust particles move through a light beam. This dynamic fluctuation derives from temporal distributions of the dust particles which attenuate the light beam. The more dust present in the exhaust, the greater the amplitude of these fluctuations.
DDP instruments calculate the dynamic response, or the ratio of light variation to light intensity, which for particular applications, is proportional to dust concentration and when calibrated against standard reference measurements, this can be presented as a reading in mg/m³.
Unlike the standard transmission technique, DDP has immunity to gradual reductions in the absolute intensity of the light signal. Therefore, DDP instruments have the advantage that they are significantly less susceptible to drift with time, temperature or dirtying optics, than traditional opacity monitors and less sensitive to misalignment. In practice, this means that the instruments require less maintenance.
In order to determine whether DDP is suited to your application, it is necessary to consider a number of factors such as the typical size distribution of the particulates to be measured, whether they have constant or variable physical properties and the ease of which the heads can be accessed for routine cleaning of the optical surfaces. The following table summarises the key requirements for using DDP as compared to the more traditional opacity monitors.
| Parameter |
DDP |
Opacity |
|
Optimum particle diameter (mean of the particle diameter mass distribution) |
>10μm |
<1μm |
|
Dependence on optical properties of the particles |
Low |
High |
|
Dependence on optical surface contamination |
Low |
High |
|
Dependence on noise pick-up (optical or electrical) |
High |
Low |
|
Dependence on gas flow velocity |
High (<3m/s) |
Low |
