As particles travel through the process they develop a charge, which is transferred as the particle passes or impacts the sensing element. The resulting current is amplified, filtered, rectified and further filtered looking only at the AC component. This gives a linear representation of the concentration in the gas stream. The reason for measuring the AC component is that compared to the DC component, the electronics are more sensitive. The AC signal is substantially less affected by influences such as amplifier noise and process parameters, which includes the build-up of process dust on the sensing element.
As in the case with VOC emission monitoring particulate measurements can be used to :
- Assess compliance with emission limits set by the appropriate regulatory body (EPA) in the company’s process permit
- Check effects of modifications to the process on the emission levels
- Evaluate the performance of abatement equipment
An example of a particulate monitor : www.durag.com/d_r_800.asp